,illustration3 ,,frontispiece4--,half-stereogram of ,mount ,ellsworth1 drawn to illustrate the form of the displacement and the progress of the erosion4 ,the base of the figure represents the sea-level4 ,the remote half shows the result of uplift alone2 the near half1 the result of uplift and erosion1 or the actual condition4 7,see page #ie47 ,,department ,,of ,,the ,,interior4 ,u4 ,s4 ,,geographical ,,and ,,geological ,,survey ,,of ,,the ,,rocky ,,mountain ,,region4 ,j4 ,w4 ,,powell1 ,,in ,,charge4 ,,report ,,on ,,the ,,geology ,,of ,,the ,,henry ,,mountains4 ,by ,g4 ,k4 ,,gilbert4 ,illustration3 ,logo ,,washington3 ,,government ,,printing ,,office4 #ahgg4 ,,department ,,of ,,the ,,interior1 ,u4 ,s4 ,,geographical ,,and ,,geological ,,survey ,,of ,,the ,,rocky ,,mountain ,,region1 ,washington1 ,d4 ,c41 ,march #e1 #ahgg4 ,,sir3 ,i have the honor to transmit herewith a report on the ,geology of the ,henry ,mountains1 by ,mr4 ,g4 ,k4 ,gilbert4 ,i am1 with great respect1 your obedient servant1 ,j4 ,w4 ,,powell1 ,in charge4 ,the ,hon4 ,,secretary ,,of ,,the ,,interior1 ,washington1 ,d4 ,c4 ,,department ,,of ,,the ,,interior1 ,u4 ,s4 ,,geographical ,,and ,,geological ,,survey ,,of ,,the ,,rocky ,,mountain ,,region1 ,washington1 ,d4 ,c41 ,march #a1 #ahgg4 ,,dear ,,sir3 ,i submit herewith my report on the ,geology of the ,henry ,mountains1 prepared from material gathered under your direction in the years #ahge and #ahgf4 ,i am1 with great respect1 your obedient servant1 ,g4 ,k4 ,,gilbert4 ,prof4 ,j4 ,w4 ,,powell1 ,in charge4 ,,preface4 ,if these pages fail to give a correct account of the structure of the ,henry ,mountains the fault is mine and ,i have no excuse4 ,in all the earlier exploration of the ,rocky ,mountain ,region1 as well as in much of the more recent survey1 the geologist has merely accompanied the geographer and has had no voice in the determination of either the route or the rate of travel4 ,when the structure of a mountain was in doubt he was rarely able to visit the points which should resolve the doubt1 but was compelled to turn regretfully away4 ,not so in the survey of the ,henry ,mountains4 ,geological exploration had shown that they were well disposed for examination1 and that they promised to give the key to a type of structure which was at best obscurely known2 and ,i was sent by ,professor ,powell to make a study of them1 without restriction as to my order or method4 ,i was limited only in time1 the snow stopping my work two months after it was begun4 ,two months would be far too short a period in which to survey a thousand square miles in ,pennsylvania or ,illinois1 but among the ,colorado ,plateaus it proved sufficient4 ,a few comprehensive views from mountain tops gave the general distribution of the formations1 and the remainder of the time was spent in the examination of the localities which best displayed the peculiar features of the structure4 ,so thorough was the display and so satisfactory the examination1 that in preparing my report ,i have felt less than ever before the desire to revisit the field and prove my conclusions by more extended observation4 ,in the description of the details of the structure a demand arose for a greater number of geographic titles than were readily suggested by natural forms or other accidents1 and recourse was had to the names of geologists4 ,except that the present members of my own corps are not included1 the names chosen are of those whose cognate studies have given me most aid4 ,mr4 ,steward and ,mr4 ,howell saw the ,henry ,mountains before ,i did1 and gleaned something of their structure from a distance2 ,dr4 ,newberry1 ,mr4 ,marvine1 ,dr4 ,peale1 and ,mr4 ,holmes have described allied phenomena in ,colorado and ,new ,mexico2 and the works of ,messrs4 ,jukes1 ,geikie1 ,scrope1 and ,dana have been among my chief sources of information in regard to igneous mountains in general4 ,if any of these gentlemen feel offended that their names have been attached to natural features so insignificant1 ,i can assure them that the affront will never be repeated by the future denizens of the region4 ,the herders who build their hut at the base of the ,newberry ,arch are sure to call it 8the ,cedar ,knoll02 the ,jukes ,butte will be dubbed 8,pilot ,knob01 and the ,scrope1 8,rocky ,point04 ,during the preparation of my report every part of the discussion has been submitted to ,professor ,powell for criticism1 and many of his suggestions are embodied in the text4 ,similar and valuable aid was received from ,capt4 ,c4 ,e4 ,dutton and ,mr4 ,william ,b4 ,taylor in the study of the physical problems to which the discussion of the intrusive phenomena gave rise4 ,captain ,dutton rendered an important service also by the study of the collection of igneous rocks1 and his report1 included in the fourth chapter1 testifies to the thoroughness of his work4 ,the supervision of the publication has fallen in large share upon ,mr4 ,j4 ,c4 ,pilling1 and the text has had the advantage of his literary criticism1 as well as of his watchful care4 ,g4 ,k4 ,g4 ,,contents4 ,page4 ,,chapter ,i4 ,,introductory #a ,the rock series #c ,unconformities #h ,the ,great ,folds #aa ,cliffs and plateaus #ac ,how to reach the ,henry ,mountains #ad ,,chapter ,,ii4 ,,structure ,,of ,,the ,,henry ,,mountains #ah ,,chapter ,,iii4 ,,detailed ,,description ,,of ,,the ,,mountains #bb ,mount ,ellsworth #bb ,mount ,holmes #bg ,mount ,hillers #cj ,mount ,pennell #ce ,mount ,ellen #ch ,stereogram of the ,henry ,mountains #di ,,chapter ,,iv4 ,,the ,,laccolite #ea ,the ,henry ,mountains intrusives1 by ,captain ,c4 ,e4 ,dutton #fa ,the question of cause #gb ,the stretching of strata #hj ,the conditions of rock flexure #hc ,the question of cover and the question of age #hd ,the history of the laccolite #ie ,laccolites of other regions #ig ,possible analogues of the laccolite #ih ,,chapter ,v4 ,,land ,,sculpture #ii ,i4 ,erosion #ii ,a4 ,processes of erosion #ii ,weathering #ajj ,transportation #aja ,corrasion #aja ,b4 ,conditions controlling erosion #ajb ,rate of erosion and declivity #ajb ,rate of erosion and rock texture #ajc ,rate of erosion and climate #ajc ,transportation and comminution #ajf ,transportation and declivity #ajh ,transportation and quantity of water #aji ,corrasion and transportation #aaa ,corrasion and declivity #aab ,declivity and quantity of water #aac ,,ii4 ,sculpture #aae ,sculpture and declivity #aae ,the law of structure #aae ,the law of divides #aaf ,sculpture and climate #aag ,bad-lands #abj ,equal action and interdependence #abc ,,iii4 ,systems of drainage #abd ,the stability of drainage lines #abd ,the instability of drainage lines #abe ,the stability of divides #ach ,the instability of divides #aci ,consequent and inconsequent drainage #adc ,the drainage of the ,henry ,mountains #add ,,chapter ,,vi4 ,,economic #aea ,,chapter ,i4 ,,introductory4 ,the ,henry ,mountains have been visited only by the explorer4 ,previous to #ahfi they were not placed upon any map1 nor was mention made of them in any of the published accounts of exploration or survey in the ,rocky ,mountain region4 ,in that year ,professor ,powell while descending the ,colorado ,river in boats passed near their foot1 and gave to them the name which they bear in honor of ,prof4 ,joseph ,henry1 the distinguished physicist4 ,in #ahgb ,prof ,a4 ,h4 ,thompson1 engaged in the continuance of the survey of the river1 led a party across the mountains by the ,penellen ,pass1 and climbed some of the highest peaks4 ,frontiersmen in search of farming and grazing lands or of the precious metals have since that time paid several visits to the mountains2 but no survey was made of them until the years #ahge and #ahgf1 when ,mr4 ,walter ,h4 ,graves and the writer visited them for that purpose4 ,they are situated in ,southern ,utah1 and are crossed by the meridian of #aaj #de and the thirty-eighth parallel4 ,they stand upon the right bank of the ,colorado ,river of the ,west1 and between its tributaries1 the ,dirty ,devil and the ,escalante4 ,at the time of their discovery by ,professor ,powell the mountains were in the center of the largest unexplored district in the territory of the ,united ,states--a district which by its peculiar ruggedness had turned aside all previous travelers4 ,up to that time the greater part of the knowledge that had been gained of the interior of the continent had been acquired in the search for routes for transcontinental railways2 and the caons of the ,colorado ,basin1 opposing more serious obstacles to travel than the mountain ranges which were met in other latitudes1 were by common consent avoided by the engineers4 ,the same general causes which have rendered the region so difficult of access and passage have made it a desert1 almost without economic value4 ,the physical conditions of elevation and aridity which have caused it to be so deeply carved in caons1 have prevented the streams with which it is scantily watered from being bordered by tracts of land which can be irrigated2 and agriculture without irrigation being in that climate an impossibility1 there is nothing to attract the farmer4 ,as will be explained in the sequel1 the mountains offer no inducements to the miner of the precious metals4 ,there is timber upon their flanks and there is coal near at hand1 but both are too far removed from other economic interests to find the market which would give them value4 ,it is only for purposes of grazing that they can be said to have a money value1 and so distant are they at present from any market that even that value is small4 ,but while the ,henry ,mountains contribute almost nothing to our direct material interests1 they offer in common with the plateaus which surround them a field of surpassing interest to the student of structural geology4 ,the deep carving of the land which renders it so inhospitable to the traveler and the settler1 is to the geologist a dissection which lays bare the very anatomy of the rocks1 and the dry climate which makes the region a naked desert1 soilless and almost plantless1 perfects the preparation for his examination4 ,the study of the mountains is further facilitated by their isolation4 ,they mark a limited system of disturbances1 which interrupt a region of geological calm1 and structurally1 as well as topographically1 stand by themselves4 ,the ,henry ,mountains are not a range1 and have no trend2 they are simply a group of five individual mountains1 separated by low passes and arranged without discernible system4 ,the highest rise about #e1jjj feet above the plateau at their base and #aa1jjj feet above the level of the ocean4 ,projecting so far above the surface of the desert1 they act as local condensers of moisture1 and receive a comparatively generous supply of rain4 ,springs abound upon their flanks1 and their upper slopes are clothed with a luxuriant herbage and with groves of timber4 ,the smaller mountains and the foot-hills of the larger are less generously watered and but scantily clothed with vegetation4 ,their extent is small4 ,from ,ellen ,peak to ,mount ,ellsworth1 the two summits which are the most widely separated1 the distance is but twenty-eight miles1 and a circle of eighteen miles radius will include the whole group4 ,mount ,ellen which is the most northerly of the group1 has an extreme altitude of #aa1bej feet1 and surpasses all its companions in horizontal extent as well as altitude4 ,its crest-line is continuous for two miles1 with an elevation varying little from #aa1jjj feet4 ,from it there radiate spurs in all directions1 descending to a series of foot-hills as conspicuous in their topography as they are interesting in their structure4 ,in some places the base of the mountain is guarded by a continuous1 steep ridge1 through which a passage must be sought by the approaching traveler1 but within which movement in any direction is comparatively unimpeded4 ,mount ,pennell is a single peak rising to an altitude of #aa1aej feet4 ,on one side its slopes join those of ,mount ,ellen in ,pennellen ,pass 7#g1eej feet71 and on the other those of ,mount ,hillers in the ,dinah ,creek ,pass 7#g1cjj feet74 ,its profiles are simple1 and it lacks the salient spurs that characterize ,mount ,ellen4 ,from the west it is difficult of approach1 being guarded by a barrier ridge continuous with that of ,mount ,ellen4 ,mount ,hillers is more rugged in its character1 and although compact in its general form1 is carved in deep gorges and massive spurs4 ,its rugosity is contrasted by the smoothness of its pedestal1 which to the south and west and north is a sloping plain merging with the surrounding plateau4 ,mount ,ellsworth 7#h1jjj feet7 and ,mount ,holmes 7#g1gej feet7 stand close together1 but at a little distance from the others4 ,the pass which separates them from ,mount ,hillers has an altitude of #e1bej feet4 ,they are single peaks1 peculiarly rugged in their forms1 and unwatered by springs4 ,they stand almost upon the brink of the ,colorado1 which here flows through a caon #a1ejj feet in depth4 ,,the ,,rock ,,series4 ,the sedimentary rocks which occur in the ,henry ,mountains and their immediate vicinity1 range from the summit of the ,cretaceous to the summit of the ,carboniferous4 ,it is probable that they were covered at one time by some thousands of feet of ,tertiary strata1 but from the immediate banks of the ,colorado these have been entirely eroded1 and their nearest vestiges lie thirty miles to the westward1 where they have been protected by the lava-beds of the ,aquarius ,plateau4 ,cretaceous4--,the ,cretaceous strata do not reach to the ,colorado ,river1 but they extend to the ,henry ,mountains1 and are well displayed upon the flanks4 ,they include four principal sandstones1 with intervening shales1 in the following 7descending7 order3 #a4 ,the ,ma-suk ,sandstone1 yellow1 heavy-bedded #ejj feet4 #b4 ,the ,ma-suk ,shale1 gray1 argillaceous1 and toward the top slightly arenaceous #ejj feet4 #c4 ,the ,blue ,gate ,sandstone1 yellow and heavy-bedded #ejj feet4 #d4 ,the ,blue ,gate ,shale1 blue-black and argillaceous1 weathering to a fine gray clay 7,inoceramus deformis and ,i4 problematicus7 #a1jjj feet4 #e4 ,the ,tu-nunk ,sandstone1 yellow and heavy-bedded #ajj feet4 #f4 ,the ,tu-nunk ,shale1 blue-black and argillaceous1 weathering to a fine gray clay 7,inoceramus problematicus and ,baculites anceps7 #djj feet4 #g4 ,the ,henry's ,fork ,group1 consisting of-- a4 ,friable yellow sandstone with numerous fossils 7,ostrea prudentia1 ,gryphea ,pitcheri1 ,exogyra lviuscula1 ,exogyra ponderosa1 ,plicatula hydrotheca1 ,camptonectes platessa1 and ,callista ,deweyi7 #aj feet4 b4 ,arenaceous shales1 purple1 green1 and white1 with local beds of conglomerate #aij feet4 c4 ,coarse sandstone and conglomerate1 with many white grains and pebbles1 interleaved with local beds of purple and red shale1 and containing immense silicified tree-trunks #cjj feet4 ---------- ,total ,cretaceous #c1ejj feet4 ,the three upper sandstones1 the ,masuk1 the ,blue ,gate1 and the ,tununk1 are so nearly identical in their lithologic characters that ,i was unable to discriminate them in localities where their sequence was unknown4 ,this was especially the case upon the summits of ,mounts ,ellen and ,pennell where they occur in a somewhat metamorphosed condition4 ,all of them contain thin beds of coal1 none of which are continuous over large areas1 and only one of which was observed of workable thickness4 ,at the western foot of ,mount ,ellen1 a bed four feet thick lies at the base of the ,blue ,gate ,sandstone4 ,there is almost equal difficulty in discriminating the ,masuk1 the ,blue ,gate1 and the ,tununk shales4 ,the first is usually of a paler color and is more apt to include arenaceous bands4 ,it has not been found to contain fossils1 while the lower shales rarely fail to afford them when search is made4 ,the ,blue ,gate and ,tununk shales are typical examples of fine argillaceous sediments4 ,they are beautifully laminated and are remarkably homogeneous4 ,it is only in fresh escarpments that the lamination is seen1 the weathered surface presenting a structureless clay4 ,the fossils of these shales are so numerous1 when they have been sought out and studied1 that they will probably serve not merely to discriminate the two1 but also to correlate them with some of the beds which have been examined elsewhere in the ,colorado ,basin4 ,for the present ,i am unable to refer any of the ,cretaceous rocks above the ,henry's ,fork ,group to the divisions which have been recognized elsewhere1 and it is for this reason that ,i have given local1 and perhaps temporary names to such beds as ,i have need to mention in the discussion of the structure of the mountains4 ,the fossils of the ,henry's ,fork ,group have been more fully collected1 and they have been referred without question by ,dr4 ,white to the group of that name1 as recognized in the ,green ,river ,basin 7,geology of the ,uinta ,mountains1 pp4 #hb and #id74 ,the white grit which lies at the base of the group is a conspicuous bed of unusual persistence1 and is recognized wherever ,cretaceous rocks are found in the upper basin of the ,colorado4 ,jura-,trias4--,the rocks which intervene between the base of the ,cretaceous and the summit of the ,carboniferous are of doubtful age1 having been referred to the ,trias by one geologist and to the ,jura and ,trias by others1 while the fossils recently discovered by ,mr4 ,howell 7,geology of ,uinta ,mountains1 page #hj7 lead to the suspicion at least that they are all ,jurassic4 ,it is probable that the uncertainty will soon be dispelled by the more thorough working of ,mr4 ,howell's new localities2 but while it remains1 it seems best to recognize its existence in our nomenclature1 and ,i shall include the whole of the doubtful series under the title of ,jura-,trias4 ,at the ,henry ,mountains it is easily divided into four groups1 as follows3 #a4 ,flaming ,gorge ,group2 arenaceous shales or bad-land sandstones1 purple and white at top and red below #a1bjj feet4 #b4 ,gray ,cliff ,group2 massive cross-laminated sandstone1 buff to red in color #ejj feet4 #c4 ,vermilion ,cliff ,group2 massive cross-laminated sandstone1 red1 with a purple band at the top #ejj feet4 #d4 ,shin-ar-ump ,group2 consisting of-- a4 ,variegated clay shale2 purple and white above and chocolate below1 with silicified wood #cjj feet4 b4 ,gray conglomerate1 with silicified wood2 the 8,shinarump ,conglomerate0 #cj feet4 c4 ,chocolate-colored shale1 in part sandy #djj feet4 ---------- ,total ,jura-,trias #b1icj feet4 ,the rock of the ,flaming ,gorge ,group is of a peculiar character4 ,it is ordinarily so soft that in its manner of weathering it appears to be a shale4 ,it is eroded so much more rapidly than the ,henry's ,fork conglomerate above it1 that the latter is undermined1 and always appears in the topography as the cap of a cliff4 ,nevertheless1 it is not strictly speaking a shale4 ,the chief product of its weathering is sand1 and wherever it can be examined in an unweathered condition it is found to be a fine-grained sandstone1 massive and cross-laminated like those of the ,gray and ,vermilion ,cliffs1 but devoid of a firm cement4 ,in a number of localities it has acquired1 locally and accidentally1 a cement1 and it is there hardly distinguishable from the firmer sandstones which underlie it4 ,in the immediate vicinity of the ,henry ,mountains it varies little except in color from summit to base1 but in other localities not far distant it is interrupted near the base by thick beds of gypsum and gypsiferous clays1 and by a sectile1 fossiliferous limestone4 ,the ,gray ,cliff and ,vermilion ,cliff sandstones are often difficult to distinguish1 but the latter is usually the firmer1 standing in bold relief in the topography1 with level top1 and at its edge a precipitous face4 ,the former is apt to weather into a wilderness of dome-like pinnacles1 so steepsided that they cannot often be scaled by the experienced mountaineer1 and separated by narrow clefts which are equally impassable4 ,the colors of the two sandstones are not invariable4 ,the lower1 which although not reddened throughout its mass is usually stained upon its surface with a uniform deep color1 appears in ,mount ,ellsworth and at other points of elevation with as pale a tint as that of the ,gray ,cliff4 ,the latter sandstone1 on the other hand1 where it lies low1 is often as deep in color as the ,vermilion4 ,standing upon one of the summits of the ,henry ,mountains and looking eastward1 ,i found myself unable to distinguish the ,gray ,cliff ,sandstone by color either from the lower part of the ,flaming ,gorge ,group or from the ,vermilion ,sandstone4 ,the bleaching of the redder sandstone in ,mount ,ellsworth is probably a result of metamorphism2 the reddening of the gray sandstone may depend on the hydration of the iron which it contains4 ,the thickness of individual strata in these great sandstones is remarkable1 and is one of the elements which must be taken into account in the discussion of the problem--which to my mind is yet unsolved--of the manner in which such immense quantities of homogeneous sand were accumulated4 ,ordinarily the depth of strata is indefinable1 on account of the impossibility of distinguishing stratification from lamination2 but where1 as in this case1 the lamination is oblique to the stratification1 the upper and lower limits of each stratum are definitely marked4 ,i have at several points measured single strata with thicknesses of about fifty feet1 and near ,waterpocket ,caon a stratum of ,vermilion ,cliff sandstone was found to be #aje feet thick4 ,one other measurement is worthy of record2 the inclination which oblique lamination bears to the plane of the stratum in which it occurs appears to have a definite limit4 ,the maximum of a series of measurements made at points where to the eye the dip seemed to be unusually great1 is #bd4 ,the sandy layers at the base of the ,shinarump ,group are characterized by profuse ripple-marks4 ,carboniferous4--,beneath the ,jura-,trias is the ,carboniferous4 ,a few hundred feet of its upper member1 the ,aubrey ,sandstone1 are exposed near the summit of ,mount ,ellsworth4 ,at that point the sandstone is altered to the condition of a quartzite1 but where it is cut by the upper and lower caons of the ,dirty ,devil ,river it is massive and cross-laminated1 differing from the ,gray ,cliff sandstone chiefly in the abundance of its calcareous cement4 ,,unconformities4 ,from the ,masuk ,sandstone to the ,aubrey ,sandstone1 inclusive1 there is perfect conformity of dip4 ,the fold system of the region1 of which a description will be found in succeeding pages1 was established after the deposition of all these strata1 and the whole series were flexed together4 ,nevertheless1 the strata do not represent continuous deposition4 ,there were intervals in which the sea receded and exposed to erosion the sediments which it had accumulated4 ,shallow valleys and waterways were excavated1 and when the sea returned it deposited new sediments upon the somewhat uneven surface of the old4 ,the first occurrence of this sort was at the close of the ,aubrey epoch4 ,its evidence was not found in the ,henry ,mountains2 but at the confluence of the ,paria with the ,colorado1 eighty miles to the southeast1 the surface of the upper member of the ,aubrey ,group1 which is there a cherty limestone1 is unevenly worn1 and in its depressions are beds of conglomerate1 the pebbles of which are derived from the chert of the limestone itself4 ,the shaly1 rippled sandstones which succeed this conglomerate indicate that the water remained shallow for a time1 and in the middle of the ,shinarump epoch the region was once more abandoned by the sea4 ,the chocolate shales and shaly sands were unevenly worn1 and the first deposit that the returning sea spread over them was a conglomerate4 ,the evidence of this break is found at many points4 ,the ,shinarump conglomerate although remarkably persistent for a conglomerate thins out and disappears at a number of points1 and at the margins of its areas it is evident to the eye that it occupies depressions of the surface on which it rests4 ,the next break is at the base of the ,vermilion ,cliff ,group4 ,in the region of the ,virgin ,river and ,kanab ,creek the change from the variegated shales of the ,upper ,shinarump to the homogeneous sandstone of the ,vermilion ,cliff is gradual1 the interval being filled by a series of alternating shales and sandstones2 but further to the east1 in the region of the ,henry ,mountains and ,waterpocket ,caon1 the change is abrupt1 and the firm sandstone rests directly upon the soft shale4 ,the abruptness of the change would suggest that the currents which brought the sand had swept away all evidence of the intermediate conditions which are likely to have connected the epochs represented by the two sediments2 but in one locality1 at least1 there is direct evidence that the surface of the clay was exposed to the air before it was covered by the sand4 ,on the northern flank of ,mount ,ellsworth are the vestiges of a system of mud-cracks1 such as form where wet clays are dried in the sun4 ,where the under surface of the ,vermilion sandstone is exposed to view1 it is seen to be marked by a network of ridges which once occupied the sun-cracks of the ,shinarump clay2 and where the clay is seen in juxtaposition1 tapering fillets of sand can be traced from the ridges downward ten feet into the clay4 ,illustration3 ,,fig4 #a4--;,fossil ,suncracks in the ,shinarump ,shale4 ,from the base of the ,vermilion to the summit of the ,cretaceous no evidence of land erosion has been found2 but the association of coal seams with all of the ,cretaceous sandstones except the lowest1 shows that the sea-bottom was frequently brought to the surface of the water if it was not carried above4 ,thus it is evident that the strata of the ,henry ,mountain region do not represent continuous sedimentation4 ,at the close of the ,aubrey epoch1 in the middle of the ,shinarump1 and again at the close of the ,shinarump1 not merely was the accumulation of sediments interrupted1 but the process was reversed1 and a portion of the deposits which had already been formed were excavated by the agency of rains and rivers1 and swept away to some other region4 ,each break is indefinite1 alike as regards the interval during which the record of the sea was interrupted and as regards the extent of the record which was at the same time obliterated4 ,and yet the evidence of these breaks is of such nature that it would probably elude observation if a single section only were examined1 and in a region masked by the soil and vegetation of a humid climate it would hardly be discovered except by accident4 ,the parallelism of contiguous strata is not alone sufficient evidence that they were consecutive in time4 ,at the close of the ,cretaceous period there came an epoch of disturbance4 ,the system of strata which has been described was bent into great waves1 and the crests of the waves were lifted so high above the sea that they lost thousands of feet by erosion4 ,in the troughs between the waves lakes remained1 in which the material removed from the crests was redeposited1 and by a later change the lake waters rose so as to cover the truncated crests1 and deposit upon the worn edges of the upbent strata a series of unconforming1 fresh-water1 ,tertiary sediments4 ,thus was produced the only unconformity of dip which involves the ,henry ,mountain rocks1 and even this is not to be observed in the immediate vicinity of the mountains1 for a later erosion has thence removed all of the ,tertiary strata1 and has resumed the degradation of the older beds4 ,,the ,,great ,,folds4 ,the disturbances at the close of the ,cretaceous period were of the ,kaibab type#a4 ,it seems as though the crust of the earth had been divided into great blocks1 each many miles in extent1 which were moved from their original positions in various ways4 ,some were carried up and others down1 and the majority were left higher at one margin than at the other4 ,but although they moved independently1 they were not cleft asunder4 ,the strata remained continuous1 and were flexed instead of faulted at the margins of the blocks4 ,subsequent erosion has obliterated in great part the inequality of the surface1 and the higher-lying blocks do not stand as mountains1 but are outlined by zones of tilted strata which mark the flexures by which the blocks are separated4 ,along the zones of flexure it frequently happens that a hard stratum outcropping between two that are softer will be preserved from erosion and form a long1 continuous ridge4 ,such ridges1 and other forms produced by the erosion of the flexures1 are conspicuous features of the topography1 and the tracing out of the limits of the blocks is a simple matter4 ,indeed the flexures are the first elements of the structure to attract attention1 and it is easy in studying them to overlook the fact that they merely mark the limits between displaced masses of great extent4 ,if the reader will examine ,plate ,i at the end of the volume1 he will observe that the system of parallel ridges and valleys which follow the line of the ,waterpocket flexure are very conspicuous features2 but it is only by some such generalization as that given in the stereogram of the same region 7,plate ,,ii7 that the full structural significance of the flexures can be realized4 ,each map was obtained by photography from a model in relief1 in which the proportionate heights of the several features were not exaggerated4 ,the stereogram was produced by the restoration of the top of the ,cretaceous1 the ,masuk sandstone1 in the form and position it would have1 had there been no erosion of the region1 but displacement only4 ,footnote #a3 ,for a definition of the ,kaibab structure1 see 8,geology of the ,uinta ,mountains10 pp4 #ad and #ag1 and ,american ,journal of ,science for ,july and ,august1 #ahgf1 pp4 #ba and #he4 ,i must caution the reader against an implication of rigidity which might attach to the meaning of the word 8block01 as ,i have used it in speaking of the great displaced rock masses4 ,to what extent they may be regarded as rigid is uncertain1 but the presence upon their surfaces of numerous minor flexures1 such as appear in the stereogram1 would seem to imply that their rigidity is not of a high order4 ,in the northwest corner of the area represented by the stereogram are a few faults belonging to a system which occupies a large area in that direction4 ,the system of faults and the system of flexures are independent1 the latter having originated at the close of the ,cretaceous period1 and the former after the formation of the ,tertiary rocks of the region1 which are referred by ,professor ,powell to the ,bitter ,creek epoch4 ,over a large district the ,tertiary strata were covered by a deep mantle of lava1 which has protected them from erosion to such an extent that the structure of the district is portrayed in its topography4 ,the district is its own stereogram1 each uplifted block constituting a mountain and each depressed block flooring a valley4 ,not all the displacements of the later system are by faulting1 but by far the greater number4 ,of the earlier system of displacements none are simple faults1 but a few are combinations of fault and flexure4 ,illustration3 ,,fig4 #b4--;,cross-section of the ,waterpocket ,flexure1 opposite the ,masuk ,plateau4 ,scale1 one inch #c1ejj feet4 #a1 ,masuk ,sandstone4 #b1 ,masuk ,shale4 #c1 ,blue ,gate ,sandstone4 #d1 ,blue ,gate ,shale4 #e1 ,tununk ,sandstone4 #f1 ,tununk ,shale4 a1 ,gryphea ,sandstone4 #g1 ,henry's ,fork ,conglomerate4 #h1 ,flaming ,gorge ,shale4 #i1 ,fossiliferous ,limestone4 #aj1 ,gray ,cliff ,sandstone4 #aa1 ,vermilion ,cliff ,sandstone4 #ab1 ,upper ,shinarump ,shale4 #ac1 ,shinarump ,conglomerate4 #ad1 ,lower ,shinarump ,shale4 #ae1 ,aubrey ,sandstone4 ,illustration3 ,,fig4 #c4--,view of the ,waterpocket ,caon and the ,waterpocket ,flexure4 ,the cliff at the left is capped by the ,henry's ,fork ,conglomerate4 ,the arched rocks at the right are the ,gray and ,vermilion ,cliff ,sandstones4 ,illustration3 ,,fig4 #d4--,waterpocket ,flexure1 as seen from the south end of ,mount ,ellen4 ,the ,waterpocket flexure1 represented in the stereogram 7,plate ,,ii71 is better known in detail than any other of the great flexures of ,southern ,utah4 ,it is far from following a straight line1 but like most lines of orographic disturbance swerves to the right and left1 while maintaining a general trend4 ,the amount of its 8throw01 or the difference in level between adjacent parts of the two blocks which it divides1 is inconstant1 its maximum being #g1jjj feet4 ,at some points the flexed strata are inclined at an angle of #ej while at others their greatest dip is but #ae4 ,toward the north the flexure twice divides4 ,one of its branches1 the ,blue ,gate flexure1 has a throw in the same direction1 and by its separation diminishes the throw of the main flexure4 ,the other1 the ,red ,gate flexure1 has a throw in the opposite direction1 and by its separation increases the throw of the main flexure4 ,or in other words1 the blocks at the west of the main flexure stand higher than those at the east2 and of two blocks which lie at the west1 that at the north of the ,red ,gate flexure stands higher than that at the south2 while of two blocks at the east1 that which lies northwest of the ,blue ,gate flexure is higher than the one at the southeast4 ,,cliffs ,,and ,,plateaus4 ,let us now return to the topographic map 7,plate ,i7 and examine the forms into which erosion has wrought the disturbed strata4 ,thanks to the aridity of the climate1 the erosion has been greatly influenced by the varying texture of the rocks4 ,every hard stratum1 if inclined1 stands forth in a ridge1 or if level1 caps a plateau4 ,the ,masuk ,sandstone1 undermined by the weathering of the ,masuk ,shale1 breaks off everywhere in a cliff which completely encircles the ,masuk ,plateau4 ,the plateau stands upon the ,blue ,gate ,sandstone1 and this breaking off in a cliff upon all sides constitutes another plateau4 ,the ,blue ,gate ,plateau1 in turn1 rests upon the ,tununk1 and that again upon the ,henry's ,fork4 ,passing either to the north or to the south from the ,masuk ,plateau1 one descends a great geological stairway1 of which each step is a hard sandstone and each riser a soft shale4 ,toward the ,waterpocket flexure the edge of each plateau is upturned1 and if one goes westward from the ,masuk ,plateau1 he will cross in the first mile the upturned rocks of all the lower tables4 ,the preservation of the ,masuk ,plateau is due in part to the fact that it lies in a slight synclinal1 but chiefly to the arrangement of the drainage lines4 ,no streams cross the ,henry ,mountains1 but all go around1 and the plateau occupies the divide between those which flow southward to the ,colorado and those which flow northward to the ,dirty ,devil4 ,the antithesis of the ,masuk ,plateau is to be seen in the ,circle ,cliffs1 on the summit of the ,waterpocket fold4 ,at the lowest point of the ,masuk synclinal a circling cliff has been formed1 which facing outward surrounds a plateau4 ,at the highest point of the ,waterpocket fold1 which is in a certain sense anticlinal1 a circling cliff has been formed which1 facing inward1 surrounds a valley4 ,the two phenomena are alike illustrations of the law that in regions of inclined strata cliffs face toward districts of elevation and away from districts of depression4 ,,how ,,to ,,reach ,,the ,,henry ,,mountains4 ,illustration3 ,,fig4 #e4--,ways and ,means4 ,no one but a geologist will ever profitably seek out the ,henry ,mountains1 and ,i will therefore1 in marking out a route by which they may be reached1 select whenever there is option those paths which will give him the best introduction to this wonderful land4 ,there is no wagon-road to the mountains1 and although a wagon might carry his baggage the greater part of the way1 he must provide himself with other means of transportation4 ,at ,salt ,lake ,city he can procure pack-mules and pack-saddles1 or apparajos1 and everything necessary for a mountain 8outfit04 ,his route southward follows the line of the ,utah ,southern ,railway to ,juab ,valley1 and then touches the ,mormon towns of ,nephi1 ,gunnison1 and ,salina4 ,at ,salina he halts his train for a day while he rides a few miles up the creek to see the unconformity between the ,tertiary above1 and the ,jura-,trias and ,cretaceous below4 ,this is at present the last settlement on the route1 but there are 8ranches0 as far as ,rabbit ,valley1 and if he delays a few years he will find a town there4 ,by way of the 8,twist0 road and ,king's ,meadows he goes to ,grass ,valley1 and thence to ,fish ,lake4 ,the lake lies between two upheaved blocks of trachyte1 and covers one which is relatively depressed1 and tilted to the north4 ,at the south end of the lake he stands on the higher end of the depressed block1 and if he follows the shore to the outlet at the north he will find that the water is contained by a moraine1 which has been thrown across the valley by an ancient glacier1 descending from the mountain at the west4 ,from ,fish ,lake he goes to ,rabbit ,valley1 and there delays a day or two to climb ,thousand ,lake ,mountain4 ,looking west from the summit he sees the lava-capped plateaus of the faulted district among which he has journeyed since he left the 8,twist0--huge tables of trachyte bounded by cliffs of displacement1 of which only the sharpest edges have been worn away2 and when his eye has become accustomed to the facies of the faults1 he perceives that there is an identity in structure between the great and the small features4 ,just as the whole district is divided into blocks1 of which the dimensions are measured by miles1 and the displacements by thousands of feet1 so the greater blocks are sometimes divided into smaller1 of which the dimensions are measured by rods and furlongs and the displacements by tens and hundreds of feet4 ,looking eastward he sees the region of the great flexures spread out before him like a map4 ,the ,waterpocket flexure starts from the very mountain beneath him1 and curving to the right1 runs far to the south and is lost in the distance4 ,beyond it are the ,henry ,mountains springing abruptly from the desert2 and against the horizon are outlined other island mountains1 gray in the distance4 ,to the left is the ,san ,rafael ,fold1 the rival of the ,waterpocket in grandeur2 and all about are tables and cliffs4 ,the vivid hues of the naked rocks are obscured only by the desert haze1 and the whole structure is pictured forth by form and color4 ,illustration3 ,,fig4 #f4--,the ,unconformity of the lower caon of ,salina ,creek4 ,the horizontal strata are ,tertiary2 the inclined1 ,cretaceous4 ,to reach the ,henry ,mountains from ,rabbit ,valley1 he must cross the ,waterpocket flexure2 and so continuous and steep are the monoclinal ridges which follow the line of flexure1 that there are but four points known where he can effect a passage4 ,except at these points1 the barrier is impassable from ,thousand ,lake ,mountain to the ,colorado ,river1 a distance of eighty miles4 ,the most difficult and circuitous route ,i will not describe4 ,the remaining three diverge but slightly from each other4 ,starting from ,rabbit ,valley he follows for a few miles the valley of the ,dirty ,devil1 which here1 through the 8,red ,gate01 passes from the trachyte plateaus and enters the land of caons4 ,he does not follow it far1 but where the river enters a caon in the ,aubrey ,sandstone1 bears to the left1 and by the aid of a trail which ,indians have made finds a sinuous but easy pathway along a monoclinal valley1 following the outcrop of the lower ,shinarump4 ,at his right the ,aubrey ,sandstone rises to form the plateau through which the river defiles4 ,at his left the ,vermilion ,sandstone stands in a vertical wall4 ,beneath his feet are the shaly sandstones of the ,shinarump ,group1 bare of vegetation and displaying a profusion of ripple-marks1 such as is rarely if ever equaled4 ,a ride of twelve miles brings him once more to the ,dirty ,devil ,river1 which emerging from its ,carboniferous caon dives at once into a still deeper caon through the ,vermilion and ,gray ,cliff ,sandstones4 ,he can follow the river if he tries1 and emerge with it beyond the flexure2 but the way is difficult and the ,indian trail he has followed thus far leads on to another caon4 ,the monoclinal valley which has opened so easy a way continues for fifteen miles farther1 and in that distance is crossed by four waterways1 each of which leads by a narrow caon through the great sandstones4 ,the first and fourth are impassable4 ,the second carries no permanent stream1 and is called the 8,capitol ,caon04 ,the third affords passage to ,temple ,creek4 ,the smoothest road lies through ,capitol ,caon1 but the ,temple ,creek ,caon has an advantage in the presence of water1 and is furthermore attractive by reason of the picture-writings on the walls4 ,he has now to cross the ,blue ,gate flexure1 and to do this he leaves ,temple ,creek a little below the mouth of its caon4 ,seeking once more the guidance of a trail1 he journeys southeastward over the gypsum and sand of the ,flaming ,gorge ,group to a pass which from a distance he has detected in the monoclinal ridge marking the ,henry's ,fork conglomerate4 ,through this pass ,tantalus ,creek sometimes runs on its way to join the ,dirty ,devil1 and he may find a stream of muddy water2 but the bottom is more likely to be dry with the exception of a few pools4 ,passing through the gap he finds before him a similar opening in the ,tununk ,ridge1 and beyond that a break in the ,blue ,gate ,cliff4 ,from ,tantalus ,creek he ascends to the pass in the ,blue ,gate ,cliff1 and climbing to the summit of a sharp divide in the shales descends again to ,lewis ,creek1 which there follows a caon through the ,blue ,gate ,plateau4 ,here he finds bowlders of the ,henry ,mountain trachyte--for ,lewis ,creek rises in the ,henry ,mountains--and a few hours' ride toward the sources of the stream brings him to the base of ,mount ,ellen4 ,distances4 ,from ,salt ,lake ,city to ,salina #aee miles4 ,from ,salina to ,fish ,lake #ch miles4 ,from ,fish ,lake to ,rabbit ,valley #bg miles4 ,from ,rabbit ,valley to ,temple ,creek ,caon #bg miles4 ,from ,temple ,creek ,caon to ,lewis ,creek #ah miles4 ,thence to the base of ,mount ,ellen #aj miles4 ------ ,total from ,salt ,lake ,city to the ,henry ,mountains #bge miles4 ,,chapter ,,ii4 ,,the ,,structure ,,of ,,the ,,henry ,,mountains4 ,the mountains stand within the province of the great flexures1 but are independent of them4 ,fifteen miles to the westward runs the ,waterpocket flexure4 ,thirty miles to the north is the ,san ,rafael fold4 ,at the east the strata rise toward a great uplift1 of which the full form is unknown4 ,but where the ,henry ,mountains stand the rocks are unaffected by these disturbances4 ,they have a uniform dip of about #de to the northwest1 and form a perfect datum-plane from which to measure the magnitude of the displacements which have given rise to the mountains4 ,the mountains are composed of a large number of parts which are in a certain degree individual and homologous4 ,by the generalization of the characters of those parts a conception has been obtained of a type structure to which the entire series of phenomena has been referred4 ,in laying the material before the reader1 the following plan will be followed3 ,first4 ,the type of structure will be briefly set forth4 ,second4 ,the phenomena by which the type is at once demonstrated and illustrated will be described in detail4 ,third4 ,the type of structure will be discussed4 ,if the structure of the mountains be as novel to the reader as it was to the writer1 and if it be as strongly opposed to his preconception of the manner in which igneous mountains are constituted1 he may well question the conclusions in regard to it while they are unsustained by proof4 ,i can only beg him to suspend his judgment until the whole case shall have been presented4 ,on some accounts it would have been well to follow in writing the order of investigation1 and develop the general plan of structure as it was developed in the field1 by the addition here of one element and there of another2 or at least to assemble the facts before announcing my deductions4 ,but such a course would be at the expense of an important element of convenience and brevity4 ,as will appear in the sequel1 the preliminary explanation of the type structure furnishes a complement of categories and terms by the aid of which the description of the details of observation1 essentially tedious1 is greatly abbreviated4 ,illustration3 ,,fig4 #g4--;,ideal ,cross-section of a ,mountain of ,eruption4 ,illustration3 ,,fig4 #h4--;,ideal ,cross-section of a ,laccolite1 showing the typical form and the arching of the overlying strata4 ,it is usual for igneous rocks to ascend to the surface of the earth1 and there issue forth and build up mountains or hills by successive eruptions4 ,the molten matter starting from some region of unknown depth passes through all superincumbent rock-beds1 and piles itself up on the uppermost bed4 ,the lava of the ,henry ,mountains behaved differently4 ,instead of rising through all the beds of the earth's crust1 it stopped at a lower horizon1 insinuated itself between two strata1 and opened for itself a chamber by lifting all the superior beds4 ,in this chamber it congealed1 forming a massive body of trap4 ,for this body the name laccolite 71 cistern1 and 1 stone7 will be used4 ,figure #g and ,figure #h are ideal sections of a mountain of eruption and of a laccolite4 ,the laccolite is the chief element of the type of structure exemplified in the ,henry ,mountains4 ,it is evident that the intrusion of a laccolite will produce upon the surface as great a hill as the extrusion of the same quantity of matter1 the mass which is carried above the original surface being precisely equivalent to that which is displaced by the laccolite2 and it is further evident that where the superior rock is horizontally stratified every stratum above the laccolite will be uplifted1 and1 unless it is fractured1 will be upbent1 and will portray1 more or less faithfully1 by its curvature1 the form of the body it covers4 ,associated with the laccolites of the ,henry ,mountains are sheets and dikes4 ,the term sheet will be applied in this report to broad1 thin1 stratified bodies of trap1 which have been intruded along the partings between sedimentary strata1 and conform with the inclosing strata in dip4 ,dikes differ from sheets in that they intersect the sedimentary strata at greater or less angles1 occupying fissures produced by the rupture of the strata4 ,the logical distinction between dike and sheet is complete1 but in nature it not unfrequently happens that the same body of trap is a sheet in one place and a dike in another4 ,between the sheet and the laccolite there is a complete gradation4 ,the laccolite is a greatly thickened sheet1 and the sheet is a broad1 thin1 attenuated laccolite4 ,illustration3 ,,fig4 #i4--;,ideal ,cross-section of a ,laccolite1 with accompanying ,sheets and ,dikes4 ,in the district under consideration the laccolite is usually1 perhaps always1 accompanied by dikes and sheets 7see ,figure #i74 ,there are sheets beneath laccolites and sheets above them4 ,the superior sheets have never been observed to extend beyond the curved portion of the superior strata4 ,dikes rise from the upper surfaces of the laccolites4 ,they are largest and most numerous about the center1 but1 like the superior sheets1 they often extend nearly to the limit of the flexure of the uplifted strata4 ,the larger often radiate from the center outward1 but there is no constancy of arrangement4 ,where they are numerous they reticulate4 ,in the accompanying diagrams dikes are represented beneath as well as above the laccolites4 ,these are purely hypothetical1 since they have not been seen4 ,in a general way1 the molten rock must have come from below1 but the channel by which it rose has in no instance been determined by observation4 ,the horizontal distribution of the laccolites is as irregular as the arrangement of volcanic vents4 ,they lie in clusters1 and each cluster is marked by a mountain4 ,in ,mount ,ellen there are perhaps thirty laccolites4 ,in ,mount ,holmes there are two2 and in ,mount ,ellsworth one4 ,mount ,pennell and ,mount ,hillers each have one large and several smaller ones4 ,illustration3 ,,fig4 #aj4--;,ideal ,cross-section of ,grouped ,laccolites4 ,their vertical distribution likewise is irregular4 ,some have intruded themselves between ,cretaceous strata1 others between ,jura-,triassic1 and others between ,carboniferous4 ,from the highest to the lowest the range is not less than #d1jjj feet4 ,those which are above not unfrequently overlap those which lie below1 as represented in the ideal section1 ,figure #aj4 ,the erosion of the mountains has given the utmost variety of exposure to the laccolites4 ,in one place are seen only arching strata2 in another1 arching strata crossed by a few dikes2 in another1 arching strata filled with a network of dikes and sheets4 ,elsewhere a portion of the laccolite itself is bared1 or one side is removed so as to exhibit a natural section4 ,here the sedimentary cover has all been removed1 and the laccolite stands free1 with its original form2 there the hard trachyte itself has been attacked by the elements and its form is changed4 ,somewhere1 perhaps1 the laccolite has been destroyed and only a dike remains to mark the fissure through which it was injected4 ,,chapter ,,iii4 ,,detailed ,,description ,,of ,,the ,,mountains4 ,,mount ,,ellsworth4 ,it has already been stated that the strata about the bases of the ,henry ,mountains are nearly level2 but the country which is built of them is far from level4 ,the arrangement of the drainage lines has caused the degradation of some parts to greatly exceed that of others1 so that while the district at the south1 which borders the ,colorado ,river1 is paved with the red sandstones of the ,jura-,trias series1 the adjacent region at the north still carries the yellow sandstones and blue shales of the ,cretaceous series4 ,all about ,mount ,ellsworth are the upper strata of the ,jura-,trias4 ,the lower beds of the same series rise upon its flanks and arch over its summit4 ,a description of the structure of the mountain must include1 first1 the arch of the strata2 second1 the faults which modify the arch2 third1 the system of trachyte dikes and trachyte sheets2 and fourth1 the sculpture of the mountain4 ,in its general proportions the arch is at once simple and symmetrical4 ,from all sides the strata rise1 slowly at first1 but with steadily increasing rate1 until the angle of #de is reached4 ,then the dip as steadily diminishes to the center1 where it is nothing4 ,a model to exhibit the form of the dome would resemble a round-topped hat2 only the level rim would join the side by a curve instead of an angle1 and the sides would not be perpendicular1 but would flare rapidly outward 7see ,figure #aa74 ,the base of the arch is not circular1 but is slightly oval1 the long diameter being one-third greater than the short4 ,the length of the uplift is a little more than four miles2 the width a little more than three miles1 and the height about #e1jjj feet4 ,the curvature fades away so gradually at its outer limit that it is not easy to tell where it ends1 and the horizontal dimensions assigned to the dome are no more than rude approximations4 ,but there is another element which can be given more exactly4 ,the line of maximum dip1 which separates the convex upper portion of the dome from the concave periphery1 is easily traced out in nature1 and runs at the foot of the steep part of the mountain4 ,it surrounds an area two miles in width and two and two-thirds miles in length4 ,illustration3 ,,fig4 #aa;,a4--,view from the west spur of ,mount ,ellsworth1 showing the trachyte dikes of the north spur and revetments of sandstone and trachyte4 ,illustration3 ,,fig4 #aa4--,stereogram of ,mount ,ellsworth2 an ideal restoration of the form of the overarching strata4 ,the ,ellsworth arch is almost but not completely isolated4 ,the ,holmes arch1 upon the east side1 stands so near that the bases of the two impinge and coalesce1 and the same thing happens1 though less notably1 with the ,hillers arch at the north4 ,the simplicity of the arch is further impaired by faults--not great faults dividing the whole uplift1 but a system of small displacements which are themselves subordinate phenomena of the uplift4 ,they are restricted to the central portion1 and never occur so low down as the line of maximum dip4 ,the strata of the upper part of the arch are divided into a number of prismoid blocks which stand at slightly different levels but are not sufficiently deranged to destroy the general form of the arch4 ,the greatest throw is only a few hundred feet4 ,all or nearly all of the fault planes are occupied by dikes of trachyte4 ,the trachyte injections are not confined to the fault planes1 nor is their area so restricted as the fault area4 ,dikes and sheets abound from the crest of the dome down to what might be called its springing line--the line of maximum dip4 ,at the center1 dikes are more numerous2 near the limit1 sheets4 ,the central area is crowded so full of dikes1 and the weathering brings them so conspicuously to the surface1 that the softer sedimentaries are half concealed1 and from some points of view the trachyte appears to make the entire mass4 ,the accompanying plan 7,figure #ab7 shows the arrangement of the dikes in one of the outer amphitheaters of the mountain1 where they are less complicated than in the central region4 ,the trends of two spurs 7a b and c d7 are indicated by the hatchings4 ,they join the main crest of the mountain at e1 and inclose between them a deep amphitheater which opens to the west4 ,upon the steep walls of the amphitheater the dikes outcrop in lines of crags1 dividing rough slopes of yellow and purple and brown sandstone4 ,the profile of one of the walls of the amphitheater 7from a to b1 ,figure #ab7 is drawn in ,figure #ac for the sake of exhibiting the relation of the dikes to faulted blocks of sandstone4 ,it will be seen that the throw of the faults is not constantly in one direction4 ,illustration3 ,,fig4 #ad4--,profile of the ,northern ,spur of ,mount ,ellsworth4 #a1 #b1 #c1 #d1 and #e are ,trachyte ,dikes4 ,a1 ,aubrey ,sandstone4 ,s1 ,shinarump ,shale4 ,v1 ,vermilion ,cliff ,sandstone4 ,g1 ,gray ,cliff ,sandstone4 ,the zone of sheets is just inside the line of maximum dip4 ,usually only one or two sheets are laid bare by the erosion1 but at one point 7see ,figure #ad7 four can be counted4 ,toward the center of the uplift all of these are limited by the erosion and exhibit their broken edges4 ,downward1 or toward the periphery1 they dip out of sight4 ,laterally they can be traced along the mountain side for varying distances1 but they soon wedge out and are replaced by others en echelon4 ,in thickness the sheets rarely exceed #ej feet1 and never #ajj4 ,they are always thin as compared to the rock masses which separate them1 but1 by reason of their superior ability to resist erosion1 monopolize a large share of the surface1 and mask a still greater amount with their dbris4 ,illustration3 ,,fig4 #ab4--;,ground plan of ,trachyte ,dikes on the western flank of ,mount ,ellsworth4 ,illustration3 ,,fig4 #ac4--,profile of a western spur of ,mount ,ellsworth1 showing the arrangement of ,dikes and ,faults4 ,the dotted bed is the purple band at the top of the ,vermilion ,cliff ,sandstone4 ,the dikes of trachyte are indicated by letters4 ,the sedimentary rocks are not altered beyond the region of trachyte intrusion4 ,the mere flexure of the strata was not accompanied by a perceptible change of constitution4 ,in the zone of sheets there is little change except along the surfaces of the contact4 ,for a few feet1 or perhaps only a few inches1 there is a discoloration 7usually a decolorization7 and a slight induration1 without notable alteration of minerals4 ,but in the region of reticulated dikes none of the sedimentaries are unchanged2 crystals are developed1 colors are modified1 and hardness is increased1 so that the physical properties of familiar strata no longer serve for their identification4 ,still there is no crumpling4 ,the trachyte masses and the altered rocks in contact with them are so much more durable than the unaltered strata about them that they have been left by the erosion in protuberances4 ,the outcrop of every dike and sheet is a crag or a ridge1 and the mountain itself survives the general degradation of the country only in virtue of its firmer rock masses4 ,nevertheless1 the mountain1 because it was higher than its surroundings1 has been exposed to more rapid erosion1 and has been deprived of a greater depth of strata4 ,from the base of the arch there have been worn #c1ejj feet of ,cretaceous1 and from #ejj to #a1ejj feet of the ,jura-,trias series1 which is here about #c1jjj feet thick4 ,from the summit of the arch more than #b1ejj feet of the ,jura-,trias have been removed4 ,the strata exposed high up on the mountain being older than those at the base1 and the dip being everywhere directed away from the center1 it is evident that the mountain is surrounded by concentric outcrops of beds which lift their escarpments toward it4 ,it is usually the case1 where the strata which incline against the flank of a mountain are eroded1 that the softer are excavated the more rapidly1 while the harder are left standing in ridges2 and an alternation of beds suitable for the formation of a ridge occurs here4 ,one of the upturned beds is the massive ,vermilion ,cliff sandstone1 and beneath it are the shales of the ,shinarump ,group4 ,by the yielding of the shales the sandstone is left prominent1 and it circles the base of the mountain in a monoclinal ridge4 ,but the ridge is of a peculiar character1 and has really no title to the name except in the homology of its structure with that of the typical monoclinal ridge4 ,it lacks the continuity which is implied by the word 8ridge04 ,the drainage of ,mount ,ellsworth is from the center of the dome outward4 ,a half dozen drainage lines originate in the high crests and pass outward through the zone of upturned strata4 ,lower down their interspaces are divided by others1 and when they reach the circling escarpment of the ,vermilion sandstone their number is fifteen4 ,each of these cuts the ridge to its base1 and the effect of the whole is to reduce it to a row of sandstone points circling about the mountain4 ,each point of sandstone lies against the foot of a mountain spur1 as though it had been built for a retaining wall to resist the out-thrust of the spur4 ,borrowing a name from the analogy1 ,i shall call these elementary ridges revet-crags1 and speak of the spurs which bear them as being revetted4 ,the accompanying sketch is designed to illustrate the structure1 but is not drawn from nature4 ,in the view of ,mount ,hillers 7,figure #bg7 the revetments may be seen1 and in the bird's-eye view of the ,henry ,mountains 7,plate ,v71 as well as in the ,frontispiece1 the revet-crags of ,mount ,ellsworth also are portrayed4 ,the diagram of the north spur of ,mount ,ellsworth 7,figure #ad7 shows the revet-crag of that spur at ,v4 ,illustration3 ,,fig4 #ae4--,revet-,crags4 ,the revet-crags of ,vermilion sandstone follow1 in a general way1 the line of maximum dip about the base of ,mount ,ellsworth2 but a few of them rise higher1 and one--that which joins the northwest spur--climbs until it is but little lower than the summit of the mountain4 ,outside the circle of ,vermilion ,cliff sandstone lies the ,gray ,cliff sandstone1 and in a few places it takes the form of a revetment4 ,inside the same circle there are many revetments1 constituted by trachyte sheets bedded in ,shinarump shales 7,figure #ad74 ,conforming perfectly with the strata1 the sheets yield by erosion forms which are identical with those afforded by hard sedimentary beds1 and to the distant eye the impression of the arching structure of ,mount ,ellsworth is conveyed less by what can be seen of the strata than by ascending revetments of trachyte sheets1 which simulate and interpret the strata4 ,illustration3 ,,fig4 #af4--,mount ,holmes1 from the north4 ,the laccolite of ,mount ,ellsworth is not exposed to view1 but ,i am nevertheless confident of its existence--that the visible arching strata envelop it1 that the visible forest of dikes join it1 and that the visible faulted blocks of the upper mountain achieved their displacement while floated by the still liquid lava4 ,the proof1 however1 is not in the mountain itself1 but depends on the association of the phenomena of curvature and dike and sheet with laccolites1 in other mountains of the same group4 ,in the sequel these will be described1 but it chances that the mountain next to be considered is even less developed by erosion than ,mount ,ellsworth4 ,,mount ,,holmes4 ,the order of sequence which places ,mount ,ellsworth before ,mount ,holmes is the order of complexity4 ,the former contains one laccolite1 the latter two4 ,neither of the two is visible1 but the strata which envelop them shadow forth their forms and leave no question of their duality4 ,they are so closely combined that the lesser seems a mere appendage of the greater4 ,from the center of the greater there is a descent of strata in all directions1 but from the center of the lesser the rocks incline toward one-half only of the horizon4 ,where the two convex arches join there is a curved groin--a zone of concave curvature uniting the two convexities4 ,about the compound figure can be obscurely seen a line of maximum dip1 and beyond that the fading of the curves4 ,the curves throughout are so gentle that it was found exceedingly difficult to establish their limits4 ,in a general way it may be said that each of the ,holmes arches is as broad as the ,ellsworth arch1 but the vertical displacement is less4 ,in the formation of the greater ,holmes arch the amount of uplift was #c1jjj feet2 for the lesser arch1 #a1ejj feet4 ,there is no evidence in the forms of the arches which proves one to be older than the other4 ,studying the curves in the field1 ,i could not discover that either arch asserted itself more strongly than the other in their common ground4 ,they seem to meet upon equal terms4 ,still it is probable1 a priori1 that they were formed successively and not simultaneously4 ,the coincidence in time of two eruptions of lava from neighboring vents is no more unlikely than the coincidence of the two irruptions1 and the same principle of least resistance which causes individual laccolitic arches to assume spheroidal forms1 would have given to the compound arch of two laccolites1 coincident in time1 a simple instead of a compound form4 ,assuming that the arches were successive in origin ,i shall in another and more appropriate chapter discuss the problem of their chronological order in the light of their somewhat peculiar drainage system4 ,the lesser arch betrays no dikes nor sheets4 ,the ,vermilion ,cliff sandstone covers it to the top4 ,the greater is crowned by a few grand dikes which govern its topography4 ,from the center a long dike runs to the south1 a short one to the north1 two to the east1 and one to the west4 ,the course of each is a mountain spur1 and between them are amphitheaters and gorges4 ,clinging to the dikes are bodies of altered sandstone1 but the great sandstone masses of the summit were unaltered and from them have been excavated the gorges4 ,along the dike-filled fissures there has been some faulting1 but there is no reason to believe that the displacement is great in amount4 ,toward the flanks of the mountain there are a few sheets1 the outermost of which is far within the line of maximum flexure4 ,their escarpments instead of facing upward like the revetting sheets of ,mount ,ellsworth1 face downward2 their buried and unknown edges are the edges toward the mountain4 ,their thinning toward the periphery of the arch is conspicuous to the eye in many instances1 as is also the thinning of the dikes4 ,another peculiarity of dike form1 one which has since been noted in a number of localities1 was first detected in ,mount ,holmes4 ,it consists in a definite upper limit4 ,the dike so marked is often as even upon its upper surface as an artificial stone wall4 ,the upper surface may be level or may incline toward one end of the dike1 but in either case it is sure to be found parallel to the bedding of the strata which inclose the dike4 ,this fact led to the suspicion1 afterward confirmed by more direct evidence1 that the flat top of the dike was molded by an unbroken stratum of rock bridging across the fissure which the lava filled 7,figure #bj74 ,the converse phenomenon can be observed in the ridge which joins ,mounts ,ellsworth and ,holmes4 ,a great dike there forms the crest of the ridge for half a mile1 its base being buried in sandstone2 but at the end of the ridge the strata are seen to be continuous beneath it 7,figure #ba74 ,illustration3 ,,fig4 #ag4--,stereogram of the ,holmes ,arches2 an ideal restoration of the form of the overarching strata4 ,illustration3 ,,fig4 #ah4--;,ideal cross-section of the ,laccolites of ,mount ,holmes4 ,illustration3 ,,fig4 #ai4--;,a flat-topped dike4 ,illustration3 ,,fig4 #bj4--;,ideal ,cross-section of ,flat-topped ,dikes2 a1 before denudation2 b1 after denudation4 ,illustration3 ,,fig4 #ba4--;,ideal ,cross-section of a ,flat-bottomed ,dike4 ,illustration3 ,,fig4 #bb4--;,diagram to illustrate a hypothetical explanation of ,flat-edged ,dikes4 ,that a fissure several feet or several scores of feet in width should end thus abruptly1 demands explanation1 and the phenomena immediately concerned offer none4 ,nevertheless it is easy to make an assumption which if true renders both cases clear4 ,if we assume that the fissure instead of ending at the crosshead is merely offset1 and resumes its course beyond1 and that the dike contained in it has two bodies connected by a thin sheet 7,figure #bb71 we shall have no difficulty in conceiving the erosion which will produce either of the natural appearances described4 ,the rocks which constitute ,mount ,holmes are the same as those about its base4 ,the ,vermilion ,cliff and ,gray ,cliff ,sandstones alone appear in the crests4 ,the underlying ,shinarump shales are cut by the erosion at a few points only1 and those are near the base4 ,for this reason the ,vermilion ,sandstone is not undermined about the base1 and the circle of revet-crags which surrounds ,mount ,ellsworth finds no counterpart4 ,there are1 indeed1 a few revetments of ,gray ,cliff sandstone1 but they are scattered and for the most part inconspicuous4 ,in the general view of ,mount ,holmes 7,figure #af71 one of the main dikes crowns the nearest spur1 and another the spur leading to the right4 ,at the left are minor dikes1 and high up is a trap sheet notched on its lower edge4 ,at the left base of the mountain lies the lesser arch4 ,figure #bc gives a section exhibited by one of the northward caons4 ,it shows one of the faults of the upper part of the arch and illustrates the thinning of the sheets as they descend4 ,illustration3 ,,fig4 #bc4--,section shown in a northward caon of ,mount ,holmes4 a1 ,vestige of ,trachyte sheet4 b b b1 ,trachyte sheets4 c1 ,trachyte dike4 #a1 ,gray ,cliff ,sandstone4 #b #b1 ,purple ,sandstone4 #c1 ,vermilion ,cliff ,sandstone4 #d1 ,shinarump ,shale4 ,,mount ,,hillers4 ,next in order to the north is ,mount ,hillers4 ,let it not be supposed1 however1 that there is discernible system in the geographic arrangement of the mountains or of the laccolites4 ,a chart of the mountain peaks and a chart of the laccolites would alike prove intractable in the hands of those geologists who draw parallel lines through groups of volcanic vents by way of showing their trend4 ,they are as perfectly heterotactous as they could be made by an artificial arrangement4 ,the diagram 7,figure #bd7 shows the relation of the laccolite groups to each other and to the meridian4 ,the principal mountain summits are indicated by triangles1 and the curved lines inclose areas of disturbance4 ,mount ,hillers and its foot-hills are constituted by a group of no less than eight laccolites1 and a ninth1 the ,howell laccolite1 is conveniently classed with them1 although not contiguous4 ,illustration3 ,,fig4 #be4--;,cross-section of ,mount ,hillers4 ,,fig4 #bf4--,the same1 with ideal representation of the underground structure4 ,scale1 #a inch #d1jjj feet4 #a4 ,tununk ,sandstone2 #b4 ,henry's ,fork ,conglomerate2 #c4 ,gray ,cliff ,sandstone4 ,the full black lines represent trachyte sheets1 and the broad black area the ,hillers ,laccolite4 ,illustration3 ,,fig4 #bg4--,mount ,hillers1 from the south4 ,the ,hillers laccolite is the largest in the ,henry ,mountains4 ,its depth is about #g1jjj feet1 and its diameters are four miles and three and three-quarter miles4 ,its volume is about ten cubic miles4 ,the upper half constitutes the mountain1 the lower half the mountain's deep-laid foundation4 ,of the portion which is above ground1 so to speak1 and exposed to atmospheric degradation1 less than one-half has been stripped of its cover of overarching strata4 ,the remainder is still mantled and shielded by sedimentary beds and by many interleaved sheets of trachyte4 ,the portion which has been uncovered is not left in its original shape1 but is sculptured into alpine forms and scored so deeply that not less than #a1jjj feet of its mass are shown in section4 ,all about the eroded 7south7 face of the mountain the base is revetted by walls of ,vermilion and ,gray ,cliff sandstone1 strengthened by trachyte sheets4 ,at the extreme south these stand nearly vertical 7#hj71 and their inclination diminishes gradually in each direction1 until at the east and west bases of the mountain it is not more than #fj4 ,on the north side there are no revet-crags1 and the inclination is comparatively slight4 ,it would appear that the laccolite was asymmetric1 and was so much steeper-sided on the south that that side suffered most rapid degradation4 ,illustration3 ,,fig4 #bd4--;,ground ,plan of the ,henry ,mountains4 ,the curved lines show the limits of the principal displacements2 the triangles1 the positions of the main peaks4 ,n1 ,mount ,ellen4 ,p1 ,mount ,pennell4 ,h1 ,mount ,hillers4 ,m1 ,mount ,holmes4 ,e1 ,mount ,ellsworth4 ,by reference to the section 7,figure #be7 it will be seen that the sedimentary strata of the north flank stretch quite to the summit of the mountain4 ,the same beds which form the revet-crags on the southern base constitute also some of the highest peaks4 ,since these rest directly upon the laccolite1 it is assumed that the next lower beds of the stratigraphic series form its floor2 and the base of the laccolite is drawn in the ideal section on the level which the ,shinarump ,group holds where it is unaffected by the displacements of the mountain4 ,it is noteworthy that wherever the sedimentaries appear upon the mountain top they are highly metamorphic4 ,but in the revet-crags there is very little alteration4 ,massive sandstone1 divided by sheets and dikes several hundred feet in thickness1 is discolored and indurated at the contact surface only1 and ten feet away betrays no change4 ,the engraving of ,mount ,hillers 7,figure #bg7 exhibits the south face with its revet-crags and bold spurs of trap4 ,in nature the effect is heightened by the contrast of color1 the bright red revetments being strongly relieved against the dark gray of the laccolite4 ,the strata of the summits cannot be discriminated at a distance4 ,they are too near the laccolite in hardness to differ from it in the style of their sculpture4 ,of the minor laccolites of the cluster there are three so closely joined to the chief that they merge topographically with the mountain4 ,they are not well exposed for study4 ,the smallest1 which overlooks the pass between ,mount ,hillers and ,mount ,pennell 7,a1 ,figure #bh7 has probably lost the whole of its cover and with it so much of its substance that the original form and surface cannot be seen4 ,its floor is probably the ,tununk sandstone4 ,east of it and lying a little deeper in the ,cretaceous series is a second laccolite 7,b71 broader1 lower1 and less eroded4 ,the third 7,c7 joins the great one on the northeast1 and is so closely united that it was at first supposed to be the same body4 ,later examinations have shown1 however1 that its immediate roof is the ,henry's ,fork conglomerate1 and its horizon is thus established as more than two thousand feet above that of its great companion4 ,illustration3 ,,fig4 #cj4--,the ,steward ,laccolite4 ,illustration3 ,,fig4 #bh4--;,diagram of the ,hillers ,cluster of ,laccolites2 ,ground plan4 ,illustration3 ,,fig4 #bi4--;,diagram of the ,hillers ,cluster of ,laccolites2 ,elevation4 ,the upper horizontal line marks the base of the ,cretaceous2 the middle1 the base of the ,jura-,trias2 the lower1 the level of the sea4 ,the ,steward laccolite 7,figure #cj7 is better exposed for study4 ,it was buried in the soft bad-land sandstone of the ,flaming ,gorge ,group1 and its matrix has been so far washed away that nearly the whole body of trap is revealed4 ,it is weathered out1 like a chert-nodule on the face of a block of limestone4 ,at one end it is bared quite to the base1 and the sandstone floor on which it rests is brought in sight4 ,the waste of the sandstone has undermined its edge1 and a small portion of the laccolite has fallen away4 ,near the opposite end a fragment of its cover of arching sandstone survives--just enough to indicate that the sedimentaries were once bent over it1 and that the smooth low-arching surface which now crowns it portrays the original form which the molten lava assumed4 ,the laccolite is about two and a half miles long and one and one-half broad4 ,the height of its eastward face1 where it is sapped by the erosion of the bad-land rock1 is six hundred feet1 and the central depth must be more than eight hundred feet4 ,illustration3 ,,fig4 #ca4--;,cross-section of the ,pulpit arch1 with ideal representation of the ,pulpit ,laccolite4 ,scale1 #a inch #c1ejj feet4 #a1 ,vermilion ,cliff ,sandstone4 #b1 #b1 ,gray ,cliff ,sandstone4 #c1 #c1 ,flaming ,gorge ,shale4 #d1 ,henry's ,fork ,conglomerate4 #e1 ,tununk ,shale4 ,pulpit arch is as high and as broad as the lesser arch of ,mount ,holmes1 but its place is not marked in the topography by an eminence for the reason that the degradation of the land has not yet progressed so far as to unearth its core of trachyte4 ,the drainage from ,mount ,hillers crosses it from west to east and has given it an oblique truncation1 as illustrated in the diagram4 ,at the upper end of the slope the ,henry's ,fork conglomerate outcrops2 at the lower end the base of the ,flaming ,gorge series1 and in the interval the ,gray ,cliff sandstone is lifted to the surface4 ,the same streams which planed away the crown of the arch have now cut themselves deeper channels and divide the massive sandstone by picturesque caons1 between which it is grotesquely carved into pinnacles and ridges4 ,a curious salient of the sandstone has given its name to the arch4 ,how deeply the ,pulpit laccolite lies buried is not known1 no sheet nor dike of trachyte betraying its proximity4 ,the valley of the ,colorado may have to be deepened thousands of feet before it will be laid bare4 ,the ,jerry ,butte is the most conspicuous adjunct to ,mount ,hillers and topographically is more important and striking than the features which have just been described1 but its structure is less clear4 ,its crest is formed by a great dike several hundred feet in width and two miles in length1 and with an even top like those observed on ,mount ,holmes4 ,the western end of the dike is the higher and forms the culminating point of the butte1 and from it there radiate three other dikes of notable size4 ,the inclosing strata1 preserved from erosion only by the shelter of the dikes1 are the lower portion of the ,cretaceous series1 and they are so little lifted above their normal level that there is room for no considerable laccolite beneath them4 ,the inclination of the beds is so complicated by the dips of the ,pulpit1 ,steward1 and ,hillers arches1 all of which are contiguous1 that nothing can be made out of the form of the laccolite1 if it exists4 ,the ,howell laccolite lies apart from the cluster and is well exposed4 ,it differs from all that have been enumerated in its extreme thinness4 ,with a breadth of more than two thousand feet1 it has a depth of only fifty4 ,seen from the east1 it might readily be mistaken for a coule1 for on that side it is the thin1 hard1 black cap of a table carved out of soft1 sandy shale 7,flaming ,gorge ,group7 by circumdenudation4 ,but followed westward1 the table is found gradually to lose its height by the rising of the adjacent land1 and at last the lava-bed runs into the slope and disappears beneath the upper layers of the same sandy shale on which it rests4 ,how far it extends under ground can only be conjectured4 ,how far it originally stretched in the opposite direction cannot be known because it is broken away4 ,the original edge is concealed at one end and has been undermined and destroyed at the other1 so that the only place where it can be seen is the point at which it emerges from the shale4 ,at this point1 where erosion has bared but has not yet attacked the lava1 the form and character of the edge are exhibited4 ,in place of the tapering wedge which usually terminates intrusive sheets1 there is a blunt1 rounded margin1 and the lava scarcely diminishes in depth in approaching it4 ,the underlying strata1 locally hardened to sandstones1 lie level2 the overlying curve downward to join them1 and between the curved strata is interleaved a curved lava-sheet4 ,in all these characters the intrusive body is affiliated with the typical laccolites1 and distinguished from the typical sheets4 ,illustration3 ,,fig4 #cb4--,the ,howell ,laccolite1 as seen from the north4 ,illustration3 ,,fig4 #cc4--,the ,edge of the ,howell ,laccolite4 ,illustration3 ,,fig4 #cd4--,mount ,pennell1 from the west4 ,the laccolite which is marked 8,d0 on the diagrams of the ,hillers cluster is identical in nearly all its characters with the ,howell2 it is thin and broad4 ,one margin is wasting as its foundation is sapped2 the other is hidden from view4 ,its depth does not diminish toward the edge4 ,moreover1 a few dikes issue from its margin1 or from beneath its margin4 ,it was intruded within the same formation as the ,howell 7the ,flaming ,gorge shale71 but at a horizon several hundred feet higher2 and1 what is specially noteworthy1 the rock of which it is composed is identical in facies with that of the ,howell laccolite1 and notably different from all others which were observed in the ,hillers cluster4 ,thus there are grouped in this one cluster laccolites of the most varied character1 differing in form1 in magnitude1 in the stratigraphic depth at which they were intruded1 in the extent to which they have been uncovered or demolished in the progress of erosion1 and also1 but very slightly1 in their lithologic characters4 ,the greatest is one thousand times as bulky as the least4 ,the length of the most obese is three times its depth2 the length of the most attenuated is more than one hundred times its depth4 ,the one highest in the strata lies a thousand feet above the base of the ,cretaceous rock series2 the lowest is not higher than the summit of the ,carboniferous4 ,the latter has not yet been touched by erosion1 others have been completely denuded1 and some have been partially demolished and removed4 ,,mount ,,pennell4 ,mount ,pennell and ,mount ,ellen are distinct mountain masses separated by a low pass1 but there is no interval between the clusters of laccolites by which they are constituted4 ,whether the site of a laccolite shall be marked by a mountain depends in great measure on the relation of the laccolite to the progress of erosion4 ,in the ,henry ,mountains the laccolites which have not been reached by the denudation scarcely affect the topography4 ,the arched sedimentaries above them are no harder than the same strata in the surrounding plain1 and they are brought substantially to the same level4 ,it is to those which the downward progress of erosion has reached and passed that the mountains are due4 ,in virtue of their hardness they survive the general degradation1 and conserve with them broad foundations of more perishable material4 ,mounts ,ellen and ,pennell mark the positions of the highest of a great cluster of laccolites1 and the pass between them marks a part of the cluster where all the laccolites lie low in the strata4 ,illustration3 ,,fig4 #ce4--;,cross-section of ,mount ,pennell4 #a1 ,blue ,gate ,sandstone4 #b1 #b1 ,blue ,gate ,shale4 #c1 #c1 ,tununk ,sandstone4 ,the full black lines represent ,trachyte4 ,mount ,pennell is not so easily studied as the lower mountains at the south4 ,its summits are timbered and are carved into alpine forms which do not portray the structure but rather mask it4 ,upon its flanks however the topography and the structure are in so close sympathy that the latter is easily read2 and by their study some of the general features of the mountain have been made out4 ,from the east and south and west the strata can be seen to rise toward it4 ,the uprising strata on the west are the ,tununk sandstone and the shales above and below it4 ,the sandstone forms no revetments1 but accords so closely in its dips with the slopes of the mountain that it is the surface rock over a broad area1 outcropping wherever there is rock exposure4 ,at the head of the foot-slope trachyte sheets are associated with it1 some overlying and others underlying it2 and at one point a gorge reveals a laccolite not far below it--a laccolite that may or may not be the great nucleus of the mountain4 ,on the west and south flanks the uprising strata are the ,blue ,gate and ,tununk sandstones1 with their shales4 ,the ,gate sandstone has been worn away nearly to the foot of the slope1 and forms a monoclinal ridge circling about the base4 ,the ridge is interrupted by a number of waterways1 and it sends salients well up upon the flank1 but it is too continuous to be regarded as a mere line of revetments4 ,the ,tununk sandstone is not to be seen without search1 being covered by heavy trachyte sheets4 ,trachyte sheets also underlie it1 and the whole are carved into a conspicuous series of revet-crags4 ,illustration3 ,,fig4 #cf4--,mount ,pennell1 from the north4 ,the association of overarching strata with sheets of trachyte leaves no doubt in my mind that the core of ,mount ,pennell is laccolitic1 but whether it is simple or compound is not so clear4 ,the collation of all the observed dips shows that if there be but one laccolite it has not the simplicity of form which usually characterizes them4 ,there are low arches of the strata at the southern1 northern1 and northeastern bases1 which reveal no trachyte and give the impression that there may be a foundation of low-lying laccolites upon which the main trachyte mass or masses of the mountain are based4 ,one of these low arches1 that at the northeast1 is shown in the foreground of ,figure #cf4 ,the strata which portray it are of the ,henry's ,fork conglomerate1 and the laccolite which they cover is of necessity distinct from that which is revealed on the east flank of the mountain4 ,illustration3 ,,fig4 #cg4--,sentinel ,butte4 ,in addition to the laccolites of the foundation and of the main body1 there is a series which jut forth from the northern flank like so many dormer windows4 ,they are comparatively small but are rendered conspicuous by the removal of the soft rocks which originally inclosed them4 ,they are higher in the strata than any other observed laccolites1 their position being above the ,tununk sandstone and in the ,blue ,gate shale4 ,the core of the main body of the mountain is probably inclosed in the ,tununk shale1 and the laccolites under the low arches 7at the north at least7 are entirely below the ,cretaceous4 ,the higher series stand on top of the low arches1 and are just outside of the sheets which inclose the central body4 ,the largest of them constitutes ,sentinel ,butte1 and stands guard over ,penellen ,pass4 ,sapped by the yielding of its soft foundation it is rapidly wasting1 and on three sides its faces are precipitous4 ,the huge blocks which cleave from it as they are undermined strew the surrounding slopes for a great distance4 ,its depth of #djj feet is made up of two layers1 of which the lower is the deeper1 and between which there is a slight lithologic difference4 ,the upper surface of the butte is smooth and plane with an inclination to the south4 ,it is probably a portion of the original surface of the laccolite4 ,thus we have in ,mount ,pennell a great central body consisting of a single laccolite or of a number closely massed together2 an inferior group of three or more1 evidenced by low broad arches2 and a superior group of not less than four1 all of which are partially destroyed4 ,,mount ,,ellen4 ,the crest of ,mount ,ellen is as lofty as that of ,mount ,pennell and it is more extended4 ,it stretches for two miles from north to south and is buttressed by many spurs4 ,the sculpture of the crest is alpine1 and the structure is consequently obscured4 ,there are dikes of trachyte and perhaps the remnants of laccolites2 there are ,cretaceous sandstones greatly indurated2 and there are ,cretaceous shales baked to clinking slate2 but they are all carved into smooth1 pyramidal forms1 and each is half hidden by the dbris from the rest so that their order and meaning cannot be seen4 ,the flanks however are full of interest to the geologist4 ,the ,ellen cluster of laccolites is a broad one1 and all but the central portion is well exposed for study4 ,in the spurs and foot-slopes and marginal buttes no less than sixteen individual laccolites have been discriminated1 a number of them most beautifully displayed4 ,they will be enumerated in the order of their position1 beginning at the west of ,penellen ,pass and passing along the western1 northern1 and eastern flanks to the ,scrope ,butte1 east of the pass4 ,illustration3 ,,fig4 #ch4--;,ground ,plan of the ,ellen ,cluster of ,laccolites4 ,in the chart of the ,ellen cluster1 ,figure #ch1 an attempt is made to show the horizontal grouping of the laccolites and the order of their superposition wherever they overlap4 ,it will be observed that where the limits are imperfectly known the outlines are left incomplete1 and that the central area remains blank1 not because it contains no trachyte masses1 but because its alpine sculpture has prevented their study4 ,where it is not evident which of two encroaching laccolites is the superior1 they are separated by a straight line4 ,illustration3 ,,fig4 #dj4--,section of the ,lewis ,creek ,caon through the ,newberry ,arch4 #a1 ,henry's ,fork ,conglomerate4 #b1 ,upper portion of ,flaming ,gorge ,shale4 #c1 ,newberry ,laccolite4 ,the line a a in the chart is the springing line of a broad1 flat arch which underlies all the other arches of the western flank4 ,if it covers but one laccolite1 that one is the rival in magnitude of the ,hillers nucleus1 although widely different in proportions2 but it is more probable that it contains a greater number4 ,the upper surface is rolling and uneven1 and has not the degree of symmetry which laccolites usually display4 ,at the points b1 c1 d1 and e the altitude of the arch is #c1hjj1 #c1ejj1 #b1jjj 7estimated7 and #b1ejj feet4 ,nevertheless there is nothing in its simple outline to indicate a compound structure2 the monoclinal ridges by which it is margined do not exhibit the flexuous curves which are commonly seen about the bases of confluent arches4 ,whether the nucleus is simple or compound it sends no branches to the surface2 the only outcrops of trachyte belong to the overlying arches4 ,the upper parts of the arch have been so carried away that the steepness of the mountain flank is not increased by it1 and inferior strata are brought to the surface4 ,at the north the crown of the arch bears the ,henry's ,fork conglomerate1 while beyond its base the plateau is built of ,blue ,gate sandstone4 ,at the south the arch bears the ,tununk sandstone1 and the ,masuk lies outside4 ,illustration3 ,,fig4 #ci4--,the ,newberry ,arch and ,laccolite4 ,the laccolite marked 8,e0 on the chart rests upon the ,tununk sandstone4 ,the ,blue ,gate shale which once buried it has been all washed away except some metamorphosed remnants upon the top1 and the trachyte itself has wasted to such an extent that its original form cannot be traced4 ,the laccolite has no near neighbor1 and the erosion has left it prominent upon the mountain flank4 ,a continuous and solitary spur joins it to the central ridge4 ,the ,newberry laccolite makes a knob #a1gjj feet high1 and stands by itself4 ,its cover of ,henry's ,fork conglomerate is re-enforced by a number of trachyte sheets1 and is broken through at one point only4 ,at that point ,lewis ,creek cuts with a straight course across a flank of the arch1 and exposes a portion of the nucleus in section 7,figures #ci and #dj74 ,the conglomerate does not rest directly upon the trachyte1 but is separated by one or two hundred feet of shale of the ,flaming ,gorge ,group4 ,illustration3 ,,fig4 #da4--,the ,geikie ,laccolite 7,g71 overlapped by the ,henry's ,fork ,conglomerate 7,h ,h71 and the ,shoulder ,laccolite 7,s74 ,two miles to the northward is the ,geikie laccolite1 smaller than the rest but similar in character4 ,it lies close to the top of the ,flaming ,gorge shale1 and is enwrapped by the ,henry's ,fork conglomerate4 ,upon three sides the conglomerate can be seen to curve over its margin from top to bottom1 and upon two of these sides the curves are so broken through by erosion that the trachyte is visible within4 ,on the north two caons cut down to the nucleus1 and on the south there is a broad face of trachyte framed all about by the cut edges of the conglomerate beds4 ,the ,shoulder laccolite overlaps the ,geikie1 and the two are exposed in such manner as to show their relation in section4 ,the conglomerate runs under the one and over the other and separates them4 ,the upper laccolite is a broad and deep one1 and takes its name from the fact that it makes a great shoulder or terrace on the mountain side4 ,toward the mountain it is buried2 toward the valley it is uncovered1 and in part bounded by a cliff4 ,it is deeply cleft by caons4 ,it has not been subjected to measurement1 but its depth is not overestimated at fifteen hundred feet nor its area at five square miles4 ,in the sketch 7,figure #db7 many of these features can be traced--the ,geikie laccolite at the left and the ,shoulder in the center1 with an outcrop of the conglomerate curving down from the roof of the one to the floor of the other1 and the ,newberry arch in the foreground with its cleft side4 ,at the rear is the pyramidal ,ellen ,peak and the ,f laccolite1 overlooking the ,shoulder4 ,in the distance at the left is the ,marvine laccolite4 ,little more can be said of the ,f laccolite than that it exists and is the nucleus of a lofty spur4 ,its summit rises too nearly to the crest of the mountain to be well defined1 and at its base the sedimentaries are hidden by talus4 ,illustration3 ,,fig4 #db4--,the ,western ,flank of ,mount ,ellen4 ,n1 ,newberry ,arch2 ,s1 ,shoulder ,laccolite2 ,g1 ,geikie ,laccolite4 ,illustration3 ,,fig4 #dc4--,the ,northern face of the ,marvine ,laccolite4 ,illustration3 ,,fig4 #dd4--,the ,western face of the ,marvine ,laccolite4 ,not so the ,marvine laccolite4 ,lying at the foot of the mountain where erosion is so conditioned as to discriminate between hard and soft1 and surrounded by nothing firmer than the ,tununk shale and ,tununk sandstone1 it has suffered a rapid denudation1 in which nearly the whole of its cover has been carried away without seriously impairing its form4 ,it stands forth on a pedestal1 devoid of talus1 naked and alone4 ,the upper surface undulates in low waves preserving the original form as it was impressed on the molten mass4 ,over a portion there is a thin coating of sandstone1 the layer next to the trachyte being saved from destruction by the induration acquired during the hot contact4 ,from the remainder this also has disappeared1 and the contact face of the trachyte is bare4 ,for some reason the exterior portion of the laccolite disintegrates more slowly than the interior4 ,it may be that there was some reaction from the surrounding sedimentaries during the cooling1 which modified the crystallization4 ,or it may be that at a later epoch a reciprocal metamorphism was induced along the contact of the diverse rocks4 ,at all events there is a crust a few feet in thickness which is specially qualified to resist destructive agents1 and which by this peculiarity can be distinguished from the trachyte of the interior4 ,all about the northern and western faces1 which are steep1 this crust has been broken through and the interior excavated2 but it is only along the upper edge of the face that the crust is completely destroyed4 ,along the lower edge it is preserved in remnants sufficiently numerous to fully define the outline of the base4 ,each remnant is a sort of revet-crag standing nearly vertical and joined by a buttress to the cliff behind it4 ,in the accompanying sketches 7,figures #dc and #dd7 the most of these features find better expression than words can give them4 ,the solemn order of the tombstone-like revetments is not exaggerated1 nor is the contrast between the ruggedness of the cliff and the smoothness of the upper crust4 ,at the left in the upper view1 and at the right in the lower1 there can be seen inclined strata1 the remnants of the arch which once covered the whole4 ,the extreme depth of the laccolite is #a1bjj feet1 and its diameters are #f1jjj and #d1jjj feet4 ,the ,g arch1 the ,dana1 the ,crescent1 and the ,maze agree in having no visible laccolites4 ,they are mere dome-like uplifts1 by which inferior beds are brought to light4 ,in the middle of the ,crescent arch1 and there only1 is a small dike4 ,they differ in their dimensions and in their erosion and topography4 ,the ,g arch is low and broad1 and lifts the ,henry's ,fork conglomerate a few hundred feet only4 ,it is covered by that bed except where ,bowl ,creek and one or two others cross it in shallow caons4 ,the ,dana arch bears the same relation to ,mount ,ellen and ,jukes ,butte that the ,pulpit arch bears to ,mount ,hillers4 ,the streams which flow down have truncated it1 and afterward carved a system of caons below the plane of truncation4 ,the ,henry's ,fork conglomerate overlooks it from the base of the ,jukes laccolite on one side1 and on the other margins it with a monoclinal ridge2 and in the interval the ,flaming ,gorge and ,gray ,cliff rocks come to the surface4 ,illustration3 ,,fig4 #de4--,the ,jukes ,butte1 as seen from the southeast1 showing the ,jukes ,laccolite1 resting upon the ,dana ,arch4 ,the ,crescent arch is so perfectly truncated by the existing mountain streams that their flood-plains unite above it in a single broad slope4 ,on the side toward the mountain there are a few insular hills of the conglomerate1 and on the side toward the plateau the same rock lifts a low monoclinal ridge which circles about the base of the arch in a crescent4 ,within the crescent there are few outcrops1 but it is probable that the ,gray ,cliff ,sandstone is brought to the surface4 ,near the center a solitary thin dike juts forth1 like a buoy set to mark the place where a laccolite is sunk4 ,judging the magnitude of the laccolite by the proportions of the uplift1 it has a diameter of nearly four miles and a depth of #b1ejj feet2 and these dimensions indicate a volume of three and a half cubic miles4 ,the ,maze arch covers a smaller area than the ,crescent1 but its height is greater4 ,the drainage from the mountain crosses it on a number of lines1 but there is no indication that at any recent stage of the degradation they have produced an even truncation4 ,at present they divide the ,gray and ,vermilion ,sandstones by so intricate a labyrinth of deep caons that the whole area of the uplift is almost impassable4 ,the monotony of red sandstone1 for here all members of the ,jura-,trias are brick-red1 the variety of dip1 complicated to the eye by oblique lamination1 the multiplicity of caons and ridges1 conspire to give an impression of chaos from whatever point the tract is viewed2 and even from the most commanding stations ,i was unable to make out completely the arrangement of the drainage lines4 ,still no faults were discerned1 and it is probable that the ,maze arch1 intricate as it seems1 is a simple circular dome4 ,on the north it adjoins the ,crescent arch1 and the monoclinal ridges of conglomerate which margin the two at the east are confluent4 ,on the south it adjoins rather more closely one of the low arches which have been referred to the ,pennell cluster4 ,on the west1 or toward the mountain1 it is probably met by other arches at its own level2 but these if they exist cannot be fully known until the progressing degradation of the country shall have removed certain laccolites which lie above them and slightly overlap the ,maze arch4 ,the four arches just described are of the foundation series of the eastern base1 and cover laccolites of unknown depths4 ,higher in the strata1 and at the same time absolutely higher1 is a second series1 which to a certain extent overlap them4 ,the ,bowl ,creek encroaches on the ,g laccolite2 the ,jukes1 on the ,dana and on the ,bowl ,creek2 the ,h laccolite1 on the ,crescent2 the ,peale and ,scrope1 on the ,maze4 ,illustration3 ,,fig4 #df4--;,cross-section of the ,bowl ,creek ,arch4 c1 c marks the water level of ,bowl ,creek2 l1 the ,bowl ,creek ,laccolite2 a1 a1 ,shales2 and s1 the ,gryphea ,sandstone4 ,scale1 #a inch #a1jjj feet4 ,the ,bowl ,creek arch is so masked by the overlapping ,jukes laccolite1 and by the encroachment of certain large dikes1 that its general form and proportions are not known2 but it is laid bare at one point in a fine natural section4 ,bowl ,creek crosses it near the center1 and in the walls of the caon are exhibited two hundred feet of the laccolite1 together with two hundred and fifty feet of superjacent beds4 ,the curve of the strata is unbroken by faults or dikes1 and carries them below the level of the creek at each end of the caon4 ,next above the trachyte lies a clay shale which has been baked to the hardness of limestone4 ,it is one hundred feet thick1 and is more or less altered throughout1 as is also the sandstone which overlies it4 ,the extent of the metamorphism indicates that the trachyte mass by which it was produced is not a mere sheet1 but is the body of the laccolite itself4 ,the ,jukes laccolite encroaches upon the ,g1 the ,dana1 and the ,bowl ,creek arches1 and is superior to them all2 it may be said to stand upon them4 ,the trachyte has a depth of only one thousand feet1 but it lies so high with reference to the general degradation that it is a conspicuous feature of the topography4 ,the edges of the laccolite are all eaten away1 and only the central portion survives4 ,all of its faces are precipitous4 ,the cover of shale or sandstone has completely disappeared1 and the upper surface seems uneven and worn2 but a distant view 7,figure #dg7 shows that its wasting has not progressed so far as to destroy all trace of an original even surface4 ,the eminences of the present surface combine to give to the eye which is aligned with their plane the impression of a straight line4 ,the hill is loftier than the laccolite1 for under the one thousand feet of trachyte are five hundred feet of softer rock which constitute its pedestal1 and by their yielding undermine the laccolite and perpetuate its cliffs4 ,illustration3 ,,fig4 #dg4--,profile of the ,jukes ,butte1 as seen from the northwest4 ,the ,h laccolite is not well exposed4 ,it lies on one edge of the ,crescent arch and is covered by the ,henry's ,fork conglomerate4 ,illustration3 ,,fig4 #dh4--,the ,peale ,laccolite exposed in natural cross-section4 a1 b1 c1 d1 and e are intrusive masses of trachyte4 ,h is the ,henry's ,fork ,conglomerate4 ,illustration3 ,,fig4 #di4--,the ,east ,flank of ,mount ,ellen1 showing the ,scrope1 ,peale1 and ,jukes ,laccolites1 and the ,maze and ,crescent ,arches4 ,little is known of the form of the ,peale laccolite4 ,one edge is lost in the obscurity of the alpine sculpture1 and the other has been removed along with the crest of the ,maze arch1 on which it rested4 ,but by this removal a section has been opened across the laccolite1 revealing its internal structure from top to bottom4 ,it is shown to be composite1 attaining its height of #hej feet by the compilation of three distinct beds of trachyte1 separated by partings and wedges of shale4 ,the lowest bed is thin and of small extent4 ,next is the main bed1 six hundred feet thick and a mile or more broad2 and on top is a bed two hundred feet thick and proportionately narrow4 ,each of the beds is lenticular in section1 and the piling of the less upon the greater produces a quasi-pyramidal form4 ,the interleaved shale bands are metamorphosed to the condition of slate4 ,under the laccolite are one or two hundred feet of shale1 apparently unaltered except at the contact4 ,then come the ,henry's ,fork conglomerate1 #cej feet thick1 and the ,flaming ,gorge shale1 several times thicker4 ,within the upper shale is a restricted trachyte sheet and near the top of the lower shale is a broader one4 ,the latter is double throughout1 its two layers having been intruded at different times4 ,the top of the escarpment is at the top of the laccolite1 and only a short distance back from the brow are shale and sandstone resting upon the trachyte and conforming to its uneven surface4 ,the ,scrope laccolite resembles the ,jukes in everything except that its erosion has progressed so far as to obliterate every trace of the original upper surface4 ,its position in the strata is about the same1 and the erosion of its matrix has left it a conspicuous crag4 ,it rests on the flank of the ,maze arch1 just as the ,jukes laccolite rests on the ,dana arch4 ,the remnant of trachyte is less than one thousand feet high1 and has been carved into a subconical form in which no hint of the original size and proportions of the trachyte body is conveyed4 ,figure #di is a view of the east flank of ,mount ,ellen1 as seen from ,mount ,hillers4 ,it groups together many of the details that have been enumerated4 ,the conical hill at the left is the ,scrope laccolite4 ,the spur from the mountain which ends just at the right of it is the ,peale laccolite4 ,the bold butte which terminates the last spur of the mountain in the distance is the ,jukes laccolite4 ,across the base of the latter one can trace the outcrop of a hard bed4 ,this is the ,henry's ,fork conglomerate1 and the upward curve which it shows belongs 7probably7 to the ,crescent arch4 ,nearer than the ,jukes ,butte and in the same direction is a low hill1 marking the dike within the ,crescent4 ,just to the left of it is an insular outcrop of the conglomerate1 and nearer by is another outcrop in the form of a cliff1 which is continuous to the base of the ,peale laccolite4 ,between the ,peale and ,scrope laccolites the conglomerate is hidden by an embayment of the cliff1 and it reappears in the base of the ,scrope ,butte4 ,in all these outcrops the escarpments of conglomerate face toward the east and at the same time toward the ,maze and ,crescent arches4 ,on the opposite side of the arches the same conglomerate outcrops in a monoclinal ridge with its escarpment facing to the west4 ,the ridge can be traced in the sketch from a point in the foreground under the ,jukes ,butte nearly to the eastern base of the butte1 the course at first being almost directly toward the butte and then curving far to the right and forming the ,crescent4 ,between the ,scrope and ,peale laccolites on one side and the monoclinal ridge on the other1 lie the ,maze and the ,maze arch4 ,beyond the ,maze arch and limited at the right by the ,crescent1 is the ,crescent arch4 ,the ,scrope1 the ,peale1 and the ,jukes are visible laccolites2 the ,maze and ,crescent arches cover invisible laccolites4 ,the determinate laccolites and arches which compose the lower slopes of ,mount ,ellen1 while they are of prime importance for purposes of investigation1 must not be considered superior in number and magnitude to those of the central region4 ,that region is known to abound in trachyte masses1 and it far exceeds the marginal district in the extent and degree of its metamorphism4 ,there is every reason to believe that the mountain crest marks the zone of greatest igneous activity1 and that the foot-hills are as truly subsidiary from a geological point of view as they are from a topographic4 ,there is no evidence of a great central laccolite1 such as the ,hillers and ,pennell clusters possess1 and ,i am disposed to regard the mountain as a great congeries of trachyte masses of moderate size1 separated and in the main covered by shales and sandstones4 ,the sedimentary strata of the summits are all of the ,cretaceous series1 but they are too greatly altered to permit the discrimination of the ,masuk1 ,gate1 and ,tununk groups4 ,the ,henry's ,fork conglomerate1 which might have been recognized even in a metamorphic condition1 was not seen4 ,,stereogram ,,of ,,the ,,henry ,,mountains4 ,for the double purpose of mapping and studying the mountains a model in relief was constructed1 in which great pains was taken to give all the principal features their proper altitudes and proportions4 ,this model was photographed1 and has been reproduced by the heliotype process in ,plate ,,iii1 at the end of the volume4 ,after it had been completed1 a second model was constructed by adding to the surface of the first4 ,wherever the ,blue ,gate sandstone appeared in the original model no addition was made4 ,where the ,tununk sandstone appeared there was added an amount equivalent to the combined thickness of the ,blue ,gate sandstone and the ,blue ,gate shale2 and in general1 enough was added in every part to bring the surface up to the summit of the ,blue ,gate sandstone4 ,in this way a restoration was made of the form of that sandstone previous to its erosion4 ,it is not to be understood that the mountains ever possessed this form2 for when the surface of the ,blue ,gate sandstone was unbroken by erosion it was unbroken only because it was covered by other strata1 which while they shielded it were themselves eroded4 ,if the sandstone had been indestructible1 this is the form which would have been developed by the washing away of all the overlying beds2 and in this form are embodied the arches and domes which were impressed upon the sandstone by the upswelling of the laccolites4 ,the model became a stereogram of the displacements of the ,henry ,mountains1 and a photograph from the stereogram appears in ,plate ,,iv4 ,it will be observed that over the central district of ,mount ,ellen1 where by reason of the peculiar sculpture of the rock its structure was concealed1 the restoration of the sandstone was not carried2 it seemed better to represent our lack of knowledge by a blank than to bridge over the interval by the aid of the imagination4 ,if the reader will study the plate1 he will find that it expresses a great body of the phenomena which have been described in this chapter4 ,the simplicity of the ,ellsworth and ,holmes arches is contrasted with the complexity of the others2 the greatness of the ,hillers and ,pennell domes with the smallness of those which lie upon their flanks4 ,one point that is especially striking is the relation between the upper and lower domes of the ,ellen cluster4 ,the upper1 which give rise to all the conspicuous features of the mountain flanks1 are comparatively small1 while the lower1 which might almost be overlooked in a rapid examination of the mountain1 are comparatively large and constitute the great mass of the uplift4 ,the smaller laccolites1 because they are the upper1 have been denuded of their covers1 and in virtue of their hardness stand forth salient4 ,the larger1 because they are the lower1 have not been laid bare1 and the comparatively feeble resistance which their covers have opposed to erosion has impressed their forms but slightly on the topography4 ,,chapter ,,iv4 ,,the ,,laccolite4 ,the principal facts in regard to the laccolites of the ,henry ,mountains having been set forth in the preceding chapter1 an attempt will now be made to deduce from them the natural history of the ,laccolite4 ,there is a question which the critical geologist will be likely to propound1 and which should be answered at the outset4 8,what evidence01 he may demand1 8is there that the origin of the laccolite was subsequent to the formation of the inclosing strata rather than contemporaneous with it8 ,may it not have been buried instead of intruded8 ,may not the successive sheets and masses of trachyte have been spread or heaped by eruption upon the bottoms of ,mesozoic seas1 and successively covered by the accumulating sediments80 ,the answer is not difficult4 #ast4 ,no fragment of the trachyte has been discovered in the associated strata4 ,the constitution of the several members of the ,mesozoic system in the ,henry ,mountain region does not differ from the general constitution of the same members elsewhere4 ,this evidence is of a negative character1 but if there were no other it would be sufficient4 ,for there is indubitable proof that at the end of the ,shinarump period the ,henry ,mountain region was lifted above the ocean1 and if any of the nuclei of the mountains had then existed they could not have escaped erosion by shore waves1 and must have modified the contemporaneous deposits4 #b;d4 ,the trachyte is in no case vesicular1 and in no case fragmental4 ,if it had been extruded on dry land or in shallow water1 where the pressure upon it was not sufficient to prevent the dilatation of its gases1 it would have been more or less inflated1 after the manner of recent lavas4 ,if it had issued at the bottom of an ocean1 the rapidity of cooling would have cracked the surface of the flow while the interior was yet molten and in motion1 and breccias of trachyte dbris would have resulted4 ,the absence of inflation and of brecciation are of course of the nature of negative evidence1 but they derive weight from the fact that a great number of distinct bodies of trachyte have been examined in the course of the investigation4 #c;d4 ,the inclination of the arched strata proves that they have been disturbed4 ,if the laccolites were formed in each case before the sediments which cover them1 the strata must have been deposited with substantially the dips which they now possess4 ,this is incredible4 ,the steepest declivity of earth-slopes upon the land is #cd from the horizontal1 and they have not been found to equal this under water4 ,prof4 ,j4 ,d4 ,whitney noted #bc as the original slope of a deposit on the ,pacific ,coast1 and regarded it as an extreme case4 ,the writer has made many measurements of the inclination of oblique lamination in massive sandstones1 and found the maximum to be #bd4 ,but the strata which cover the laccolites dip in many places #de to #fj1 and in the revetments of the south base of ,mount ,hillers they attain #hj4 #dth4 ,it occasionally happens that a sheet1 which for a certain distance has continued between two strata1 breaks through one of them and strikes across the bedding to some new horizon1 resuming its course between other strata4 ,every such sheet is unquestionably subsequent to the bedding4 #eth4 ,the strata which overlie as well as those which underlie laccolites and sheets1 are metamorphosed in the vicinity of the trachyte1 and the greatest alteration is found in the strata which are in direct contact with it4 ,the alteration of superior strata has the same character as the alteration of inferior4 ,this could never be the case if the trap masses were contemporaneous with the sediments2 the strata on which they were imposed would be subjected to the heat of the lava1 but the superior strata would accumulate after the heat had been dissipated4 ,in the ,henry ,mountains a large number of observations were made of the phenomena at and near the contacts of sedimentary and igneous rocks1 and in every instance some alteration was found4 ,in fine1 all the phenomena of the mountains are phenomena of intrusion4 ,there is no evidence whatever of extrusion4 ,it is not indeed inconceivable that during the period in which the subterranean chambers were opened and filled1 a portion of the lava found its way to the top of the earth's crust and there built mountains of eruption2 but if such ever existed1 they have been obliterated4 ,the ,henry ,mountains are similar among themselves in constitution4 ,they all exhibit dome-like uplifts2 they all contain intrusive rocks2 and their intrusive rocks are all of one lithologic type4 ,they are moreover quite by themselves2 the surrounding country is dissimilar in structure1 and there is no gradation nor mingling of character4 ,thus similar and thus isolated it is natural to regard the mountains as closely related in origin1 to refer their trachytes to a common source1 and to look for homology in all their parts4 ,it was the search for such homology which led to the hypothesis that the laccolite is the dominant element of their structure4 ,it is now time to examine this hypothesis1 the truth of which has been assumed in the preceding pages1 and see how far it accords with the facts of observation4 ,the facts to be correlated are the following3 #ast4 ,there are seven laccolites which lie so far above the local plane of erosion that they are specially exposed to denuding agents4 ,they have no enveloping strata1 and their only associated sheets lie in the strata under them4 ,their original forms have been impaired or destroyed by erosion4 ,they are the ,scrope1 the ,jukes1 the ,sentinel and its three companions1 and the ,a laccolites4 #b;d4 ,there are two laccolites so nearly bared that their forms are unmistakable1 but which are still partially covered by arching strata1 and which have associated sheets and dikes4 ,they are the ,marvine and the ,steward laccolites4 #c;d4 ,there are five supposed laccolites situated where the erosion planes are inclined1 which run under the slopes and are covered at one side or end1 and at the other project so far above them as to have lost something by erosion4 ,these are accompanied by overarching strata and by sheets and dikes4 ,they are the ,peale1 the ,howell1 the ,shoulder1 the ,d1 and the ,e4 #dth4 ,there are seven or eight supposed laccolites1 of which only a small part is in each case visible1 but which are outlined in form by domes of overarching strata4 ,their bases are not exposed4 ,associated with them are dikes and sheets4 ,they are the ,hillers1 the ,pennell1 the ,geikie1 the ,newberry1 the ,bowl ,creek1 the ,c1 the ,h1 and perhaps the ,f4 #eth4 ,there are five domes of strata accompanied by dikes and 7with one exception7 by sheets1 but showing no laccolite4 ,they are the ,ellsworth1 the ,greater ,holmes1 the ,crescent1 the ,jerry1 and the ,b arches4 #fth4 ,there are nine or more domes of strata with no visible accompaniment of trachyte4 ,they are the ,lesser ,holmes1 the ,pulpit1 the ,g1 the ,dana1 and the ,maze arches1 and those of the foundation of ,mount ,pennell and of the west base of ,mount ,ellen4 ,upon the hypothesis that all these phenomena are examples of the laccolitic structure1 they have the following explanation3 ,each individual case comprised originally a laccolite1 covered by a great depth of uplifted and arching strata1 and accompanied by dikes and sheets which penetrated the strata to a limited distance4 ,lying at different depths from the surface1 they have borne and still bear different relations to the progressive degradation of the country1 and have been developed by erosion in different degrees4 ,in nine of the instances cited the arch of strata has been truncated1 but at so high a level that no dikes nor sheets were unearthed4 ,in five instances the plane of truncation was so low that dikes and sheets were brought to light1 but not the main body of trachyte4 ,the truncation was in most of these cases less perfect because of the resistance to erosion by the hard dikes and sheets and by the strata which their heat had hardened4 ,in eight other instances the erosion has left prominent the dome of hardened strata with its sheets and dikes1 but has somewhere broken through it so as to reveal a massive core of trachyte4 ,in five instances one side of the dome of strata has been washed away1 exposing the core of trachyte to its base and showing undisturbed strata beneath it4 ,in two instances the soft matrix has been so far washed away from the laccolite as to expose its form fully2 and seven laccolites have not only lost all cover but have themselves been partially demolished4 ,certainly1 the hypothesis accords with all the facts that have been observed and unites them into a consistent whole4 ,it explains fourteen dome-like arches of sedimentary rock which are imperfectly exposed1 by classing them with seven other arches of the same region which have been opened in section to the base and found to contain laccolites2 and it strengthens the case by pointing to a connected series of intermediate phenomena4 ,until some strata-dome of the ,henry ,mountains1 or of a closely allied mountain1 shall be found to display some different internal structure1 it will be safe to regard the whole phenomena of the group as laccolitic4 ,form of laccolites4--,as a rule laccolites are compact in form4 ,the base1 which in eleven localities was seen in section1 was found flat1 except where it copied the curvature of some inferior arch4 ,wherever the ground plan could be observed it was found to be a short oval1 the ratio of the two diameters not exceeding that of three to two4 ,where the profile could be observed it was usually found to be a simple curve1 convex upward1 but in a few cases and especially in that of the ,marvine laccolite the upper surface undulates4 ,the height is never more than one-third of the width1 but is frequently much less1 and the average ratio of all the measurements ,i am able to combine is one to seven4 ,the ground plan approximates a circle1 and the type form is probably a solid of revolution--such as the half of an oblate spheroid4 ,internal ,structure4--,of the laccolites which are best exhibited in section1 there are a number which appear to be built up of distinct layers4 ,the ,peale exhibits three layers with uneven partings of shale4 ,the ,sentinel shows two without visible interval4 ,the ,howell shows two4 ,the ,pennell has a banded appearance but was not closely examined4 ,the ,marvine shows at a distance a faint banding1 which near by eludes the eye4 ,no division nor horizontal structure was seen in the ,hillers1 ,jukes1 ,scrope1 or ,steward laccolites1 but observation was not sufficiently thorough to satisfy me of its absence4 ,it is probable that all the larger laccolites are composite1 having been built up by the accession of a number of distinct intrusions4 ,there is little or no prismatic structure in the trachytes4 ,it is sometimes simulated by a vertical cleavage induced in sheets and laccolites which are undergoing disintegration by sapping1 but ,i did not observe the peculiar prismatic cleavage which is produced by rapid cooling in dikes1 sheets1 and coules of basalt4 ,the two structures are not often discriminated1 but they are really quite distinct1 and their peculiar characters are easily recognized4 ,the cleavage planes produced by cooling are as a rule perpendicular to the cooling surface1 and the systems of prisms which are based on the opposite walls of a dike or sheet1 do not correspond with each other1 and do not run across1 but meet midway in a confused manner4 ,the cleavage planes which are produced by the shearing force when a massive bed of trap or other rock is undermined or sapped and yields under its own weight1 extend from base to top1 and are perpendicular to the plane of the horizon instead of the plane of the bed4#b ,footnote #b3 ,see page #agb of the 8,exploration of the ,colorado ,river01 by ,j4 ,w4 ,powell4 ,vertical ,distribution4--,the range of altitudes at which laccolites have been formed is not less than #d1ejj feet1 and neither the upper nor the lower limit is known4 ,the highest that are known--those which were intruded at the highest geological horizon--are near the base of the ,blue ,gate shale 7,middle ,cretaceous71 but it is quite possible that higher ones have been obliterated by erosion4 ,the lowest that is known was intruded in the ,shinarump shale1 but it is known of the invisible ,ellsworth laccolite that upper ,carboniferous strata lie above it1 so that its horizon of intrusion must be still lower4 ,the plexus of dikes and sheets on the ,ellsworth arch indicates that the laccolite is not deeply buried2 but in the series of arches there are nine which show no trachyte1 and we have no data from which to infer their depth4 ,how the laccolites are distributed within these limits is more readily comprehended by the aid of a diagram4 ,in ,figure #ej the triangles mark the horizons of determined laccolites1 and the crosses the horizons which the invisible laccolites cannot exceed4 ,for example1 the base of the ,scrope laccolite is visible and is seen to lie on the ,tununk shale #djj feet above the ,henry's ,fork conglomerate2 to represent it a triangle is placed at about the middle of the space representing the ,tununk shale1 and in the column devoted to the ,ellen cluster4 ,the upper surface of the ,geikie laccolite is visible and upon it rest1 first a few feet of ,flaming ,gorge shale1 and then the ,henry's ,fork conglomerate2 to represent it a triangle is placed near the top of the ,flaming ,gorge space4 ,the crown of the ,pulpit arch has been so far eroded that half of the ,vermilion ,cliff sandstone is shown in section1 but no laccolite is revealed4 ,it is evident that the ,pulpit laccolite is lower than the middle of that sandstone2 and to represent it a cross is placed below the middle of the ,vermilion ,cliff space and in the column devoted to the ,hillers cluster4 ,illustration3 ,,fig4 #ej4--;,diagram of the ,vertical ,distribution of the ,laccolites of the ,henry ,mountains4 ,the first feature which this graphic assemblage yields to the eye is that there are at least two zones of laccolites4 ,the upper ranges from the lower part of the ,blue ,gate ,group1 through the ,tununk and ,henry's ,fork1 to the upper part of the ,flaming ,gorge ,group4 ,the lower has not yet been fully developed by erosion1 but its proximity is indicated4 ,the ,hillers laccolite is uncovered at top1 and the dikes of the ,ellsworth1 the ,greater ,holmes1 and the ,crescent have been reached4 ,all of the invisible laccolites indicated in the ,vermilion ,cliff and ,shinarump spaces must be referred to this zone2 and there is reason to suspect that all but one of the invisible laccolites whose indication falls in the ,tununk and ,flaming ,gorge spaces belong also to the lower zone4 ,however this may be1 it is not probable that the determination of the depths of the invisible laccolites would vitiate the conclusion that there is an upper zone of laccolitic frequency which is separated from a lower zone by an interspace of laccolitic infrequency4 ,another feature illustrated by the diagram is that all the determined laccolites are inclosed by soft beds4 ,they have been intruded into the shales1 but not the sandstones4 ,they cluster about the ,henry's ,fork conglomerate1 but none of them divide it4 ,this selection of matrix is confined however to the laccolites and is not exercised by sheets and dikes4 ,trachyte sheets were seen within the ,henry's ,fork1 the ,gray ,cliff1 the ,vermilion ,cliff1 and the ,aubrey sandstones4 ,a third feature of the diagram is the restriction of the upper zone of laccolites to the northward clusters2 ,mounts ,ellsworth and ,holmes contain laccolites of the lower zone only4 ,this fact of distribution is correlated with a fact of denudation--namely1 that in the general degradation of the country1 the region about the southern mountains has lost two thousand feet more than the northern4 ,one fact is probably the cause of the other4 ,the absence of laccolites of the upper zone at the south may have permitted the greater degradation2 or the greater degradation may have caused the destruction of several of the upper laccolites4 ,the fact that the difference in degradation can be independently accounted for is favorable to the latter supposition4 ,the ,colorado ,river which is the main artery of drainage for the whole region1 flows close to the bases of the southern mountains1 and the rapid declivity from the mountain summits to the river has given and still gives exceptionally great power to the agents of erosion4 ,no other cause is needed to explain the difference of degradation1 and the absence of laccolites of the upper zone is explicable without assuming that they were never present4 ,the negative objection to the idea that the southern mountains originally possessed laccolites of the upper zone being thus disposed of1 it is worth while to inquire whether there is any evidence in its favor4 ,if superior laccolites existed1 they would be sure to leave behind them a record of the conduits through which their lava was injected4 ,a dike or a chimney must always connect a laccolite with the source of its material2 and the removal of the laccolite necessarily exposes a cross-section of its stem4 ,the discovery of such a dike can be regarded1 not indeed as a proof of the former existence of a superior laccolite1 but as demonstrating its possibility4 ,the summits and flanks of ,mounts ,holmes and ,ellsworth bear many dikes1 which have been regarded as subsidiary features of the laccolites beneath them1 but it is quite possible that any one of them formerly led to another laccolite above4 ,the upper laccolite may have been first formed and then have been lifted1 dike and all1 when the lower was intruded2 or it may have been last formed1 and been fed through a fissure which traversed the lower after its congelation4 ,the only dike which was discovered in the vicinity of these mountains1 without being upon them1 stands midway between them4 ,it is the only observed dike of the ,henry ,mountains 7excepting always the alpine district of ,mount ,ellen71 which is not so closely associated with some laccolite as to seem an accessory feature1 and its exceptional position has led to the suspicion that it belonged to an overlying laccolite4 ,upon such uncertain evidence no positive conclusion can be based1 and it is vain to build laccolites in the air4 ,the most that can be said is that the southern mountains need not be distinguished from the northern1 because at the present stage of degradation they contain laccolites of the lower zone only4 ,the ,material of the ,laccolites4 ,the intrusive rocks of the ,henry ,mountains were sampled with care4 ,specimens were selected which had undergone little decomposition and which represented all the prominent lithologic varieties4 ,they were chosen from the trachytes of both zones and of each of the mountain masses2 and they represent dikes and sheets1 as well as laccolites4 ,from about thirty specimens thin slices were cut for microscopic examination4 ,captain ,c4 ,e4 ,dutton1 of ,omaha1 ,nebraska1 was so kind as to undertake the study of the collection1 and the letter which embodies his conclusions is given below4 ,in accordance with his diagnosis ,i shall call the intrusive rocks porphyritic trachyte2 and ,i am glad to have the weight of his authority in support of my belief that all the rocks of the series are of one type1 their resemblances far outweighing their differences4 ,,note4--,persons desiring to examine the ,henry ,mountain trachytes under the microscope can obtain mounted thin sections from ,mr4 ,alexis ,a4 ,julien1 ,school of ,mines1 ,columbia ,college1 ,new ,york4 ,,report ,,on ,,the ,,lithologic ,,characters ,,of ,,the ,,henry ,,mountain ,,intrusives4 ,,by ,,captain ,c4 ,e4 ,,dutton4 8,i have examined with great interest and attention the ,henry ,mountain rocks you sent me1 and proceed to acquaint you with such results as my limited facilities have permitted me to derive from the examination4 ,it is a very well defined series1 having some marked characters which distinguish it from the nearest allied group with which ,i am acquainted4 ,this is all the more interesting1 because ,i am inclined to think that these peculiarities may have a definable association with or relation to the manner in which the intrusive rocks occur in those 8laccolites01 as you term them4 8,the hand specimens show in most cases large and unusually perfect crystals of orthoclase imbedded in a very compact uniform paste through which hornblende is also disseminated rather more abundantly than is usually the case where the dominant felspar is monoclinic4 ,micaceous crystals appear to be wholly wanting and this is a notable circumstance1 since the trachytes of the ,plateau country1 to which these rocks are most nearly allied1 are seldom without one or more of them4 ,the only other mineral which is of frequent occurrence in the specimens is magnetite 7or possibly titanic iron71 which is diffused in the usual form of minute granules in many of them1 but is scarce in several of them4 ,in general there is a great scarcity of mineral species and any others than those mentioned are of the greatest rarity4 8,the dominant felspar is orthoclase1 but a portion of it is triclinic1 and ,i presume this portion is albite1 with an occasional occurrence of oligoclase4 ,the groundmass in which the crystals are included is in most cases decidedly compact and without distinguishable crystals1 but shows between the crossed ,nicols closely aggregated luminous points1 which with a -inch objective are resolved indistinctly into felspar4 ,in some cases the crystals of the groundmass are quite apparent with an inch objective1 and their species determinable4 ,but the greater portion of the groundmass is quite amorphous1 and does not polarize light at all4 ,the proportion of crystalline to amorphous matter in the paste is highly variable--in some cases it is quite bright between crossed ,nicols1 in others far less so1 and in none is it entirely dark4 ,those specimens which have the finer and more amorphous groundmass have the larger and more perfect crystals of felspar--an association of properties which is not wholly without qualification1 but still sufficiently decided4 8,turning to the included felspars1 their mode of occurrence is quite an uncommon one1 ,i believe1 so far as the eruptive rocks of the ,rocky ,mountain region are concerned1 and give rise to some hesitation before assigning them definitely to the trachytic group4 ,in a great many cases the felspathic crystals are well developed1 and so large and so nearly perfect that their aspect is decidedly porphyritic4 ,this is especially the case with the dikes of ,mounts ,ellsworth and ,holmes 7,nos4 #ef1 #fa1 #fh1 and #fi74 ,the orthoclase is invariably of the white 8milky0 variety1 with the exception of a single specimen from a ,mount ,ellsworth dike 7,no4 #eg71 where it is present as sanidin4 7,this is an exceptional rock in all respects1 and will be spoken of hereafter47 ,nearly all of them appear to have been subject to alteration by chemical action since their formation as is indicated by their diminished power to polarize light4 ,whether this is due to atmospheric weathering or to changes en masse it is of course impossible to distinguish with certainty1 though ,i incline to the latter view since it is manifested as decidedly in specimens which show no external indications of weathering as in those which do show them4 ,it is not uncommon to find crystals which have almost entirely ceased to polarize4 ,the zonal arrangement is very common in the crystals1 and some of the zones contain numberless minute fluid cavities in the largest crystals4 ,the foreign substances included in the crystals present no novelty1 being the ordinary films of hornblende1 minute needles of felspar1 granules of magnetite1 and those dust-like points of brownish yellow color which are the proper inclusives of the groundmass4 8,the orthoclase occasionally presents the adular variety1 but this never becomes a marked feature4 ,i have observed the same in many of the trachytes of the ,high ,plateaus and of the ,great ,basin4 ,another phenomenon is the occurrence of crystals which are quite typically monoclinic at one end 7orthoclase71 and at the other end have the arrangement of plagioclase4 ,this is well known elsewhere1 and described by ,zirkel4 7,mik4 ,beschaff der ,mineralien u4 ,gesteine74 8,in classifying these rocks therefore1 we may observe that they present a blending of the characteristics which are common to trachyte and felsitic porphyry4 ,those who regard porphyry as a distinct class of eruptive rocks would have no hesitation in calling ,nos4 #ah1 #ef1 #fa1 #fh1 and #fi undebatable felsitic porphyries1 and to the same series might with propriety be added ,no4 #cc4 ,with equal confidence ,nos4 #af1 #bj1 #ce1 and #dc may be called unqualified trachytes4 ,the other rocks are intermediate in character between these two extremes1 and the whole may be regarded as a series in which the individuals form a graduated scale4 8,you will recall the fact that many lithologists object to the terms porphyry or porphyritic being used to designate a distinct class or group of rocks1 holding that they merely characterize a single feature which is more or less frequently presented by all igneous rocks and having no necessary relation to any of them1 and that this is no more adequate to such an important distinction than the color or relative degree of fineness or coarseness of texture4 ,although this latter view seems to me to underrate the distinctive value of the porphyritic character in general1 ,i incline very decidedly to the belief that it is true as applied to these ,henry ,mountain rocks4 ,here at least the porphyritic character has but little significance4 ,in some varieties the crystals are larger and more perfect and the groundmass more homogeneous2 in others the crystals are smaller and imperfect1 and the groundmass more coarse and irregular2 while still others are #8betwixt and between'4 ,the most careful scrutiny fails to show any fundamental differences in the groundmass or in the included minerals4 ,hence ,i think these rocks would be accurately designated as a group by calling them porphyritic trachytes4 ,such varieties as ,nos4 #af1 #bj1 and #ce may by themselves be called simply trachyte1 the porphyritic character being insufficiently distinct in them to warrant any qualification of the name4 8,there is one specimen 7,no4 #eg1 from dike in ,shinarump shale1 ,mount ,ellsworth7 which constitutes an exception to the foregoing4 ,by inspection of a hand specimen it might hastily pass for a very compact andesite1 but the observer will be instantly undeceived by applying the microscope4 ,it consists of imperfect crystals1 which must be sanidin1 imbedded in a very close groundmass composed of a material which differs from the foregoing trachytes in being wholly amorphous4 ,between crossed ,nicols the paste transmits no light whatever1 though between the parallel ,nicols it closely resembles the others4 ,the hand specimen is very dark colored 7gray71 but the slide is sufficiently translucent4 ,the felspar crystals are either fragmental or very imperfectly developed as to their edges and angles1 but polarize very sharply4 ,the amount of twinning is very small1 but it appears occasionally4 ,the rock is undoubtedly a trachyte1 but an unusual one4 ,its dark color is not due to hornblende nor to magnetite1 both of which occur in it very sparingly1 especially the former4 8,i have already remarked that the only frequent minerals besides felspar are hornblende and magnetite4 ,apatite occurs and is tolerably plentiful in a few of the specimens1 but absent from most of them4 ,the crystals are all small1 requiring a low power for the determination of the larger and a high power for the smaller4 ,they present no peculiarities4 ,of very rare occurrence is nepheline4 ,this mineral is usually associated with the more basic volcanic rocks and seldom penetrates the trachytic group4 ,quartz is almost equally rare4 ,the absence of any great variety in the mineral species is quite normal1 except possibly the total absence of mica1 which is usually present and frequently the only associate of felspar in the western trachytes4 ,the ,henry ,mountain rocks do not so far as ,i can discover contain a trace of it4 8,in answer to your particular inquiries-- 8#ast4 #8,is the paste vesicular1 or is there any evidence in the crystals to indicate the pressure under which they were formed8' ,i can only say that the paste is extremely compact and contains no vesicles even in those specimens of which the aspect is most decidedly trachytic4 ,some of the larger crystals of felspar contain an abundance of pores or vesicles which may have contained liquids1 but with a -inch objective they are too small for treatment by the method you refer to4 ,a few large cavities1 usually of irregular shape1 occur1 but ,i am quite unfamiliar with the practical treatment of this subject and cannot advise you4 ,i do not find any cavities still containing fluids1 and ,i presume that even if they existed they would be difficult if not impossible to gauge on account of the impellucidity of the felspar4 ,i presume quartz is the most favorable mineral for this investigation on account of its transparency and the greater frequency of its large cavities4 ,quartz however is almost the scarcest of the contents of these rocks4 8#b;d4 #8,do any mineralogic differences correlate with the superficial or geographic distribution of the rocks8' and 8#c;d4 #8,do any mineralogic differences correlate with the vertical distribution of the trachytes8' ,as it appears from your account of the distribution of the masses that the upper zone belongs 7with one exception7 to ,mounts ,ellen and ,pennell and the lower to the other mountains1 the answer to one is the answer to both1 and this is in the negative4 ,the mineralogical differences are exceedingly small1 considering the number of distinct masses1 and this covers the inquiry entirely4 ,regarding the texture or habitus1 on the contrary1 it appears to me that the true trachytes predominate in the upper zone and the porphyries in the lower1 but not without exceptions4 8#dth4 #8,do any mineralogic differences correlate with the size of the intrusive masses8' ,no mineralogical differences thus correlate1 but ,i find a preponderance of the porphyritic texture in the smaller masses and of the trachytic texture in the larger4 ,it is not without exception1 and the preponderance is small40 ,metamorphism and ,contact ,phenomena4--,wherever the trachytes came in contact with the sedimentaries the latter were more or less altered4 ,large bodies of trachyte produced greater changes than small4 ,the laccolites both metamorphosed their walls more completely1 and carried their influence to a greater distance than the sheets and dikes4 ,the summits of the laccolites had a greater influence than the edges2 a phenomenon to which ,i shall have occasion to revert4 ,the sandstones were less affected than the shales1 at least in such characters as readily catch the eye4 ,clay shales were indurated so as to clink under the hammer1 and ,captain ,dutton discovered with the microscope that minute crystals of felspar had been developed4 ,sandstones were usually modified in color1 and their iron was segregated so as to give a mottled or speckled appearance to the fracture4 ,they were indurated1 but the granular texture was always retained4 ,the trachyte carries numerous small fragments of sedimentary rock broken apparently from its walls1 and these are as thoroughly crystalline as their matrix4 ,the altered rocks are usually jointed1 but nothing approaching to slaty cleavage was seen1 nor has there been any crumpling4 ,the reciprocal influence of the sandstone and shale upon the trachyte was small4 ,specimens broken from the contact surface of a laccolite and from its interior cannot be distinguished4 ,in the ,marvine laccolite however there is a difference between the exterior and interior portions in their ability to withstand erosion4 ,historical4--,before leaving the subject of the structure of the mountains it is proper to place on record certain observations by others which antedated my own but have never been published4 ,while ,professor ,powell's boat party was exploring the caons of the ,colorado1 ,mr4 ,john ,f4 ,steward a geologist and member of the party climbed the cliff near the mouth of the ,dirty ,devil ,river and approached the eastern base of the mountains4 ,he reported that the strata had in the mountains a quaquaversal dip1 rising upon the flanks from all sides4 ,the following year ,prof ,a4 ,h4 ,thompson then as now in charge of the geographic work of ,professor ,powell's survey crossed the mountains by the ,penellen ,pass and ascended some of the principal peaks4 ,he noted the uprising of the strata about the bases and the presence of igneous rocks4 ,in #ahgc ,mr4 ,e4 ,e4 ,howell at that time the geologist of a division of the ,wheeler ,survey traveled within twelve miles of the western base of the mountains1 and observed the uprising of the strata4 ,my own observations were begun in #ahge1 at which time a week was spent among the mountains4 ,they proved so attractive a field for investigation that in the following year a period of nearly two mouths was devoted to their study4 ,other ,igneous ,mountains4--,the ,henry ,mountains are not the only igneous group which the ,plateau province comprises4 ,they are scattered here and there throughout its whole extent4 ,from the summits of the ,henry ,mountains one can see the ,sierra ,la ,sal ninety miles to the northeastward1 and the ,sierra ,abajo seventy miles to the eastward4 ,beyond them and two hundred miles away are the ,elk ,mountains of ,colorado4 ,fifty miles to the southwestward stands the ,navajo ,mountain on the brink of the ,colorado2 and one hundred and twenty miles to the southeast the ,sierra ,la ,lata and the ,sierra ,carriso are outlined against the horizon4 ,westward it is less than thirty miles to the ,aquarius ,plateau1 the nearest member of the great system of volcanic tables among which the ,sevier and ,dirty ,devil ,rivers rise4 ,beyond the horizon at the south and southwest and southeast are a series of extinct volcanoes2 ,mount ,taylor and the ,marcou ,buttes in ,new ,mexico2 the ,sierra ,blanca1 the ,sierra ,mogollon1 the ,san ,francisco ,group and the ,uinkarets in ,arizona2 and the ,panguitch ,lake ,buttes in ,utah4 ,of the groups which are visible1 all but that of the ,aquarius ,plateau are allied in character to the ,henry ,mountains4 ,the ,sierra ,abajo was studied in #ahei by ,dr4 ,j4 ,s4 ,newberry1 geologist of the ,macomb ,expedition1 who writes3 8,within the last few weeks we have been on three sides of this sierra1 and have learned its structure quite definitely4 ,it is a mountain group of no great elevation1 its highest point rising some #b1jjj feet above the ,sage-plain1 or perhaps #i1jjj feet above the sea4 ,it is composed of several distinct ranges1 of which the most westerly one is quite detached from the others4 ,all these ranges1 of which there are apparently four1 have a trend of about #be east of north1 but being arranged somewhat en echelon1 the most westerly range reaching farthest north1 the principal axis of the group has a northwest and southeast direction4 ,the sierra is composed geologically of an erupted nucleus1 mainly a gray or bluish-white trachyte1 sometimes becoming a porphyry1 surrounded by the upheaved1 partially eroded1 sedimentary rocks4 ,the ,lower ,cretaceous sandstones and ,middle ,cretaceous shales are cut and exposed in all the ravines leading down from it1 while nearly the entire thickness of the ,cretaceous series is shown in spurs which1 in some localities1 project from its sides2 apparently the remnants of a plateau corresponding to1 and once connected with1 the ,mesa ,verde4 ,whether the ,paleozoic rocks are anywhere exposed upon the flanks of the ,sierra ,abajo ,i cannot certainly say1 though we discovered no traces of them4 ,it is1 however1 probable that they will be found in some of the deeper ravines1 where1 as in most of these isolated mountains composed mainly of erupted material1 they are doubtless but little disturbed1 but are buried beneath the ejected matter which has been thrown up through them4 8,the relations of the ,cretaceous rocks to the igneous nucleus of the ,sierra ,abajo are very peculiar1 for1 although we did not make the entire circuit of the mountain mass1 and ,i can1 therefore1 not speak definitely in regard to the western side1 as far as our observations extended we found the sedimentary strata rising on to the trachyte core1 as though it had been pushed up through them40 7,geology of the ,macomb ,expedition1 page #ajj47 ,of another group ,dr4 ,newberry says in the same report 7page #ic73 8,of the composition of the ,sierra ,la ,sal we know nothing except what was taught by the drifted materials brought down in the caons through which the drainage from it flows4 ,of this transported material we saw but little1 but that consisted mainly of trachytes and porphyry1 indicating that it is composed of erupted rocks similar to those which form the ,sierra ,abajo1 of which it is in fact almost an exact counterpart4 ,from the cliffs over ,ojo ,verde we could see the strata composing both the upper and second plateaus1 rising from the east1 south1 and southwest on to the base of the ,sierra ,la ,sal1 each conspicuous stratum being distinctly traceable in the walls of the caons and valleys which head in the sierra4 ,it is evident1 therefore1 that the rocks composing the ,colorado ,plateau are there locally upheaved1 precisely as around the ,sierra ,abajo 99 99 9940 ,these mountain groups have been since visited by the geologists of ,dr4 ,hayden's survey1 ,dr4 ,a4 ,c4 ,peale ascending the ,sierra ,la ,sal and ,mr4 ,w4 ,h4 ,holmes the ,sierra ,abajo4 ,mr4 ,holmes has also examined the ,la ,lata and ,carriso ,mountains and found in them the same upbending of ,cretaceous strata and the same association of igneous material4 ,the ,navajo ,mountain has been viewed by ,mr4 ,howell and by the writer from a commanding position on the opposite side of the ,colorado ,river1 and fragments of its trachyte have been gathered on the river bank by ,professor ,powell1 but no geologist has yet climbed it4 ,still there can be no question of its general structure4 ,it is a simple dome of ,jura-,triassic sandstone1 springing abruptly from a plateau of the same material1 and veined at the surface by sheets and dikes of trachyte--the counterpart in fine of ,mount ,ellsworth1 only of more imposing proportions4 ,the ,la ,sal1 the ,abajo1 the ,la ,lata1 the ,carriso1 the ,navajo1 and the ,henry ,mountains agree in their essential features4 ,structurally they have no trends4 ,their phenomena are grouped about centers and not axes4 ,in all of them the strata are lifted into dome-like arches1 and associated with these arches are bodies of trachyte4 ,the trachytes are all of one lithologic type1 and are so closely related that a collection of rock specimens representing all the groups would show scarcely more variety than a collection representing the ,henry ,mountain laccolites4 ,with so many characters in common they can hardly fail to agree in the possession of laccolitic nuclei4#c ,footnote #c3 ,while these pages are passing through the press a paper by ,dr4 ,a4 ,c4 ,peale 8,on a peculiar type of eruptive mountains in ,colorado0 7,bulletin ,u4 ,s4 ,geol4 ,sur41 ,vol4 ,,iii1 ,no4 #c7 comes to hand4 ,he groups together as of one type not only the ,elk1 ,la ,sal1 ,abajo1 ,la ,lata1 and ,carriso ,mountains1 but also the ,spanish ,peaks1 ,park ,view ,mountain1 ,mount ,guyot1 ,silverheels ,mountain1 the ,san ,miguel ,mountains1 the ,la ,plata ,mountains1 and certain smaller masses in ,middle ,park and near the ,huerfano ,river4 ,he says1 8,although modified in several instances1 the general plan appears to be the same4 ,the igneous material came up through fissures in the sedimentaries1 sometimes tipping up their ends1 and sometimes passing through without disturbing them4 ,on reaching the ,cretaceous shales1 it generally spread out in them1 and pushed into and across them dikes and intrusive sheets of the same igneous rock4 ,the elevation in some cases appears to be due to actual upheaval caused by the eruptive force4 ,the mountains as they now exist are doubtless largely the result of erosion1 the hard igneous rock opposing greater resistance to erosive influences than do the surrounding soft sedimentary beds40 ,the ,elk ,mountains are at the very margin of the plateau1 and geographically might be connected with the ,sawatch ,range which bounds the plateau province on that side4 ,but structurally they are a group instead of a range1 and affiliate with the groups which are insulated by an environment of tables4 ,thanks to the labors of ,mr4 ,holmes and ,dr4 ,peale their general structure is known4 ,the ,eastern ,elk ,mountains consist of four great bodies of 8eruptive granite01 over which are arched not only ,mesozoic but ,paleozoic strata4 ,their foundation must be a floor of ,archan metamorphics4 ,two of them1 the ,snow ,mass and ,white ,rock laccolites1 are joined by a continuous line of disturbance1 in the description of which by pen and pencil ,mr4 ,holmes has made an important contribution1 not only to dynamical geology1 but to the methods of geological illustration4 ,the others are more symmetric and are complementary illustrations of the common structure4 ,one1 the ,sopris1 is half truncated by erosion so that the core is exposed at top with an encircling fringe of upturned sedimentaries2 and the other1 the ,treasury1 retains a complete arch of ,paleozoic strata4 ,the ,western ,elk ,mountains are a cluster of smaller laccolites which are inserted between strata of ,cretaceous age4 ,their traps include porphyritic trachytes undistinguishable from those of the ,henry ,mountains1 and eruptive granites identical with those of the ,eastern ,elk ,mountains2 and they exhibit a gradation from one to the other4 ,indeed the two rocks are nearly related1 and their assignment to classes so diverse as trachyte and granite is merely an illustration of the imperfection of our classification of rocks4 ,the description of the ,elk ,mountains will be found on pages #fa to #ga and #afc to #afh of the ,annual ,report for #ahgd of the 8,geological and ,geographical ,survey of the ,territories40 ,if we turn now to the distinctively volcanic mountains of the ,plateau province--to those which are built by eruption at the surface--we leave at once the porphyritic trachytes4 ,mount ,san ,francisco1 ,mount ,bill ,williams1 ,mount ,sitgreaves1 ,mount ,kendrick1 ,mount ,floyd and the ,sierra ,blanca 7of ,arizona7 are all composed of basic trachytes1 and so are the ,aquarius ,plateau and the many tables that lie beyond it4 ,the ,mogollon group1 the ,marcou ,buttes1 the minor cones about ,mount ,san ,francisco1 the ,uinkarets1 and the ,panguitch ,lake group are basaltic4 ,in each of these instances the igneous rock issued above the surface and there is no evidence by displacement that any portion of it was deposited below4 ,mount ,taylor may be an exception4 ,in the character of its lava and its general features it resembles ,mount ,san ,francisco1 but there are disturbed strata on its southern flank1 and it is possible the mountain is both extrusive and intrusive4 ,extrusion and intrusion are probably combined in some small tables lying fifty miles north of the ,henry ,mountains4 ,they are built of ,flaming ,gorge shale1 preserved from erosion by dikes1 sheets1 and 7probably7 outflows of basalt4 ,combining all these facts we attain to a simple relation between two types of igneous rock on the one hand1 and two types of mountain structure on the other4 ,one type of rock is acidic1 including 8porphyritic trachyte0 and 8eruptive granite01 and its occurrence is without exception intrusive4 ,the other type of rock is basic1 including basic trachyte and basalt1 and its occurrence is almost uniformly extrusive4 ,it is not possible to combine the two groups of phenomena by saying that in one case the eruptive cones cover laccolites1 and in the other the laccolites have been covered by eruptive cones which have disappeared2 first1 because many of the eruptive cones are too well exposed to admit of the concealment of laccolitic arches beneath them2 second1 because the two types of lava are essentially different4 ,the acidic type if extruded at the surface would be an ordinary trachyte2 the basic type if crystallized under pressure would be classed with the greenstones4 ,the basis for the generalization is exceedingly broad4 ,i have enumerated only seven groups of laccolitic mountains and ten groups of eruptive2 but with few exceptions each group is composed of many individuals1 each one of which is entitled to rank as a separate phenomenon4 ,in the ,uinkaret ,mountains ,professor ,powell has distinguished no less than one hundred and eighteen eruptive cones1 and in the ,henry ,mountains ,i have enumerated thirty-six individual laccolites4 ,in one locality basic lava has one hundred and eighteen times risen to the surface by channels more or less distinct1 instead of opening chambers for itself below4 ,in the other locality porphyritic trachyte has thirty-six times built laccolites instead of rising to the surface4 ,if our attention was restricted to these two localities we might as naturally correlate the types of structure with some accidents of locality as with types of lava2 but when all the localities are taken into account it is evident that there is no common mark by which either the laccolitic or the volcanic are distinguished4 ,,the ,,question ,,of ,,cause4 ,we are now ready to consider the question3 ,why is it that in some cases igneous rocks form volcanoes and in other cases laccolites8 ,it is not necessary to broach the more difficult problem of the source of volcanic energy4 ,we may assume that molten rock is being forced upward through the upper portion of the earth's crust1 and disregarding its source and its propelling force may restrict our inquiry to the circumstances which determine its stopping place4 ,let us further assume1 but for a moment only1 that the cohesion of the solid rocks of the crust does not impede the upward progress of the fluid rock1 nor prevent it from spreading laterally at any level4 ,the lava will then obey strictly the general law of hydrostatics1 and assume the station which will give the lowest possible position to the center of gravity of the strata and lava combined4 7#a7 ,if the fluid rock is less dense than the solid1 it will pass through it to the surface and build a subarial mountain4 7#b7 ,if the upper portion of the solid rock is less dense than the fluid1 while the lower portion is more dense1 the fluid will not rise to the surface but will pass between the heavy and light solids and lift or float the latter4 7#c7 ,if the crust be composed of many horizontal beds of diverse and alternating density1 the fluid will select for its resting place a level so conditioned that no superior group of successive beds1 including the bed immediately above it1 shall have a greater mean specific gravity than its 7the fluid's7 own2 and that no inferior group of successive beds1 including the bed immediately beneath1 shall have a less mean specific gravity than its own4 ,illustration3 ,,fig4 #ea4--;,diagram to illustrate the application of the law of ,hydrostatic ,equilibrium to the movements of lavas4 ,the shaded bands represent heavy strata2 the open1 light4 ,in the diagram1 a series of light and heavy beds are represented in section by open and shaded spaces4 ,a lava stream free to move upward or laterally will intrude itself at some point 7c7 so placed that every combination of superior beds 7a71 which includes the lowest1 shall have a less average density2 and every combination of inferior strata 7b71 which includes the highest1 shall have a greater average density than that of the lava4 ,the first case is that of a volcano2 the second is that of a laccolite2 and the third is the general case1 including the others and applying to all volcanoes and laccolites4 ,conversely we may say that1 given a series of strata of diverse and alternating density1 a very light lava will traverse it to the top and be extruded2 a heavier will intrude itself at some lower level2 and a series of dissimilar lavas may select an equal number of distinct levels4 ,it is easy to imagine such a balancing of conditions that a slight change in a lava will determine a great change in its level of intrusion4 ,having seen the general application of the hydrostatic law1 it is time to recall the condition which we laid aside at the start4 ,cohesion1 or rigidity1 is never absent and must affect every phase of vulcanism4 ,it certainly opposes the free circulation of lavas1 and it cannot but modify their obedience to the hydrostatic law4 ,but granting this1 and believing that a full comprehension of the subject must include this condition1 ,i am at a loss to tell in what way it influences the selection by a lava flood of a subarial or a subterranean bourne4 ,whether it will on the whole oppose upward progress more than lateral1 or vice versa1 is not clear4 ,if it resists lateral intrusion the more strongly1 it favors the formation of volcanoes2 if it resists upward penetration the more strongly1 it favors the formation of laccolites2 and in either case the working of the hydrostatic law is modified4 ,but in neither case is the working of the law more than modified4 ,the law is not abrogated1 and in obedience to it light lavas still tend to rise higher than heavy however much the rising of all lavas may be hindered or favored4 ,in brief1 since lavas are fluids they are subject to the law of fluid equilibrium1 and their behavior is conditioned by the relations of their densities to the densities of the solids which they penetrate2 and since the latter solids are rigid and coherent1 it is further conditioned by the resistance which is opposed to their penetration4 ,when the resistance to penetration is the same in all directions1 the relation of densities determines the stopping place of the rising lava2 but when the vertical and lateral resistances are unequal1 their relation may be the determining condition4 ,if we can decide whether the determinative condition in the ,plateau region was that of densities or that of penetrability1 we shall have solved our problem4 ,assuming1 first1 that the essential condition is that of penetrability1 we should expect that some particular stratum or that a few particular strata1 being less penetrable than others1 would check the rising lavas and accumulate them in a system of laccolites1 which would occupy one1 or a few definite horizons4 ,volcanoes would occur in districts from which such impenetrable strata either were originally absent or had been removed before the igneous epoch2 and we should expect to find the same variety of material in laccolites and in volcanoes4 ,assuming1 second1 that the essential condition is that of densities1 we should expect as before to find certain stratigraphic horizons more favorable than others to the accumulation of laccolites1 and we should also expect to find certain lavas usually volcanic and certain others usually laccolitic4 ,that is to say--since the condition of impenetrability resides in the solid rock only1 and the condition of density pertains to both solid and fluid1 either condition might determine laccolites at certain stratigraphic horizons1 while the latter only could discriminate certain lavas as intrusive and others as extrusive4 ,the vertical distribution of laccolites is not inconsistent with either assumption4 ,in the ,henry ,mountains there are two zones of occurrence2 in the ,eastern ,elk ,mountains there is a third2 and it is probable in the present state of our knowledge that all other laccolites of the ,plateaus can be assigned to one or another of these4 ,the fact that the laccolites of the upper zone have a vertical range of two thousand feet is rather favorable to the idea that their stations were determined by relations of density1 but is not decisive4 ,when however we turn to the relation between the constitutions and the behaviors of lavas1 we find the entire weight of the evidence in favor of the assumption that conditions of density determine the structure4 ,the coincidence of the laccolitic structure with a certain type of igneous rock is so persistent that we cannot doubt that the rock contained in itself a condition which determined its behavior4 ,we are then led to conclude that the conditions which determined the results of igneous activity were the relative densities of the intruding lavas and of the invaded strata2 and that the fulfillment of the general law of hydrostatics was not materially modified by the rigidity and cohesion of the strata4 ,having reached this conclusion it is natural to seek for confirmation by the investigation of the densities of the rocks concerned in the phenomena4 ,as will appear by a table given further on1 the density of the ,henry ,mountain trachyte has been determined to be #b4fa42 but the densities of the erupted lavas of the ,plateaus are not yet known4 ,there can be no doubt however that the latter are heavier4 ,von ,cotta in his ,lithology gives #b4i to #c4a as the density of basalt1 and #b4f to #b4i as the density of the more basic trachytes4 ,and in general1 it is well established that where the state of aggregation is the same1 basic igneous rocks are always heavier than acidic4 ,but in order that the laccolitic structure should have been determined by density1 the acidic rock of the laccolites must have been heavier in its molten condition than the more basic rocks of the neighboring volcanoes2 and since in the crystalline condition the acidic is the lighter1 it follows that it has gained less density in cooling than the basic4 ,if the amount of contraction of the several rocks in passing from their natural molten condition to the crystalline condition could be determined experimentally1 a crucial test would be applied to our conclusions as to the origin of laccolites4 ,the matter is however beset with difficulties4 ,bischof attempted by melting eruptive rocks in clay crucibles to obtain their ratios of expansion and contraction1 but his method involved so many sources of error that his results have been generally distrusted4 ,he concluded that the contraction in passing from the molten to the crystalline state is greater in acidic than in basic rocks4 ,delesse by an extended series of experiments in which crystalline rocks were melted and afterward cooled to glasses1 showed that acidic rocks increase in volume from #i to #aa per cent4 in passing from the crystalline state to the vitreous1 while basic increase only #f to #i per cent4 ,mallet concluded from some experiments of his own that the contraction of rocks in cooling from the molten condition is never more than #f per cent41 and that it is greater with basic than with acidic rocks2 but considering that the substances which he treated were artificial and not natural products1 that his methods were not uniform1 and that he ignored the distinction between the vitreous and the crystalline1 of which ,delesse had demonstrated the importance1 no weight can be given to his results4 ,if however all of these experiments were trustworthy and their results were concordant1 their bearing upon the problem of the laccolites would still be slight4 ,it is generally conceded that the fusion of lavas is hydrothermal1 while in all the experiments recourse was had to dry fusion2 and the densities attained in the two ways are necessarily different4 ,the practical difficulty in the way of restoring the natural molten condition is great and may be insuperable1 but unless it shall be overcome we cannot learn experimentally the changes of density which igneous rocks undergo in congelation4 ,there is a fact of observation which tends to sustain the view that the laccolitic rocks contracted less in cooling than the volcanic4 ,the prismatic structure is produced by the contraction of cooling rocks during and after solidification4 ,that it does not occur in the ,henry ,mountain trachytes indicates that their contraction was small4 ,that it does occur at numerous localities in ,utah in basalts1 indicates that their contraction was relatively great4 ,mr4 ,jukes1 in his ,manual of ,geology1 says that it is most frequently exhibited in 8doleritic lavas and traps1 being especially characteristic of basalt1 but occurs almost as perfectly in some greenstones and felstones02 and in the range of my own observation ,i can recall no instance of its occurrence in other than basic rocks4 ,for the sake of comparing the densities of the intrusive rocks with those of the strata which contain them1 a number of determinations were made of the specific gravities of specimens representative of the trachytes and of the several sedimentary groups of the ,henry ,mountains4 ,trachytes were selected to represent as great a variety of locality and relation as possible1 and at the same time exclude all specimens which showed traces of decomposition4 ,hand specimens weighing from one hundred to four hundred grains were used1 and these were weighed first dry1 and then suspended in water4 ,by using such large quantities averages were obtained of a rock which1 minutely considered1 is heterogeneous2 and by using the blocks entire instead of pulverized or granulated1 the state of aggregation of its minerals was included as an element of the specific gravity of the rock4 ,it will be observed that the range1 #b4ed to #b4ff1 is very small4 ,table of ,specific ,gravities of ,trachytes of the ,henry ,mountains4 ,locality4 ,specific gravity4 ,east flank of ,mount ,pennell2 sheet #b4ff ,marvine ,laccolite2 north base of ,mount ,ellen #b4fe ,peale ,laccolite2 east flank of ,mount ,ellen #b4fd ,dike on ,mount ,ellsworth #b4fd ,south base of ,mount ,hillers2 sheet #b4fc ,sheet under the ,peale ,laccolite #b4fb ,scrope ,laccolite2 southeast base of ,mount ,ellen #b4fj ,bowl ,creek ,laccolite2 northeast base of ,mount ,ellen #b4eh ,north spur of ,mount ,pennell2 dike #b4eh ,sentinel ,laccolite2 north base of ,mount ,pennell #b4ed -------- ,mean #b4fa ,specimens to represent the stratigraphic series were selected at the margins of the disturbed region so far as possible1 to avoid the effect of metamorphism4 ,but as it was not practicable to eliminate this source of error in every case1 the densities of highly metamorphic specimens were also measured for the purpose of indicating the effect of the metamorphism4 ,in order to restore so far as practicable the condition of the rocks at the time of the lavic intrusion1 the specimens were saturated with water1 and in this condition were weighed in air as well as in water4 ,the results for the porous sandstones are from one-seventh to one-fourteenth lower than would have been obtained by the usual method4 ,hand specimens were used as before4 ,table of ,specific ,gravities of ,sedimentary ,rocks of the ,henry ,mountains4 ,rock4 ,condition4 ,specific gravity4 #a,masuk ,sandstone ,unaltered #b4af #b;,blue ,gate ,sandstone ,unaltered #b4ad #c;,blue ,gate ,shale ,unaltered #b4de #d;,flaming ,gorge ,shale ,unaltered #b4db #e;,gray ,cliff ,sandstone ,unaltered #b4ac #f,vermilion ,cliff ,sandstone1 7top7 ,unaltered 787 #b4ba #g,vermilion ,cliff ,sandstone1 7base7,unaltered 787 #b4bh #h;,henry's ,fork ,conglomerate ,slightly altered #b4be #i,vermilion ,cliff ,sandstone1 ,altered #b4dh #aj;,aubrey ,sandstone ,altered #b4ee #aa,tununk ,shale ,altered #b4fj ,it is plain from this table that the effect of the metamorphism was to increase the densities of the rocks affected4 ,the ,blue ,gate shale which unaltered gave #b4de1 is lithologically identical with the ,tununk shale which altered gave #b4fi4 ,the ,aubrey sandstone cannot be observed unaltered in the vicinity of the mountains1 but at a distance of forty miles where it again comes to the surface it closely resembles the ,gray ,cliff sandstone4 ,if it has the same normal weight as the latter1 then it has increased from #b4ac to #b4ee4 ,the specimens of the ,vermilion ,cliff sandstone numbered #f and #g were not visibly changed1 but as they were obtained from the flank of the ,holmes arch there was reason to suspect that their condition was not normal1 and the determined densities strengthen the suspicion4 ,judged by other localities1 the normal density of the ,vermilion ,cliff rock is not far from that of the ,gray ,cliff rock1 namely #b4ac2 and it is easy to believe that the upper portion of the bed where it lay on the side of the ,holmes arch was changed in density to #b4ba2 while the lower portion lying nearer the laccolite was changed to #b4bh2 and while the same bed among the ,ellsworth dikes acquired the density of #b4dh4 ,taking into account both these considerations and certain others which need not be enumerated1 ,i derive the following3 ,table of the ,specific ,gravities of the ,henry ,mountain ,sedimentary series in the ,order of ,superposition4 ,bed4 ,specific gravity4 ,masuk ,sandstone #b4af ,masuk ,shale estimated #b4dj ,blue ,gate ,sandstone #b4ad ,blue ,gate ,shale #b4de ,tununk ,sandstone #b4ae ,tununk ,shale estimated #b4de ,henry's ,fork ,conglomerate #b4be ,flaming ,gorge ,shale #b4db ,gray ,cliff ,sandstone #b4ac ,vermilion ,cliff ,sandstone estimated #b4ae ,shinarump ,shale estimated #b4dj ,aubrey ,sandstone estimated #b4ae ,taking into account the thicknesses of the several beds enumerated in the foregoing table1 it is easy to obtain the mean specific gravity of all which lie above a given horizon2 and by making this determination for the horizon of the base of each of the indicated beds1 the following table has been derived4 ,the figures are based on the assumption that the rock series included nothing above the ,masuk sandstone4 ,if 7as is probable7 there were ,tertiary beds also1 the estimates are too low1 for the ,tertiaries of the vicinity are calcareous and argillaceous and consequently dense4 ,table showing the ,mean ,specific ,gravities of the ,rock ,series contained between certain horizons and the summit of the ,masuk ,sandstone4 ,horizons4 ,specific gravities4 ,base of ,masuk ,sandstone #b4af ,base of ,masuk ,shale #b4bh ,base of ,blue ,gate ,sandstone #b4bc ,base of ,blue ,gate ,shale #b4cb ,base of ,tununk ,sandstone #b4ca ,base of ,tununk ,shale #b4cd ,base of ,henry's ,fork ,conglomerate #b4cc ,base of ,flaming ,gorge ,shale #b4cf ,base of ,gray ,cliff ,sandstone #b4cc ,base of ,vermilion ,cliff ,sandstone #b4cb ,base of ,shinarump ,shale #b4cc ,from this it appears that the laccolites of the upper zone1 extending from the lower part of the ,blue ,gate ,shale to the upper part of the ,flaming ,gorge ,shale1 bore loads of which the mean densities were from #b4ca to #b4cd1 and that laccolites of the lower zone1 which has its upper limit in the ,shinarump ,shale1 bore loads of which the mean densities were #b4cb and upward4 ,if the positions of the laccolites were determined purely by the law of hydrostatic equilibrium1 then these figures define the density of the molten trachyte1 and show that its contraction in cooling--from the density #b4cd to the density #b4fa--was about one-tenth of its volume4 ,,the ,,stretching ,,of ,,strata4 ,it has been the opinion1 not only of the writer but of other students of the displacements of the ,west1 that the ordinary sedimentary rocks1 sandstone1 limestone1 and shale1 are frequently elongated as well as compressed by orographic movements1 and that this takes place without any appreciable metamorphism2 but it is difficult to find opportunity for the demonstration of the phenomenon by measurement4 ,when a fold is made in a level stratum1 either of two things may take place2 the portions of the stratum which remain level at the sides may approach each other2 or the stratum may be stretched4 ,but when a circular portion of a continuous level stratum is lifted into a quaquaversal arch 7as illustrated in ,figure #aa71 an approach of the level portions is out of the question1 and there must be a stretching or a fracture4 ,of the unfractured quaquaversals of the ,henry ,mountains there is one which combines all the essentials of a crucial case4 ,the ,lesser ,holmes arch is nearly isolated2 on three sides it rises from the undisturbed plateau1 and on the fourth it joins a similar but fractured dome4 ,the major part of its surface is composed of one bed1 the ,vermilion ,cliff sandstone1 broken only by erosion4 ,comparing the length of this bed in its present curved form with the space it must have occupied before it was upbent1 ,i find that in a distance of three miles it has been elongated three hundred feet4 ,moreover there is every reason to suppose that the elongation was produced quickly1 or at least by a succession of finite rather than infinitesimal increments2 for the lifting of the arch was caused by the intrusion of a laccolite1 and though the latter may have been built by the addition of many separate lava flows1 it could not have risen with secular and continuous slowness4 ,the molten trachyte1 rising through a passage and into a reservoir that were comparatively cool1 would have clogged itself by congelation had it not moved with a certain degree of rapidity4 ,illustration3 ,,fig4 #eb4--;,cross-section of an uplifted dome4 ,the dotted lines show the original position of a bed2 the curved lines1 the imposed4 ,the condition which rendered possible the elongation and the sudden bending of so rigid and brittle a rock as a massive sandstone1 was pressure4 ,at the time of the uplift the sandstone was buried by other sediments to a depth of from five thousand to eight thousand feet1 and sustained a pressure of from five thousand to eight thousand pounds to the square inch4 ,now the experiments which have been made upon building stones show that the weight required to crush similar sandstones in a dry condition1 is three thousand to five thousand pounds to the inch2 and it is a fact familiar to quarrymen that sandstone and limestone which are quarried below the water level are both softer and weaker while they are still saturated than they are after drying4 ,so we may fairly assume that the ,vermilion sandstone was loaded at the time of its displacement with a crushing weight4 ,no part could yield to the pressure while it was sustained by the surrounding parts2 but every part was ready to yield whenever its support was withdrawn4 ,it was in a quasi-plastic state and abhorred a fissure as strongly as 8nature abhors a vacuum01 and for the same reason4 ,a fissure could not be opened in it unless it was coincidently filled by something--such as lava--which would resist the tendency of its walls to flow together4 ,the formation of a gaping fissure being thus prevented1 and the uplifting of the dome requiring that the sandstone should cover a greater area1 an extension of the bed was the necessary result4 ,it was not stretched into the dome form2 it was compressed4 ,the efficient force did not act in the direction of the extension1 but vertically4 ,the sandstone was pushed1 not pulled4 ,if this explanation is the true one1 then it is true in general that just as for each rock there is a crushing weight1 so there is for each rock a certain depth at which it cannot be fissured and can be flexed4 ,the softer rocks are plastic at small depths4 ,fire-clays under coal seams exude1 or 8creep01 even with the pressure of a few feet of superincumbent strata4 ,springs of water rise at the outcroppings of soft strata because the joints which intersect most rocks near the surface of the ground cannot cross those which are soft enough to yield under the pressure incident to them4 ,if the soft beds were jointed they would not intercept percolating water1 and the distribution of springs would be very different4 ,the phenomena of fissure veins are in point4 ,when a fault takes place1 and one rock mass is slidden past another to which it had been joined it is usually the case that the opposed surfaces no longer fit together as they did before the movement1 and interspaces are left4 ,these become filled1 at first by water1 and afterward by minerals deposited from the water1 and the mineral masses thus deposited are called fissure veins4 ,but the preservation of the interspaces depends upon the rigidity of the rocks which inclose them2 and it frequently happens that where a system of rocks is traversed by a fault1 the harder will keep somewhat apart and maintain a fissure1 while the softer will be crushed together without an interspace4 ,if the mineral vein which forms in such a fissure is afterward explored in mining1 it is found to be traceable and continuous so far as it is walled by the hard rock upon both sides1 but when the hard is replaced by the soft in one or both walls1 the vein is either reduced to a mere fillet or disappears completely4 ,if the fault extends to a great depth1 it will finally reach a region where the hardest rocks which it separates are coerced by so great a pressure that they cannot hold themselves asunder1 but are forced together before the fissure can be filled by mineral deposits4 ,thus there is a definable inferior limit to the region of vein formation2 and even while it is impossible to assign a downward limit to the fault which made place for a vein1 it may be possible to assign a downward limit to the vein itself4 ,accordant with this view is the absence of fissure veins from the ,henry ,mountains4 ,displacement and thermal disturbance are usually regarded as the conditions of mineral concentration2 and here were displacement and lavic intrusion coincident in time and place4 ,the heat which metamorphosed great bodies of shale and sandstone was surely competent to excite the currents and reactions which concentrate minerals in veins2 but the displacements did not open fissures1 and the heated water could circulate only through the pores of rocks4 ,fissure veins were impossible1 and the sluggish currents which were engendered in continuous rock masses did not effect a great change in the distribution of minerals4 ,,the ,,conditions ,,of ,,rock ,,flexure4 ,there are three known conditions under which strata of the most rigid character may be bent without fracture2 or in other words there are three ways in which flexibility may be either induced or demonstrated4 ,at ordinary temperatures and at the surface of the earth a hard stratum cannot be quickly flexed4 ,but no rigidity is absolute1 and a constant strain1 even though slight1 will in the course of time produce deformation4 ,the same result may be accomplished quickly if the temperature of the stratum is raised to near the point of fusion4 ,or it may be accomplished with neither great heat nor great time if only the stratum is so deeply buried that the weight of its cover keeps it from opening fissures4 ,the three conditions of flexure are time1 heat1 and pressure2 and whenever the circumstances of a displacement include none of these1 the rocks are broken4 ,a fourth condition1 moisture1 is of great importance as an accessory1 but alone it is not sufficient to prevent fracture4 ,the whole body of strata of the earth's crust is saturated with water1 except a very little at the surface1 and all rock movements are thereby facilitated4 ,if the strata were dry1 their flexure would require much more time1 or heat1 or pressure1 than is necessary in their moist condition4 ,often the three conditions complement each other2 but not always4 ,we may say1 the greater the load which strata bear the more rapidly they can be flexed2 and conversely1 the more slowly strata are displaced the less the pressure necessary to prevent fracture4 ,and we may say1 the higher the temperature of strata the more rapidly they can be flexed2 and conversely1 the more slowly strata are displaced the lower the temperature necessary to prevent fracture4 ,for both these statements we find support in a great series of homologies4 ,but we cannot affirm that such a reciprocal relation exists between the effects of heat and pressure4 ,for all rocks are believed to expand by heating1 up to the point of fusion2 and it is a recognized physical law that in all bodies which heat expands1 the effects of heat are opposed by pressure4 ,hence we cannot say1 8,the heavier the load which strata bear the lower the temperature necessary to prevent fracture01 nor can we say1 8,the higher the temperature of strata the less the load necessary to prevent fracture04 ,,the ,,question ,,of ,,cover ,,and ,,the ,,question ,,of ,,age4 ,it is evident that the laccolites of the ,henry ,mountains were formed beneath the surface of the earth's crust1 but at what depth is not so evident4 ,the problem is involved with the problem of the age of the laccolites1 and the two are connected with the general history of the ,basin of the ,colorado4 ,neither problem can be called1 for the present at least1 determinate1 but it is possible to narrow them down by the indication of limits which their solutions will not exceed4 ,so much of the ,colorado ,plateau region as lies within ,colorado and ,utah was covered during a geological age which it is convenient to call ,cretaceous1 by a sea1 the waters of which appear to have become fresh toward the last4 ,then came elevation both general and differential4 ,a great part of the sea bed became dry land1 and the accumulated sediments together with many which underlay them were bent into great waves thousands of feet in altitude4 ,the crests of the waves were subjected to erosion and truncated4 ,then came a second submergence which was purely lacustrine4 ,in some way that has not been ascertained a lake basin was formed1 and the region received a new system of sediments which it is convenient to call ,tertiary1 and which not merely filled the troughs between the great rock-waves but covered the truncated summits of the waves themselves4 ,then followed the desiccation of the basin by the cutting down of its rim where the water overflowed4 ,the overflowing river as it deepened its channel and gradually lowered the lake1 steadily extended its upper course to follow the receding shore2 and finally when the basin was completely drained the river remained1 its channel leading through what had been the deepest part of the ,tertiary sea4 ,that river is the ,colorado4 ,as portions of the lake bottom were successively drained they began at once to be eroded1 and from that time to this there has been progressive degradation4 ,the regions nearest to the central river were reduced most rapidly and have been completely stripped of their ,tertiary strata1 but broad areas of the latter remain at the west1 and north1 and east4 7,the reader will understand that this succinct history is shorn for the sake of clearness of all details and qualifications4 ,there have been complicating eruptions and displacements or oscillations at every stage1 and if the full story could be told1 it would not be by a single paragraph nor by a single chapter47 ,when the ,cretaceous strata were thrown into waves the site of the ,henry ,mountains remained in a trough1 and it probably was not dried1 but continued the scene of sedimentation while the crests of the surrounding rock-waves were worn away4 ,certainly it was not greatly eroded at that time2 and when the ,tertiary lake beds were thrown down it was favorably disposed for a heavy deposit4 ,it is not extravagant to assume that four thousand feet of lake beds rested on the ,masuk sandstone at the beginning of the final desiccation4 ,in brief there may be distinguished-- #a4 ,the deposition of the ,cretaceous4 #b4 ,the folding and erosion of the ,cretaceous4 #c4 ,the deposition of the ,tertiary4 #d4 ,the desiccation of the ,tertiary lake basin4 #e4 ,the erosion which is still in progress4 ,it is evident that the laccolites were not formed until the ,cretaceous strata had been deposited2 for their uplifts have bent and tilted all ,cretaceous rocks up to and including the ,masuk sandstone4 ,they were not formed at any late stage of the final erosion1 for they conserve tables along their western base1 which but for their shelter would long since have disappeared4 ,from the end of the ,cretaceous period to the end of the desiccation of the basin there is no event with which the laccolites can be directly connected4 ,there is however a consideration which in an indirect way sanctions the opinion that the epoch of igneous activity was after the deposition of the ,tertiaries and before their erosion4 ,the ,masuk ,sandstone is at once the summit of the ,cretaceous and the highest bed in the present ,henry ,mountain section4 ,if it were restored over the entire range1 the laccolites of the upper zone would have on the average thirty-five hundred feet of cover1 and those of the lower zone nearly seven thousand feet4 ,this was the depth of their original cover1 if they were intruded at the close of the ,cretaceous age4 ,during the epoch of ,tertiary deposition and the subsequent epoch of erosion1 the cover first increased in depth and then diminished1 having its maximum at the end of the ,tertiary deposition4 ,if it can be shown that the original cover of the upper laccolites exceeded thirty-five hundred feet1 the question of age will be reduced to comparatively narrow limits4 ,in order to discuss the problem of the original depth of cover it will be necessary to consider another matter1 of which the connection will not at first be apparent4 ,the size of laccolites4--,it is a matter worthy of note that no laccolite of inconsiderable extent is known in the ,henry ,mountains4 ,the smallest which has been measured is more than half a mile in diameter1 and the largest about four miles4 ,the phenomenon does not occur upon a small scale1 but has a definite inferior limit to its magnitude4 ,let us seek an explanation of this limit4 ,the dome of strata which covers a laccolite has for its profile on every side a monoclinal curve4 ,in ,figure #eb the section of a dome exhibits a monoclinal flexure in s a and again in s b2 and the dome being approximately circular this flexure completely surrounds it4 ,we may even describe or define the dome as a monoclinal flexure encircling a point or a space4 ,considering now that when the laccolite was injected the overlying strata were lifted1 and that this disturbance was communicated upward to the then existing surface of the earth1 we may properly speak of the lifted body of rock as a cylinder bounded on every side by a monoclinal flexure4 ,furthermore1 since the monoclinal flexure is the structural equivalent of the fault#d1 we may render our conception still simpler by replacing in imagination the encircling flexure by an encircling fault1 and picturing to ourselves the uplifted rock mass as a simple cylinder1 perfectly divided from the surrounding rock and slidden upward so as to project above the surface an amount equal to the depth of the laccolite4 ,footnote #d3 ,exploration of the ,colorado1 pp4 #ahb-ahd4 ,explorations ,west of the #ajjth ,meridian1 ,vol4 ,,iii1 p4 #dh4 ,american ,journal of ,science1 ,july1 #ahgf1 p4 #ba4 ,it is possible to give a mathematical expression to the force necessary to produce such a circular fault4 ,disregarding lithologic differences1 the resistance to the rupture is measured by the area of the faulted surface1 or what is the same thing1 the area of the convex surface of the cylinder4 ,representing the resistance to be overcome by r1 the height of the cylinder 7equal to the depth of the cover of the laccolite7 by d1 and its circumference by c1 we have r dc,c 7#a71 in which ,c is a function of the cohesion of the material and is constant4 ,the force by which the cylinder is lifted and by which it is assumed that the faulting is accomplished1 is communicated through the molten lava of the forming laccolite4 ,being thus communicated it is applied equally to all parts of the base of the cylinder1 and its efficient total is measured by the area of that base4 ,a part of it is devoted to lifting the weight of the cylinder1 and the remainder is devoted to the making of the fault4 ,each of these parts is proportioned1 like the whole1 to the area of the base of the cylinder1 or to the area of the laccolite4 ,representing the portion applied to the faulting by f1 and the area of the laccolite by a1 we have f a ,cl in which ,cl1 is a constant1 and a function of the pressure under which the lava is injected4 ,substituting for a its equivalent1 c f c#b ,cl_/#d and substituting ,cll for the constant term ,cl_/#d f c#b ,cll 7#b7 ,equation #a gives an expression for the resistance which cohesion can oppose to the uplift of the cylinder4 ,equation #b gives an expression for the force exerted by the fluid laccolite toward overcoming the resistance of cohesion4 ,it is evident that for a given value of d it is possible to assign a value of ,c so large that f will be greater than r1 or so small that f will be less than r4 ,that is to say1 at a given depth beneath the surface a laccolite of a certain circumference will be able to force upward the superjacent cylinder of rock1 while a laccolite of a certain smaller circumference will be unable to lift its cover4 ,or in other words1 there is a limit in size beneath which a laccolite cannot be formed4 ,when a lava forced upward through the strata reaches the level at which under the law of hydrostatic equilibrium it must stop1 we may conceive that it expands along some plane of bedding in a thin sheet1 until its horizontal extent becomes so great that it overcomes the resistance offered by the rigidity of its cover1 and it begins to uplift it4 ,the direction of least resistance is now upward1 and the reservoir of lava increases in depth instead of width4 ,the area of a laccolite thus tends to remain at its minimum limit1 and may be regarded as more or less perfectly an index of that limit4 ,in equations #a and #b1 if f r1 then c#b ,cll d c ,c or c d7,c_/,cll7 7#c7 ,that is to say1 if the force exerted by the lava is barely sufficient to overcome the resistance to uplift1 then the circumference of the laccolite is proportional to the depth of its cover4 ,or in other words1 the 7linear7 size of a laccolite is proportioned to its depth beneath the surface4 ,if now we return from the faulted cylinder which for simplicity's sake has been hypothecated1 to the actual cylinder which is surrounded by a flexure instead of a fault1 can we retain our conclusions8 ,with certain modifications ,i think we can4 ,the strains developed in deformation by flexure are less easy of analysis than those which arise in faulting1 but the two cases are in some degree analogous4 ,the expression 7equation #b7 for the force which the lava applies to deformation is unaffected by the manner in which the strata yield4 ,the expression 7equation #a7 for the resistance to deformation by faulting involves two terms1 each in its simplest relations2 the resistance varies directly as the circumference of the laccolite1 and it varies directly as the depth of the cover4 ,in order to pass to an expression for the resistance to deformation by flexure1 only one of these terms need be changed4 ,the resistance bears the same relation to the circumference of the laccolite2 but it is no longer simply proportional to the depth of the cover4 ,it varies more rapidly4 ,if the covering strata were all of a given thickness1 were identical in kind1 and were free to slide upon each other without friction1 their total resistance to deformation would be equal to the resistance of a single stratum multiplied by the number of strata4 ,but since they are not free to slide one upon another1 they sustain each other1 and the resistance offered by the combination is greater than that product4 ,i am led by the analogy of allied problems in mechanics to assume that the resistance of the body of strata varies with some power of its depth1 but ,i am unable to say what power4 ,so far as ,i am aware1 neither mathematical analysis nor experimentation has been directed to the problem in question4 ,according to ,rankine 8the resistances of flexure of similar cross-sections of elastic beams are as their breadths and as the squares of their depths0 78,applied ,mechanics01 page #caf71 and it is possible that the same law applies to the resistances which continuous strata oppose to the uplifts of domes4 ,but it appears more probable that the greater complexity of the strains developed in the formation of domes causes the depth to enter into the formula with a higher power than the second4 ,on the other hand1 some allowance should be made for the fact that the elasticity of the resisting strata is imperfect4 ,if we call the power with which the depth enters the formula a1 equation #a becomes r da c ,clll 7#d74 and equation #c becomes c da 7,clll_/,cll7 7#e74 ,it is probable that the true value of a is not less than #b1 nor more than #c4 ,interpreting these equations in the same manner as those applying to deformation by faulting1 we reach the following conclusions3 #ast4 ,at a given depth beneath the surface1 lava injected under a given pressure cannot form a laccolite of less than a certain area4 ,this may be called its limital area4 #b;d4 ,the pressure of injection remaining constant1 the limital area of a laccolite is a direct function of its depth beneath the surface4 ,the limital area is greater when the depth is greater1 and less when the depth is less4 #c;d4 ,a laccolite of small volume will not exceed the limital area1 but will grow by lifting its cover4 ,if however the volume of intruded lava be great1 its own weight becomes a factor in the equilibrium of forces and modifies the distribution of the pressures4 ,as the rock bubble rises1 the weight of the contained fluid is progressively subtracted from the pressure against its top1 and this proceeds until the upward and lateral pressures become proportional to the resistances which severally oppose them4 ,further expansion is then both upward and outward4 #dth4 ,there is a limit to upward expansion1 dependent on the fact that the pressure due to the combined weight of the laccolite and cover cannot exceed the pressure of the intrusive lava4 ,regarding the intrusive pressure as constant1 it is divisible into three parts1 of which one sustains the weight of the cover1 also constant2 another sustains the weight of the fluid laccolite1 and is measured by its thickness or depth2 and the third produces deformation4 ,when the sum of the weights of the cover and laccolite equals the total pressure of the intrusive lava1 uplift ceases1 and the maximum depth or thickness is attained4 ,we may call this the limital thickness4 ,with regard to simple laccolites the limit is absolute1 but it applies only to the distinct layers of those which are composite2 for a composite laccolite1 built by successive intrusions at wide intervals of time1 may be relieved of part of its load by the erosion of the mound which its expansion causes at the surface of the land4 ,a laccolite formed beneath the bottom of a sea has a greater limital thickness than one formed beneath a land surface2 for the superjacent water being displaced and thrust aside1 is to that extent subtracted from the load to be lifted4 #eth4 ,the laccolite in its formation is constantly solving a problem of 8least force01 and its form is the result4 ,below1 above1 and on all sides its expansion is resisted1 and where the resistance is greatest its contour is least convex4 ,the floor of its chamber is unyielding1 and the bottom of the laccolite is flat4 ,the roof and walls alike yield reluctantly to the pressure1 but the weight of the lava diminishes its pressure on the roof4 ,hence the top of the laccolite becomes broadly convex1 and its edges acutely4 ,local accidents excepted1 the walls oppose an equal resistance on every side2 and the base of the laccolite is rendered circular4 ,the second of the conclusions enunciated above is susceptible of test by observation4 ,by selecting those laccolites of which the dimensions are known with the best degree of approximation1 the following table has been formed3 ,formations4 ,titles of ,laccolites4,diameters,means4 in miles4 ,upper ,zone ,blue ,gate ,shale ,sentinel 4#g 4#ga4b ,tununk ,shale ,geikie 4#ha4b ,a 4#i ,marvine #a4j ,jukes #a4d ,peale #a4h ,flaming ,gorge ,shale,steward #a4ja4d ,b #a4a ,newberry #a4h ,c #a4i ,lower ,zone ,dana #b4j #b4f ,greater ,holmes #b4a ,lesser ,holmes #b4a ,ellsworth #b4c ,pulpit #b4c ,maze #b4h ,crescent #c4f ,hillers #c4i ,there is no laccolite of the upper zone so large as the smallest in the lower zone2 and the mean diameter of those in the lower zone is double the mean of those in the upper4 ,the measurements do not give the diameters of limital areas1 but it is presumable that the actual areas bear substantially the same relation to the limital in the two zones4 ,if we select the smallest laccolites in each group as those most likely to express the limital areas1 the result is practically the same4 ,formations4 ,diameters4 ,means4 ,upper ,zone ,tununk ,shale 4#h 4#i #a4j 4#i #a4j ,flaming ,gorge ,shale #a4ja4je #a4a ,lower ,zone #b4j #b4a #b4a #b4a ,the mean for the lower zone is still double the mean for the upper4 ,the confirmation of the conclusion is as nearly perfect as could have been anticipated4 ,there is no room to doubt that a relation exists between the diameters of laccolites and the depths of their intrusion4 ,having determined by observation the mean size of the laccolites in the upper and lower zones1 as well as the interval which separates the two zones1 and knowing approximately the law which binds the size of the laccolite to its depth of intrusion1 we can compute the depth of intrusion of each zone4 ,our result will doubtless have a large probable error1 but it will not be entirely without value4 ,let x represent the thickness in feet of the original cover of the laccolites of the upper zone2 and x #ccjj the thickness of the cover of the laccolites of the lower zone4 ,the mean circumference in feet of the upper laccolites is #a4b #ebhj #fccf 4 ,the mean circumference of the lower laccolites is #b4f #ebhj #acgbh 4 ,substituting these values in equation #e1 we obtain #fccf xa7,clll_/,cll7 and #acgbh 7x #ccjj7;a7,clll_/,cll7 ,dividing the second equation by the first and reducing1 #ccjj x #ccjj_/7 #a7 7#f74 ,to obtain a minimum result1 assume a #b2 then x #ccjj_/7 #a7 #gjjj feet1 and x #ccjj #ajcjj feet4 ,the summit of the ,masuk sandstone is #c1ejj feet above the mean level of the upper laccolites2 subtracting this from the value of x gives #c1ejj feet as the depth of ,tertiary strata which overlay the ,masuk beds during the epoch of laccolitic intrusion4 ,to obtain a maximum result1 assume a #c2 then x #ccjj_/7 #a7 #aabjj feet1 x #ccjj #adejj feet1 and the result for the depth of the ,tertiary strata is #g1gjj feet4 ,i am far from attaching great weight to this speculation in regard to the original depths of the laccolite covers4 ,it is always hazardous to attempt the quantitative discussion of geological problems1 for the reason that the conditions are apt to be both complex and imperfectly known2 and in this case an uncertainty attaches to the law of relation1 as well as to the quantities to which it is applied4 ,nevertheless after making every allowance there remains a presumption that the cover of the laccolites included some thousands of feet of ,tertiary sediments4 ,what evidence we have then1 indicates that the epoch of laccolitic intrusion was after the accumulation of deep ,tertiary deposits and before the subsequent degradation had made great progress--that it was at or near the close of the epoch of local ,tertiary sedimentation4 ,if the reader would realize the relation between the eroded material and the surviving mountains1 let him turn to the ,frontispiece4 ,a perspective view is there given of a tract ten miles square1 with ,mount ,ellsworth in the center4 ,it is represented as cut out from all surroundings by vertical planes which descend to the level of the ocean4 ,the southern or nearer half of the block shows the present aspect of the country2 the remote half shows the form it is supposed to have had if the uplift was completed before the erosion began1 or what is the same thing1 the form it would have1 had there been no erosion4 ,the difference between the two represents the total amount of the material that has been washed away since the completion of the ,tertiary sediments4 ,partly in review1 let us now sketch the ,,history ,,of ,,the ,,laccolite4 ,when lavas forced upward from lower-lying reservoirs reach the zone in which there is the least hydrostatic resistance to their accumulation1 they cease to rise4 ,if this zone is at the top of the earth's crust they build volcanoes2 if it is beneath1 they build laccolites4 ,light lavas are more apt to produce volcanoes2 heavy1 laccolites4 ,the porphyritic trachytes of the ,plateau ,province produced laccolites4 ,the station of the laccolite being decided1 the first step in its formation is the intrusion along a parting of strata1 of a thin sheet of lava1 which spreads until it has an area adequate1 on the principle of the hydrostatic press1 to the deformation of the covering strata4 ,the spreading sheet always extends itself in the direction of least resistance1 and if the resistances are equal on all sides1 takes a circular form4 ,so soon as the lava can uparch the strata it does so1 and the sheet becomes a laccolite4 ,with the continued addition of lava the laccolite grows in height and width1 until finally the supply of material or the propelling force so far diminishes that the lava clogs by congelation in its conduit and the inflow stops4 ,an irruption is then complete1 and the progress of the laccolite is comparable with that of a volcano at the end of its first eruption4 ,during the irruption and after its completion1 there is an interchange of temperatures4 ,the laccolite cools and solidifies2 its walls are heated and metamorphosed4 ,at the edges1 where the surface of the laccolite is most convex1 the heat is most rapidly dissipated1 and its effect in metamorphism is least4 ,a second irruption may take place either before or after the first is solidified4 ,it may intrude above or it may intrude beneath it2 and observation has not yet distinguished the one case from the other4 ,in any case it carries forward the deformation of cover that was begun by the first1 and combines with it in such way that the compound form is symmetric1 and is substantially the same that would have been produced if the two irruptions were combined in one4 ,thus the laccolite grows by successive accretions until at length its cooled mass1 heavier and stronger than the surrounding rocks1 proves a sufficient obstacle to intrusion4 ,the next irruption then avoids it1 opens a new conduit1 and builds a new laccolite at its side4 ,by successive shiftings of the conduit a group of laccolites is formed1 just as by the shifting of vents eruptive cones are grouped4 ,each laccolite is a subterranean volcano4 ,illustration3 ,,fig4 #ec4--;,diagram to illustrate the relation of ,dikes and ,sheets to the ,strains which are developed in the uplifting of laccolitic arches4 ,the strata above the laccolite are bent instead of broken1 because their material is subjected to so great a pressure by superincumbent strata that it cannot hold an open fissure and is quasi-plastic4 ,but although quasi-plastic it is none the less solid1 and can be cracked open if the gap is instantaneously filled1 the cracking and the filling being one event4 ,this happens in the immediate walls of the laccolite1 and they are injected by dikes and sheets of the lava4 ,the directions of the cracks are normal to the directions of the extensive strains 7strains tending to extend7 where they occur4 ,from the top of the laccolite dikes run upward into the roof1 marking horizontal strains 7a a74 ,from the sides smaller vertical dikes run outward1 marking horizontal1 tangential strains4 ,and parallel to the sides near the base of the laccolite1 are numerous sheets1 marking strains directed outward and upward 7c c74 ,these last especially serve to show that the rigidity of the strata is not abolished1 although it is overpowered1 by the pressure which warps them4 ,here we are brought face to face with a great fact of dynamic geology which though well known is too often ignored4 ,the solid crust of the earth1 and the solid earth if it be solid1 are as plastic in great masses as wax is in small4 ,solidity is not absolute but relative4 ,it is only a low grade of plasticity4 ,the rigidity or strength of a body is measured by the square of its linear dimensions1 while its weight is measured by the cube4 ,hence with increase in magnitude1 the weight increases more rapidly than the strength2 and no very large body is strong enough to withstand the pressure of its own weight4 ,however solid it may be1 it must succumb and be flattened4 ,when we speak of rock masses which are measured by feet1 we may regard them as solid2 but when we consider masses which are measured by miles1 we should regard them as plastic4 ,the same principle is illustrated by the limital area of laccolites4 ,a small laccolite cannot lift its small cover1 but a large laccolite can lift its correspondingly large cover4 ,the strength or rigidity which resists deformation is overcome by magnitude4 ,laccolites of ,other ,regions4--,in many lands geologists have observed intrusive rocks occurring in great bodies1 but ,i am not aware that such a system as that of the ,henry ,mountains has ever been described4 ,doubtless all such bodies are laccolitic1 but the combination of conditions which this field presents can rarely be repeated4 ,in the first place the strata which here contain the laccolites lay level4 ,they had suffered no displacement before the epoch of irruption1 and they have suffered none since4 ,the laccolitic phenomena stand by themselves1 with nothing to mar their symmetry or complicate their study4 ,in the next place the laccolites are here assembled in such number and with such variety of size1 form1 and horizon that there is little danger of mistaking accidental features for essential4 ,again1 the region having been recently elevated is the scene of rapid degradation4 ,waterways are deeply corraded1 slopes are steep1 and escarpments abound4 ,and finally the climate is so arid that vegetation is exceedingly scant4 ,the rocks are for the most part bare and their examination is unobstructed4 ,if the conditions of erosion and climate had been unfavorable in the ,henry ,mountains1 they could not have yielded the key to the laccolitic structure2 but the key once found1 it is to be anticipated that the structure will be recognized in other laccolites of which the exposures are less perfect4 ,if the strata had experienced anterior displacements so as to be inclined1 folded1 and faulted1 a symmetrical growth of laccolites would have been impossible1 and the mountains would not have yielded a knowledge of the type form4 ,but the type form being known1 it is to be anticipated that in disturbed regions aberrant forms will be recognized and referred to the type4 ,possible ,analogues of the ,laccolite4--,all the arches of the ,henry ,mountains have been ascribed to laccolites1 whether their nuclei were visible or concealed1 and the evidence upon which the latter were included appears to admit of no controversy4 ,the question arises whether the great flexures of the ,plateau region may not be allied in structure4 ,the volcano having its homologue in the laccolite1 may not broad lava fields have their homologues beneath displacements of the ,kaibab type8 ,the idea is naturally attractive to one who has made a special study of laccolites1 but it is hardly tenable4 ,there are indeed many points of resemblance between such flexures as the ,waterpocket1 and the uplifts of the ,henry ,mountains2 but the points of contrast are equally conspicuous1 and seem to mark a radical difference4 ,there is a certain symmetry of form which is characteristic of the laccolitic arches1 but which is rarely seen in the great flexures4 ,and there is a linear element which is characteristic of the latter1 but not of the former4 ,the great flexures always have direction or trend1 and often exhibit parallelism2 the laccolitic arches betray no trend either individually or collectively4 ,these features are well shown in ,plate ,,ii1 where the ,waterpocket flexure is contrasted with the ,henry ,mountain arches4 ,,chapter ,v4 ,,land ,,sculpture4 ,the ,basin of the ,colorado offers peculiar facilities for the study of the origin of topographic forms1 and its marvelous sculpture has excited the interest of every observer4 ,it has already made notable contributions to the principles of earth sculpture#e1 and its resources are far from exhausted4 ,the study of the ,henry ,mountains has not proved entirely unfruitful1 and for the sake of showing the bearing of its peculiar features upon the general subject1 ,i shall take the liberty to restate certain principles of erosion which have been derived or enforced by the study of the ,colorado ,plateaus4 ,footnote #e3 ,geology of the 8,colorado ,exploring ,expedition01 by ,j4 ,s4 ,newberry1 p4 #de4 8,exploration of the ,colorado ,river of the ,west01 by ,j4 ,w4 ,powell1 p4 #aeb4 8,geology of the ,uinta ,mountains01 by ,j4 ,w4 ,powell1 p4 #aha4 8,explorations ,west of the #ajjth ,meridian01 ,vol4 ,,iii1 ,part ,i1 by ,g4 ,k4 ,gilbert1 pp4 #fg and #eed4 8,the ,colorado ,plateau ,region0 in ,american ,journal of ,science for ,august1 #ahgf1 by ,g4 ,k4 ,gilbert4 ,a portion of the last paper is repeated1 after modification1 in the first section of this chapter4 ,i4--,,erosion4 ,the sculpture and degradation of the land are performed partly by shore waves1 partly by glaciers1 partly by wind2 but chiefly by rain and running water4 ,the last mentioned agencies only will be here discussed4 ,the erosion which they accomplish will be considered 7,a7 as consisting of parts1 and 7,b7 as modified by conditions4 ,a4 ,,processes ,,of ,,erosion4 ,all indurated rocks and most earths are bound together by a force of cohesion which must be overcome before they can be divided and removed4 ,the natural processes by which the division and removal are accomplished make up erosion4 ,they are called disintegration and transportation4 ,transportation is chiefly performed by running water4 ,disintegration is naturally divided into two parts4 ,so much of it as is accomplished by running water is called corrasion1 and that which is not1 is called weathering4 ,stated in their natural order1 the three general divisions of the process of erosion are 7#a7 weathering1 7#b7 transportation1 and 7#c7 corrasion4 ,the rocks of the general surface of the land are disintegrated by weathering4 ,the material thus loosened is transported by streams to the ocean or other receptacle4 ,in transit it helps to corrade from the channels of the streams other material1 which joins with it to be transported to the same goal4 ,weathering4 ,in weathering the chief agents of disintegration are solution1 change of temperature1 the beating of rain1 gravity1 and vegetation4 ,the great solvent of rocks is water1 but it receives aid from some other substances of which it becomes the vehicle4 ,these substances are chiefly products of the formation and decomposition of vegetable tissues4 ,some rocks are disintegrated by their complete solution1 but the great majority are divided into grains by the solution of a portion2 and fragmental rocks usually lose by solution the cement merely1 and are thus reduced to their original incoherent condition4 ,the most rigid rocks are cracked by sudden changes of temperature2 and the crevices thus begun are opened by the freezing of the water within them4 ,the coherence of the more porous rocks is impaired and often destroyed by the same expansive force of freezing water4 ,the beating of the rain overcomes the feeble coherence of earths1 and assists solution and frost by detaching the particles which they have partially loosened4 ,when the base of a cliff is eroded so as to remove or diminish the support of the upper part1 the rock thus deprived of support is broken off in blocks by gravity4 ,the process of which this is a part is called cliff erosion or sapping4 ,plants often pry apart rocks by the growth of their roots1 but their chief aid to erosion is by increasing the solvent power of percolating water4 ,in general soft rocks weather more rapidly than hard4 ,transportation4 ,a portion of the water of rains flows over the surface and is quickly gathered into streams4 ,a second portion is absorbed by the earth or rock on which it falls1 and after a slow underground circulation reissues in springs4 ,both transport the products of weathering1 the latter carrying dissolved minerals and the former chiefly undissolved4 ,transportation is also performed by the direct action of gravity4 ,in sapping1 the blocks which are detached by gravity are by the same agency carried to the base of the cliff4 ,corrasion4 ,in corrasion the agents of disintegration are solution and mechanical wear4 ,wherever the two are combined1 the superior efficiency of the latter is evident2 and in all fields of rapid corrasion the part played by solution is so small that it may be disregarded4 ,the mechanical wear of streams is performed by the aid of hard mineral fragments which are carried along by the current4 ,the effective force is that of the current2 the tools are mud1 sand1 and bowlders4 ,the most important of them is sand2 it is chiefly by the impact and friction of grains of sand that the rocky beds of streams are disintegrated4 ,streams of clear water corrade their beds by solution4 ,muddy streams act partly by solution1 but chiefly by attrition4 ,streams transport the combined products of corrasion and weathering4 ,a part of the dbris is carried in solution1 and a part mechanically4 ,the finest of the undissolved detritus is held in suspension2 the coarsest is rolled along the bottom2 and there is a gradation between the two modes4 ,there is a constant comminution of all the material as it moves1 and the work of transportation is thereby accelerated4 ,bowlders and pebbles1 while they wear the stream bed by pounding and rubbing1 are worn still more rapidly themselves4 ,sand grains are worn and broken by the continued jostling1 and their fragments join the suspended mud4 ,finally the detritus is all more or less dissolved by the water1 the finest the most rapidly4 ,in brief1 weathering is performed by solution2 by change of temperature1 including frost2 by rain beating2 by gravity2 and by vegetation4 ,transportation is performed chiefly by running water4 ,corrasion is performed by solution1 and by mechanical wear4 ,corrasion is distinguished from weathering chiefly by including mechanical wear among its agencies1 and the importance of the distinction will be apparent when we come to consider how greatly and peculiarly this process is affected by modifying conditions4 ,b4 ,,conditions ,,controlling ,,erosion4 ,the chief conditions which affect the rapidity of erosion are 7#a7 declivity1 7#b7 character of rock1 and 7#c7 climate4 ,rate of ,erosion and ,declivity4 ,in general erosion is most rapid where the slope is steepest2 but weathering1 transportation1 and corrasion are affected in different ways and in different degrees4 ,with increase of slope goes increase in the velocity of running water1 and with that goes increase in its power to transport undissolved detritus4 ,the ability of a stream to corrade by solution is not notably enhanced by great velocity2 but its ability to corrade by mechanical wear keeps pace with its ability to transport1 or may even increase more rapidly4 ,for not only does the bottom receive more blows in proportion as the quantity of transient detritus increases1 but the blows acquire greater force from the accelerated current1 and from the greater size of the moving fragments4 ,it is necessary however to distinguish the ability to corrade from the rate of corrasion1 which will be seen further on to depend largely on other conditions4 ,weathering is not directly influenced by slope1 but it is reached indirectly through transportation4 ,solution and frost1 the chief agents of rock decay1 are both retarded by the excessive accumulation of disintegrated rock4 ,frost action ceases altogether at a few feet below the surface1 and solution gradually decreases as the zone of its activity descends and the circulation on which it depends becomes more sluggish4 ,hence the rapid removal of the products of weathering stimulates its action1 and especially that portion of its action which depends upon frost4 ,if however the power of transportation is so great as to remove completely the products of weathering1 the work of disintegration is thereby checked2 for the soil which weathering tends to accumulate is a reservoir to catch rain as it reaches the earth and store it up for the work of solution and frost1 instead of letting it run off at once unused4 ,sapping is directly favored by great declivity4 ,in brief1 a steep declivity favors transportation and thereby favors corrasion4 ,the rapid1 but partial1 transportation of weathered rock accelerates weathering2 but the complete removal of its products retards weathering4 ,rate of ,erosion and ,rock ,texture4 ,other things being equal1 erosion is most rapid when the eroded rock offers least resistance2 but the rocks which are most favorable to one portion of the process of erosion do not necessarily stand in the same relation to the others4 ,disintegration by solution depends in large part on the solubility of the rocks1 but it proceeds most rapidly with those fragmental rocks of which the cement is soluble1 and of which the texture is open4 ,disintegration by frost is most rapid in rocks which absorb a large percentage of water and are feebly coherent4 ,disintegration by mechanical wear is most rapid in soft rocks4 ,transportation is most favored by those rocks which yield by disintegration the most finely comminuted dbris4 ,rate of ,erosion and ,climate4 ,the influence of climate upon erosion is less easy to formulate4 ,the direct influences of temperature and rainfall are comparatively simple1 but their indirect influence through vegetation is complex1 and is in part opposed to the direct4 ,temperature affects erosion chiefly by its changes4 ,where the range of temperature includes the freezing point of water1 frost contributes its powerful aid to weathering2 and it is only where changes are great and sudden that rocks are cracked by their unequal expansion or contraction4 ,all the processes of erosion are affected directly by the amount of rainfall1 and by its distribution through the year4 ,all are accelerated by its increase and retarded by its diminution4 ,when it is concentrated in one part of the year at the expense of the remainder1 transportation and corrasion are accelerated1 and weathering is retarded4 ,weathering is favored by abundance of moisture4 ,frost accomplishes most when the rocks are saturated2 and solution when there is the freest subterranean circulation4 ,but when the annual rainfall is concentrated into a limited season1 a larger share of the water fails to penetrate1 and the gain from temporary flooding does not compensate for the checking of all solution by a long dry season4 ,transportation is favored by increasing water supply as greatly as by increasing declivity4 ,when the volume of a stream increases1 it becomes at the same time more rapid1 and its transporting capacity gains by the increment to velocity as well as by the increment to volume4 ,hence the increase in power of transportation is more than proportional to the increase of volume4 ,it is due to this fact chiefly that the transportation of a stream which is subject to floods is greater than it would be if its total water supply were evenly distributed in time4 ,the indirect influence of rainfall and temperature1 by means of vegetation1 has different laws4 ,vegetation is intimately related to water supply4 ,there is little or none where the annual precipitation is small1 and it is profuse where the latter is great--especially where the temperature is at the same time high4 ,in proportion as vegetation is profuse the solvent power of percolating water is increased1 and on the other hand the ground is sheltered from the mechanical action of rains and rills4 ,the removal of disintegrated rock is greatly impeded by the conservative power of roots and fallen leaves1 and a soil is thus preserved4 ,transportation is retarded4 ,weathering by solution is accelerated up to a certain point1 but in the end it suffers by the clogging of transportation4 ,the work of frost is nearly stopped as soon as the depth of soil exceeds the limit of frost action4 ,the force of rain drops is expended on foliage4 ,moreover a deep soil acts as a distributing reservoir for the water of rains1 and tends to equalize the flow of streams4 ,hence the general effect of vegetation is to retard erosion2 and since the direct effect of great rainfall is the acceleration of erosion1 it results that its direct and indirect tendencies are in opposite directions4 ,in arid regions of which the declivities are sufficient to give thorough drainage1 the absence of vegetation is accompanied by absence of soil4 ,when a shower falls1 nearly all the water runs off from the bare rock1 and the little that is absorbed is rapidly reduced by evaporation4 ,solution becomes a slow process for lack of a continuous supply of water1 and frost accomplishes its work only when it closely follows the infrequent rain4 ,thus weathering is retarded4 ,transportation has its work so concentrated by the quick gathering of showers into floods1 as to compensate1 in part at least1 for the smallness of the total rainfall from which they derive their power4 ,hence in regions of small rainfall1 surface degradation is usually limited by the slow rate of disintegration2 while in regions of great rainfall it is limited by the rate of transportation4 ,there is probably an intermediate condition with moderate rainfall1 in which a rate of disintegration greater than that of an arid climate is balanced by a more rapid transportation than consists with a very moist climate1 and in which the rate of degradation attains its maximum4 ,over nearly the whole of the earth's surface there is a soil1 and wherever this exists we know that the conditions are more favorable to weathering than to transportation4 ,hence it is true in general that the conditions which limit transportation are those which limit the general degradation of the surface4 ,to understand the manner in which this limit is reached it is necessary to look at the process by which the work is accomplished4 ,transportation and ,comminution4 ,a stream of water flowing down its bed expends an amount of energy that is measured by the quantity of water and the vertical distance through which it descends4 ,if there were no friction of the water upon its channel the velocity of the current would continually increase2 but if1 as is the usual case1 there is no increase of velocity1 then the whole of the energy is consumed in friction4 ,the friction produces inequalities in the motion of the water1 and especially induces subsidiary currents more or less oblique to the general onward movement4 ,some of these subsidiary currents have an upward tendency1 and by them is performed the chief work of transportation4 ,they lift small particles from the bottom and hold them in suspension while they move forward with the general current4 ,the finest particles sink most slowly and are carried farthest before they fall4 ,larger ones are barely lifted1 and are dropped at once4 ,still larger are only half lifted2 that is1 they are lifted on the side of the current and rolled over without quitting the bottom4 ,and finally there is a limit to the power of every current1 and the largest fragments of its bed are not moved at all4 ,there is a definite relation between the velocity of a current and the size of the largest bowlder it will roll4 ,it has been shown by ,hopkins that the weight of the bowlder is proportioned to the sixth power of the velocity4 ,it is easily shown also that the weight of a suspended particle is proportioned to the sixth power of the velocity of the upward current that will prevent its sinking4 ,but it must not be inferred that the total load of detritus that a stream will transport bears any such relation to the rapidity of its current4 ,the true inference is1 that the velocity determines the size-limit of the detritus that a stream can move by rolling1 or can hold in suspension4 ,every particle which a stream lifts and sustains is a draft upon its energy1 and the measure of the draft is the weight 7weighed in water7 of the particle1 multiplied by the distance it would sink in still water in the time during which it is suspended4 ,if for the sake of simplicity we suppose the whole load of a stream to be of uniform particles1 then the measure of the energy consumed in their transportation is their total weight multiplied by the distance one of them would sink in the time occupied in their transportation4 ,since fine particles sink more slowly than coarse1 the same consumption of energy will convey a greater load of fine than of coarse4 ,again1 the energy of a clear stream is entirely consumed in the friction of flow2 and the friction bears a direct relation to its velocity4 ,but if detritus be added to the water1 then a portion of its energy is diverted to the transportation of the load2 and this is done at the expense of the friction of flow1 and hence at the expense of velocity4 ,as the energy expended in transportation increases1 the velocity diminishes4 ,if the detritus be composed of uniform particles1 then we may also say that as the load increases the velocity diminishes4 ,but the diminishing velocity will finally reach a point at which it can barely transport particles of the given size1 and when this point is attained1 the stream has its maximum load of detritus of the given size4 ,but fine detritus requires less velocity for its transportation than coarse1 and will not so soon reduce the current to the limit of its efficiency4 ,a greater percentage of the total energy of the stream can hence be employed by fine detritus than by coarse4 7,it should be explained that the friction of flow is in itself a complex affair4 ,the water in contact with the bottom and walls of the channel develops friction by flowing past them1 and that which is farther away by flowing past that which is near4 ,the inequality of motion gives rise to cross currents and there is a friction of these upon each other4 ,the ratio or coefficient of friction of water against the substance of the bed1 the coefficient of friction of water against water1 or the viscosity of water1 and the form of the bed1 all conspire to determine the resistance of flow and together make up what may be called the coefficient of the friction of flow4 ,the friction depends on its coefficient and on the velocity47 ,thus the capacity of a stream for transportation is enhanced by comminution in two ways4 ,fine detritus1 on the one hand1 consumes less energy for the transportation of the same weight1 and on the other1 it can utilize a greater portion of the stream's energy4 ,it follows1 as a corollary1 that the velocity of a fully loaded stream depends 7ceteris paribus7 on the comminution of the material of the load4 ,when a stream has its maximum load of fine detritus1 its velocity will be less than when carrying its maximum load of coarse detritus2 and the greater load corresponds to the less velocity4 ,it follows also that a stream which is supplied with heterogeneous dbris will select the finest4 ,if the finest is sufficient in quantity the current will be so checked by it that the coarser cannot be moved4 ,if the finest is not sufficient the next grade will be taken1 and so on4 ,transportation and ,declivity4 ,to consider now the relation of declivity to transportation we will assume all other conditions to be constant4 ,let us suppose that two streams have the same length1 the same quantity of water1 flow over beds of the same character1 and are supplied to their full capacities with detritus of the same kind2 but differ in the total amount of fall4 ,their declivities or rates of fall are proportional to their falls4 ,since the energy of a stream is measured by the product of its volume and its fall1 the relative energies of the two streams are proportional to their falls1 and hence proportional to their declivities4 ,the velocities of the two streams1 depending1 as we have seen above1 on the character of the detritus which loads them1 are the same2 and hence the same amount of energy is consumed by each in the friction of flow4 ,and since the energy which each stream expends in transportation is the residual after deducting what it spends in friction from its total energy1 it is evident that the stream with the greater declivity will not merely have the greater energy1 but will expend a less percentage of it in friction and a greater percentage in transportation4 ,hence declivity favors transportation in a degree that is greater than its simple ratio4 ,there are two elements of which no account is taken in the preceding discussion1 but which need to be mentioned to prevent misapprehension1 although they detract in no way from the conclusions4 ,the first is the addition which the transported detritus makes to the energy of the stream4 ,a stream of water charged with detritus is at once a compound and an unstable fluid4 ,it has been treated merely as an unstable fluid requiring a constant expenditure of energy to maintain its constitution2 but looking at it as a compound fluid1 it is plain that the energy it develops by its descent is greater than the energy pertaining to the water alone1 in the precise ratio of the mass of the mixture to the mass of the simple water4 ,the second element is the addition which the detritus makes to the friction of flow4 ,the coefficient of friction of the compound stream upon its bottom will always be greater than that of the simple stream of water1 and the coefficient of internal friction or the viscosity will be greater than that of pure water1 and hence for the same velocity a greater amount of energy will be consumed4 ,it may be noted in passing1 that the energy which is consumed in the friction of the detritus on the stream bed1 accomplishes as part of its work the mechanical corrasion of the bed4 ,transportation and ,quantity of ,water4 ,a stream's friction of flow depends mainly on the character of the bed1 on the area of the surface of contact1 and on the velocity of the current4 ,when the other elements are constant1 the friction varies approximately with the area of contact4 ,the area of contact depends on the length and form of the channel1 and on the quantity of water4 ,for streams of the same length and same form of cross-section1 but differing in size of cross-section1 the area of contact varies directly as the square root of the quantity of water4 ,hence1 ceteris paribus1 the friction of a stream on its bed is proportioned to the square root of the quantity of water4 ,but as stated above1 the total energy of a stream is proportioned directly to the quantity of water2 and the total energy is equal to the energy spent in friction1 plus the energy spent in transportation4 ,whence it follows that if a stream change its quantity of water without changing its velocity or other accidents1 the total energy will change at the same rate as the quantity of water2 the energy spent in friction will change at a less rate1 and the energy remaining for transportation will change at a greater rate4 ,hence increase in quantity of water favors transportation in a degree that is greater than its simple ratio4 ,it follows as a corollary that the running water which carries the dbris of a district loses power by subdivision toward its sources2 and that1 unless there is a compensating increment of declivity1 the tributaries of a river will fail to supply it with the full load it is able to carry4 ,it is noteworthy also that the obstruction which vegetation opposes to transportation is especially effective in that it is applied at the infinitesimal sources of streams1 where the force of the running water is least4 ,a stream which can transport dbris of a given size1 may be said to be competent to such dbris4 ,since the maximum particles which streams are able to move are proportioned to the sixth powers of their velocities1 competence depends on velocity4 ,velocity1 in turn1 depends on declivity and volume1 and 7inversely7 on load4 ,in brief1 the capacity of a stream for transportation is greater for fine dbris than for coarse4 ,its capacity for the transportation of a given kind of dbris is enlarged in more than simple ratio by increase of declivity2 and it is enlarged in more than simple ratio by increase of volume4 ,the competence of a stream for the transport of dbris of a given fineness1 is limited by a corresponding velocity4 ,the rate of transportation of dbris of a given fineness may equal the capacity of the transporting stream1 or it may be less4 ,when it is less1 it is always from the insufficiency of supply4 ,the supply furnished by weathering is never available unless the degree of fineness of the dbris brings it within the competence of the stream at the point of supply4 ,the chief point of supply is at the very head of the flowing water4 ,the rain which falls on material that has been disintegrated by weathering1 begins after it has saturated the immediate surface to flow off4 ,but it forms a very thin sheet2 its friction is great2 its velocity is small2 and it is competent to pick up only particles of exceeding fineness4 ,if the material is heterogeneous1 it discriminates and leaves the coarser particles4 ,as the sheet moves on it becomes deeper and soon begins to gather itself into rills4 ,as the deepening and concentration of water progresses1 either its capacity increases and the load of fine particles is augmented1 or1 if fine particles are not in sufficient force1 its competence increases1 and larger ones are lifted4 ,in either case the load is augmented1 and as rill joins rill it steadily grows1 until the accumulated water finally passes beyond the zone of disintegrated material4 ,the particles which the feeble initial currents are not competent to move1 have to wait either until they are subdivided by the agencies of weathering1 or until the deepening of the channels of the rills so far increases the declivities that the currents acquire the requisite velocity1 or until some fiercer storm floods the ground with a deeper sheet of water4 ,thus rate of transportation1 as well as capacity for transportation1 is favored by fineness of dbris1 by declivity1 and by quantity of water4 ,it is opposed chiefly by vegetation1 which holds together that which is loosened by weathering1 and shields it from the agent of transportation in the very place where that agent is weakest4 ,when the current of a stream gradually diminishes in its course--as for example in approaching the ocean--the capacity for transportation also diminishes2 and so soon as the capacity becomes less than the load1 precipitation begins--the coarser particles being deposited first4 ,corrasion and ,transportation4 ,where a stream has all the load of a given degree of comminution which it is capable of carrying1 the entire energy of the descending water and load is consumed in the translation of the water and load and there is none applied to corrasion4 ,if it has an excess of load its velocity is thereby diminished so as to lessen its competence and a portion is dropped4 ,if it has less than a full load it is in condition to receive more and it corrades its bottom4 ,a fully loaded stream is on the verge between corrasion and deposition4 ,as will be explained in another place1 it may wear the walls of its channel1 but its wear of one wall will be accompanied by an addition to the opposite wall4 ,the work of transportation may thus monopolize a stream to the exclusion of corrasion1 or the two works may be carried forward at the same time4 ,corrasion and ,declivity4 ,the rapidity of mechanical corrasion depends on the hardness1 size1 and number of the transient fragments1 on the hardness of the rock-bed1 and on the velocity of the stream4 ,the blows which the moving fragments deal upon the stream bed are hard in proportion as the fragments are large and the current is swift4 ,they are most effective when the fragments are hard and the bed-rock is soft4 ,they are more numerous and harder upon the bottom of the channel than upon the sides because of the constant tendency of the particles to sink in water4 ,their number is increased up to a certain limit by the increase of the load of the stream2 but when the fragments become greatly crowded at the bottom of a stream their force is partially spent among themselves1 and the bed-rock is in the same degree protected4 ,for this reason1 and because increase of load causes retardation of current1 it is probable that the maximum work of corrasion is performed when the load is far within the transporting capacity4 ,the element of velocity is of double importance since it determines not only the speed1 but to a great extent the size of the pestles which grind the rocks4 ,the coefficients upon which it in turn depends1 namely1 declivity and quantity of water1 have the same importance in corrasion that they have in transportation4 ,let us suppose that a stream endowed with a constant volume of water1 is at some point continuously supplied with as great a load as it is capable of carrying4 ,for so great a distance as its velocity remains the same1 it will neither corrade 7downward7 nor deposit1 but will leave the grade of its bed unchanged4 ,but if in its progress it reaches a place where a less declivity of bed gives a diminished velocity1 its capacity for transportation will become less than the load and part of the load will be deposited4 ,or if in its progress it reaches a place where a greater declivity of bed gives an increased velocity1 the capacity for transportation will become greater than the load and there will be corrasion of the bed4 ,in this way a stream which has a supply of dbris equal to its capacity1 tends to build up the gentler slopes of its bed and cut away the steeper4 ,it tends to establish a single1 uniform grade4 ,let us now suppose that the stream after having obliterated all the inequalities of the grade of its bed loses nearly the whole of its load4 ,its velocity is at once accelerated and vertical corrasion begins through its whole length4 ,since the stream has the same declivity and consequently the same velocity at all points1 its capacity for corrasion is everywhere the same4 ,its rate of corrasion however will depend on the character of its bed4 ,where the rock is hard corrasion will be less rapid than where it is soft1 and there will result inequalities of grade4 ,but so soon as there is inequality of grade there is inequality of velocity1 and inequality of capacity for corrasion2 and where hard rocks have produced declivities1 there the capacity for corrasion will be increased4 ,the differentiation will proceed until the capacity for corrasion is everywhere proportioned to the resistance1 and no further1--that is1 until there is an equilibrium of action4 ,in general1 we may say that a stream tends to equalize its work in all parts of its course4 ,its power inheres in its fall1 and each foot of fall has the same power4 ,when its work is to corrade and the resistance is unequal1 it concentrates its energy where the resistance is great by crowding many feet of descent into a small space1 and diffuses it where the resistance is small by using but a small fall in a long distance4 ,when its work is to transport1 the resistance is constant and the fall is evenly distributed by a uniform grade4 ,when its work includes both transportation and corrasion1 as in the usual case1 its grades are somewhat unequal2 and the inequality is greatest when the load is least4 ,it is to be remarked that in the case of most streams it is the flood stage which determines the grades of the channel4 ,the load of detritus is usually greatest during the highest floods1 and power is conferred so rapidly with increase of quantity of water1 that in any event the influence of the stream during its high stage will overpower any influence which may have been exerted at a low stage4 ,that relation of transportation to corrasion which subsists when the water is high will determine the grades of the waterway4 ,declivity and ,quantity of ,water4 ,the conclusions reached in regard to the relations of corrasion and declivity depend on the assumption that the volume of the stream is the same throughout its whole course1 and they consequently apply directly to such portions only of streams as are not increased by tributaries4 ,a simple modification will include the more general case of branching streams4 ,let us suppose that two equal streams which join1 have the same declivity1 and are both fully loaded with detritus of the same kind4 ,if the channel down which they flow after union has also the same declivity1 then the joint stream will have a greater velocity than its branches1 its capacity for transportation will be more than adequate for the joint load1 and it will corrade its bottom4 ,by its corrasion it will diminish the declivity of its bed1 and consequently its velocity and capacity for transportation1 until its capacity is equal to the total capacity of its tributaries4 ,when an equilibrium of action is reached1 the declivity of the main stream will be less than the declivities of its branches4 ,this result does not depend on the assumed equality of the branches1 nor upon their number4 ,it is equally true that in any river system which is fully supplied with material for transportation and which has attained a condition of equal action1 the declivity of the smaller streams is greater than that of the larger4 ,let us further suppose that two equal streams which join1 are only partially loaded1 and are corrading at a common rate a common rock4 ,if the channel down which they flow after union is in the same rock and has the same declivity1 then the joint river will have a greater velocity1 and will corrade more rapidly than its branches4 ,by its more rapid corrasion it will diminish the declivity of its bed1 until as before there is an equilibrium of action1--the branch having a greater declivity than the main4 ,this result also is independent of the number and equality of the branches2 and it is equally true that in any river system which traverses and corrades rock of equal resistance throughout1 and which has reached a condition of equal action1 the declivity of the smaller streams is greater than that of the larger4 ,in general we may say that1 ceteris paribus1 declivity hears an inverse relation to quantity of water4 7,there is an apparent exception to this law1 which is specially noteworthy in the sculpture of bad-lands1 and will be described in another place74 ,,ii4 ,,sculpture4 ,erosion may be regarded from several points of view4 ,it lays bare rocks which were before covered and concealed1 and is thence called denudation4 ,it reduces the surfaces of mountains1 plateaus1 and continents1 and is thence called degradation4 ,it carves new forms of land from those which before existed1 and is thence called land sculpture4 ,in the following pages it will be considered as land sculpture1 and attention will be called to certain principles of erosion which are concerned in the production of topographic forms4 ,sculpture and ,declivity4 ,we have already seen that erosion is favored by declivity4 ,where the declivity is great the agents of erosion are powerful2 where it is small they are weak2 where there is no declivity they are powerless4 ,moreover it has been shown that their power increases with the declivity in more than simple ratio4 ,it is evident that if steep slopes are worn more rapidly than gentle1 the tendency is to abolish all differences of slope and produce uniformity4 ,the law of uniform slope thus opposes diversity of topography1 and if not complemented by other laws1 would reduce all drainage basins to plains4 ,but in reality it is never free to work out its full results2 for it demands a uniformity of conditions which nowhere exists4 ,only a water sheet of uniform depth1 flowing over a surface of homogeneous material1 would suffice2 and every inequality of water depth or of rock texture produces a corresponding inequality of slope and diversity of form4 ,the reliefs of the landscape exemplify other laws1 and the law of uniform slopes is merely the conservative element which limits their results4 ,sculpture and ,structure2 the ,law of ,structure4 ,we have already seen that erosion is influenced by rock character4 ,certain rocks1 of which the hard are most conspicuous1 oppose a stubborn resistance to erosive agencies2 certain others1 of which the soft are most conspicuous1 oppose a feeble resistance4 ,erosion is most rapid where the resistance is least1 and hence as the soft rocks are worn away the hard are left prominent4 ,the differentiation continues until an equilibrium is reached through the law of declivities4 ,when the ratio of erosive action as dependent on declivities becomes equal to the ratio of resistances as dependent on rock character1 there is equality of action4 ,in the structure of the earth's crust hard and soft rocks are grouped with infinite diversity of arrangement4 ,they are in masses of all forms1 and dimensions1 and positions2 and from these forms are carved an infinite variety of topographic reliefs4 ,in so far as the law of structure controls sculpture1 hard masses stand as eminences and soft are carved in valleys4 ,the ,law of ,divides4 ,we have seen that the declivity over which water flows bears an inverse relation to the quantity of water4 ,if we follow a stream from its mouth upward and pass successively the mouths of its tributaries1 we find its volume gradually less and less and its grade steeper and steeper1 until finally at its head we reach the steepest grade of all4 ,if we draw the profile of the river on paper1 we produce a curve concave upward and with the greatest curvature at the upper end4 ,the same law applies to every tributary and even to the slopes over which the freshly fallen rain flows in a sheet before it is gathered into rills4 ,the nearer the watershed or divide the steeper the slope2 the farther away the less the slope4 ,it is in accordance with this law that mountains are steepest at their crests4 ,the profile of a mountain if taken along drainage lines is concave outward as represented in the diagram2 and this is purely a matter of sculpture1 the uplifts from which mountains are carved rarely if ever assuming this form4 ,illustration3 ,,fig4 #ed4--,typical profile of the ,drainage ,slopes of ,mountains4 ,under the law of ,structure and the law of ,divides combined1 the features of the earth are carved4 ,declivities are steep in proportion as their material is hard2 and they are steep in proportion as they are near divides4 ,the distribution of hard and soft rocks1 or the geological structure1 and the distribution of drainage lines and watersheds1 are coefficient conditions on which depends the sculpture of the land4 ,in the sequel it will be shown that the distribution of drainage lines and watersheds depends in part on that of hard and soft rocks4 ,in some places the first of the two conditions is the more important1 in others the second4 ,in the bed of a stream without tributaries the grade depends on the structure of the underlying rocks4 ,in rock which is homogeneous and structureless all slopes depend on the distribution of divides and drainage lines4 ,the relative importance of the two conditions is especially affected by climate1 and the influence of this factor is so great that it may claim rank as a third condition of sculpture4 ,sculpture and ,climate4 ,the ,henry ,mountains consist topographically of five individuals1 separated by low passes1 and practically independent in climate4 ,at the same time they are all of one type of structure1 being constituted by similar aggregation of hard and soft rocks4 ,their altitudes appear in the following table4 ,altitude above the sea4 ,mount ,ellen #aa1bej feet4 ,mount ,pennell #aa1aej feet4 ,mount ,hillers #aj1ejj feet4 ,mount ,ellsworth #h1jjj feet4 ,mount ,holmes #g1gge feet4 ,the plain on which they stand has a mean altitude of #e1ejj feet1 and is a desert4 ,a large proportion of the rain which falls in the region is caught by the mountains1 and especially by the higher mountains4 ,of this there is abundant proof in the distribution of vegetation and of springs4 ,the vegetation of the plain is exceedingly meager1 comprising only sparsely set grasses and shrubs1 and in favored spots the dwarf cedar of the ,west 7,juniperus occidentalis74 ,mount ,ellen1 which has a continuous ridge two miles long and more than #aa1jjj feet high1 bears cedar about its base1 mingled higher up with pion 7,pinus edulis71 and succeeded above by the yellow pine 7,p4 ponderosa71 spruce 7,abies ,douglasii71 fir 7,a4 ,engelmanni71 and aspen 7,populus tremuloides74 ,the pines are scattering1 but the cedars are close set1 and the firs are in dense groves4 ,the upper slopes where not timbered are matted with luxuriant grasses and herbs4 ,the summits are naked4 ,mount ,pennell sends a single peak only to the height of the ,ellen ridge4 ,its vegetation is nearly the same1 but the timber extends almost to the summit4 ,mount ,hillers is #fej feet lower4 ,its timber reaches to the principal summit1 but is less dense than on the higher mountains4 ,the range of trees is the same4 ,mount ,ellsworth1 #b1ejj feet lower than ,mount ,hillers1 bears neither fir1 spruce1 pine nor aspen4 ,cedar and pion climb to the summit1 but are not so thickly set as on the lower slopes of the larger mountains4 ,the grasses are less rank and grow in scattered bunches4 ,mount ,holmes1 a few feet lower1 has the same flora1 with the addition of a score of spruce trees1 high up on the northern flank4 ,its summits are bare4 ,in a word1 the luxuriance of vegetation1 and the annual rainfall1 of which it is the index1 are proportioned to the altitude4 ,consider now the forms of the mountain tops4 ,in ,figure #ee are pictured the summit forms of ,mount ,ellen4 ,the crests are rounded2 the slopes are uniform and smooth4 ,examination has shown that the constituent rocks are of varying degrees of hardness1 trachyte dikes alternating with sandstones and shales2 but these variations rarely find expression in the sculptured forms4 ,in ,figure #ef are the summit crags of ,mount ,holmes4 ,they are dikes of trachyte denuded by a discriminating erosion of their encasements of sandstone1 and carved in bold relief4 ,in virtue of their superior hardness they survive the general degradation4 ,illustration3 ,,fig4 #ee4--,the ,crest of ,mount ,ellen1 as seen from ,ellen ,peak4 ,illustration3 ,,fig4 #ef4--,the ,crest of ,mount ,holmes4 ,the other mountains are intermediate in the character of their sculpture4 ,mount ,pennell is nearly as smooth as ,mount ,ellen4 ,mount ,ellsworth is nearly as rugged as ,mount ,holmes4 ,one may ride to the crest of ,mount ,ellen and to the summit of ,mount ,pennell2 he may lead his sure-footed cayuse to the top of ,mount ,hillers2 but ,mounts ,ellsworth and ,holmes are not to be scaled by horses4 ,the mountaineer must climb to reach their summits1 and for part of the way use hands as well as feet4 ,in a word1 the ruggedness of the summits or the differentiation of hard and soft by sculpture1 is proportioned inversely to the altitude4 ,and rainfall1 which in these mountains depends directly on altitude1 is proportioned inversely to ruggedness4 ,the explanation of this coincidence depends on the general relations of vegetation to erosion4 ,we have seen that vegetation favors the disintegration of rocks and retards the transportation of the disintegrated material4 ,where vegetation is profuse there is always an excess of material awaiting transportation1 and the limit to the rate of erosion comes to be merely the limit to the rate of transportation4 ,and since the diversities of rock texture1 such as hardness and softness1 affect only the rate of disintegration 7weathering and corrasion7 and not the rate of transportation1 these diversities do not affect the rate of erosion in regions of profuse vegetation1 and do not produce corresponding diversities of form4 ,on the other hand1 where vegetation is scant or absent1 transportation and corrasion are favored1 while weathering is retarded4 ,there is no accumulation of disintegrated material4 ,the rate of erosion is limited by the rate of weathering1 and that varies with the diversity of rock texture4 ,the soft are eaten away faster than the hard2 and the structure is embodied in the topographic forms4 ,thus a moist climate by stimulating vegetation produces a sculpture independent of diversities of rock texture1 and a dry climate by repressing vegetation produces a sculpture dependent on those diversities4 ,with great moisture the law of divides is supreme2 with aridity1 the law of structure4 ,hence it is that the upper slopes of the loftier of the ,henry ,mountains are so carved as to conceal the structure1 while the lower slopes of the same mountains and the entire forms of the less lofty mountains are so carved as to reveal the structure2 and hence too it is that the arid plateaus of the ,colorado ,basin abound in cliffs and caons1 and offer facilities to the student of geological structure which no humid region can afford4 ,here too is the answer to the question so often asked1 8whether the rains and rivers which excavated the caons and carved the cliffs were not mightier than the rains and rivers of to-day40 ,aridity being an essential condition of this peculiar type of sculpture1 we may be sure that through long ages it has characterized the climate of the ,colorado ,basin4 ,a climate of great rainfall1 as ,professor ,powell has already pointed out in his 8,exploration of the ,colorado10 would have produced curves and gentle slopes in place of the actual angles and cliffs4 ,bad-lands4 ,mountain forms in general depend more on the law of divides than on the law of structure1 but their independence of structure is rarely perfect1 and it is difficult to discriminate the results of the two principles4 ,for the investigation of the workings of the law of divides it is better to select examples from regions which afford no variety of rock texture and are hence unaffected in their erosion by the law of structure4 ,such examples are found in bad-lands4 ,where a homogeneous1 soft rock is subjected to rapid degradation in an arid climate1 its surface becomes absolutely bare of vegetation and is carved into forms of great regularity and beauty4 ,in the neighborhood of the ,henry ,mountains1 the ,blue ,gate and ,tununk shales are of this character1 and their exposures afford many opportunities for the study of the principles of sculpture4 ,i was able to devote no time to them1 but in riding across them my attention was attracted by some of the more striking features1 and these ,i will venture to present1 although ,i am conscious that they form but a small part of the whole material which the bad-lands may be made to yield4 ,if we examine a bad-land ridge1 separating two drainage lines and forming a divide between them1 we find an arrangement of secondary ridges and secondary drainage lines1 similar to that represented in the diagram1 7,figure #eh47 ,illustration3 ,,fig4 #eg4--;,general view of the ,plateaus lying ,east of the ,henry ,mountains4 ,the general course of the main ridge being straight1 its course in detail is found to bear a simple relation to the secondary ridges4 ,wherever a secondary joins1 the main ridge turns1 its angle being directly toward the secondary4 ,the divide thus follows a zigzag course1 being deflected to the right or left by each lateral spur4 ,the altitude of the main ridge is correspondingly related to the secondary ridges4 ,at every point of union there is a maximum1 and in the intervals are saddles4 ,the maxima are not all equal1 but bear some relation to the magnitudes of the corresponding secondary ridges1 and are especially accented where two or more secondaries join at the same point4 7,see profile in ,figure #ei47 ,i conceive that the explanation of these phenomena is as follows3 ,the heads of the secondary drainage lines laid down in the diagram are in nature tolerably definite points4 ,the water which during rain converges at one of these points is there abruptly concentrated in volume4 ,above the point it is a sheet1 or at least is divided into many rills4 ,below it1 it is a single stream with greatly increased power of transportation and corrasion4 ,the principle of equal action gives to the concentrated stream a less declivity than to the diffused sheet1 and--what is especially important--it tends to produce an equal grade in all directions upward from the point of convergence4 ,the converging surface becomes hopper-shaped or funnel-shaped2 and as the point of convergence is lowered by corrasion1 the walls of the funnel are eaten back equally in all directions--except of course the direction of the stream4 ,the influence of the stream in stimulating erosion above its head is thus extended radially and equally through an arc of #ahj1 of which the center is at the point of convergence4 ,where two streams head near each other1 the influence of each tends to pare away the divide between them1 and by paring to carry it farther back4 ,the position of the divide is determined by the two influences combined and represents the line of equilibrium between them4 ,the influences being radial from the points of convergence1 the line of equilibrium is tangential1 and is consequently at right angles to a line connecting the two points4 ,thus1 for example1 if a1 b1 and c 7,figure #eh7 are the points of convergence at the heads of three drainage lines1 the divide line ed is at right angles to a line connecting a and b1 and the divides fd and gd are similarly determined4 ,the point d is simultaneously determined by the intersection of the three divide lines4 ,illustration3 ,,fig4 #eh4--;,ground plan of a ,bad-land ,ridge1 showing its relation to ,waterways4 ,the smooth lines represent ,divides4 ,,fig4 #ei4--,profile of the same ridge4 ,furthermore1 since that point of the line ed which lies directly between a and b is nearest to those points1 it is the point of the divide most subject to the erosive influences which radiate from a and b1 and it is consequently degraded lower than the contiguous portions of the divide4 ,the points d and e are less reduced2 and d1 which can be shown by similar reasoning to stand higher than the adjacent portion of either of the three ridges which there unite1 is a local maximum4 ,there is one other peculiarity of bad-land forms which is of great significance1 but which ,i shall nevertheless not undertake to explain4 ,according to the law of divides1 as stated in a previous paragraph1 the profile of any slope in bad-lands should be concave upward1 and the slope should be steepest at the divide4 ,the union or intersection of two slopes on a divide should produce an angle4 ,but in point of fact the slopes do not unite in an angle4 ,they unite in a curve1 and the profile of a drainage slope instead of being concave all the way to its summit1 changes its curvature and becomes convex4 ,figure #fj represents a profile from a to b of ,figure #eh4 ,from a to m and from b to n the slopes are concave1 but from m to n there is a convex curvature4 ,where the flanking slopes are as steep as represented in the diagram1 the convexity on the crest of a ridge has a breadth of only two or three yards1 but where the flanking slopes are gentle1 its breadth is several times as great4 ,it is never absent4 ,thus in the sculpture of the bad-lands there is revealed an exception to the law of divides1--an exception which cannot be referred to accidents of structure1 and which is as persistent in its recurrence as are the features which conform to the law1--an exception which in some unexplained way is part of the law4 ,our analysis of the agencies and conditions of erosion1 on the one hand1 has led to the conclusion that 7where structure does not prevent7 the declivities of a continuous drainage slope increase as the quantities of water flowing over them decrease2 and that they are great in proportion as they are near divides4 ,our observation1 on the other hand1 shows that the declivities increase as the quantities of water diminish1 up to a certain point where the quantity is very small1 and then decrease2 and that declivities are great in proportion as they are near divides1 unless they are very near divides4 ,evidently some factor has been overlooked in the analysis1--a factor which in the main is less important than the flow of water1 but which asserts its existence at those points where the flow of water is exceedingly small1 and is there supreme4 ,illustration3 ,,fig4 #fj4--;,cross-profile of a ,bad-land ,divide4 ,equal ,action and ,interdependence4 ,the tendency to equality of action1 or to the establishment of a dynamic equilibrium1 has already been pointed out in the discussion of the principles of erosion and of sculpture1 but one of its most important results has not been noticed4 ,of the main conditions which determine the rate of erosion1 namely1 quantity of running water1 vegetation1 texture of rock1 and declivity1 only the last is reciprocally determined by rate of erosion4 ,declivity originates in upheaval1 or in the displacements of the earth's crust by which mountains and continents are formed2 but it receives its distribution in detail in accordance with the laws of erosion4 ,wherever by reason of change in any of the conditions the erosive agents come to have locally exceptional power1 that power is steadily diminished by the reaction of rate of erosion upon declivity4 ,every slope is a member of a series1 receiving the water and the waste of the slope above it1 and discharging its own water and waste upon the slope below4 ,if one member of the series is eroded with exceptional rapidity1 two things immediately result3 first1 the member above has its level of discharge lowered1 and its rate of erosion is thereby increased2 and second1 the member below1 being clogged by an exceptional load of detritus1 has its rate of erosion diminished4 ,the acceleration above and the retardation below1 diminish the declivity of the member in which the disturbance originated2 and as the declivity is reduced the rate of erosion is likewise reduced4 ,but the effect does not stop here4 ,the disturbance which has been transferred from one member of the series to the two which adjoin it1 is by them transmitted to others1 and does not cease until it has reached the confines of the drainage basin4 ,for in each basin all lines of drainage unite in a main line1 and a disturbance upon any line is communicated through it to the main line and thence to every tributary4 ,and as any member of the system may influence all the others1 so each member is influenced by every other4 ,there is an interdependence throughout the system4 ,,iii4--,,systems ,,of ,,drainage4 ,to know well the drainage of a region two systems of lines must be ascertained--the drainage lines and the divides4 ,the maxima of surface on which waters part1 and the minima of surface in which waters join1 are alike intimately associated with the sculpture of the earth and with the history of the earth's structure2 and the student of either sculpture or history can well afford to study them4 ,in the following pages certain conditions which affect their permanence and transformations are discussed4 ,,the ,,stability ,,of ,,drainage ,,lines4 ,in corrasion the chief work is performed by the impact and friction of hard and heavy particles moved forward by running water4 ,they are driven against all sides of the channel1 but their tendency to sink in water brings them against the bottom with greater frequency and force than against the walls4 ,if the rate of wear be rapid1 by far the greater part of it is applied to the bottom1 and the downward corrasion is so much more powerful than the lateral that the effect of the latter is practically lost1 and the channel of the stream1 without varying the position of its banks1 carves its way vertically into the rock beneath4 ,it is only when corrasion is exceedingly slow that the lateral wear becomes of importance2 and hence as a rule the position of a stream bed is permanent4 ,the stability of drainage lines is especially illustrated in regions of displacement4 ,if a mountain is slowly lifted athwart the course of a stream1 the corrasion of the latter is accelerated by the increase of declivity1 and instead of being turned aside by the uplift1 it persistently holds its place and carves a channel into the mountain as the mountain rises4 ,for example the deep clefts which intersect the ,wasatch range owe their existence to the fact that at the time of the beginning of the uplift which has made the range1 there were streams flowing across the line of its trend which were too powerful to be turned back by the growing ridge4 ,the same relation has been shown by ,professor ,powell where the ,green ,river crosses the uplift of the ,uinta ,mountains1 and in many instances throughout the ,rocky ,mountain region it may be said that rivers have cut their way through mountains merely because they had established their courses before the inception of the displacement1 and could not be diverted by an obstruction which was thrown up with the slowness of mountain uplift4 ,,the ,,instability ,,of ,,drainage ,,lines4 ,the stability of waterways being the rule1 every case of instability requires an explanation2 and in the study of such exceptional cases there have been found a number of different methods by which the courses of streams are shifted4 ,the more important will be noted4 ,ponding4 ,when a mountain uplift crosses the course of a stream1 it often happens that the rate of uplift is too rapid to be equaled by the corrasion of the stream1 and the uprising rock becomes a dam over which the water still runs1 but above which there is accumulated a pond or lake4 ,whenever this takes place1 the pond catches all the dbris of the upper course of the stream1 and the water which overflows at the outlet having been relieved of its load is almost powerless for corrasion1 and cannot continue its contest with the uplift unless the pond is silted up with detritus4 ,as the uplift progresses the level of the pond is raised higher and higher1 until finally it finds a new outlet at some other point4 ,the original outlet is at once abandoned1 and the new one becomes a permanent part of the course of the stream4 ,as a rule it is only large streams which hold their courses while mountains rise2 the smaller are turned back by ponding1 and are usually diverted so as to join the larger4 ,the disturbances which divert drainage lines are not always of the sort which produce mountains4 ,the same results may follow the most gentle undulations of plains4 ,it required a movement of a few feet only to change the outlet of ,lakes ,michigan1 ,huron1 and ,superior from the ,illinois ,river to the ,st4 ,clair2 and in the tilting which turned ,lake ,winipeg from the ,mississippi to the ,nelson no abrupt slopes were produced4 ,if the entire history of the latter case were worked out1 it would probably appear that the ,saskatchewan ,river which rises in the ,rocky ,mountains beyond our northern boundary1 was formerly the upper course of the ,mississippi1 and that when1 by the rising of land in ,minnesota or its sinking at the north1 a barrier was formed1 the water was ponded and ,lake ,winipeg came into existence4 ,by the continuance of the movement of the land the lake was increased until it overflowed into ,hudson's ,bay2 and by its further continuance1 combined with the corrasion of the outlet1 the lake has been again diminished4 ,when eventually the lake disappears the revolution will be complete1 and the ,saskatchewan will flow directly to ,hudson's ,bay1 as it once flowed directly to the ,gulf of ,mexico4 7,see the 8,physical ,features of the ,valley of the ,minnesota ,river10 by ,general ,g4 ,k4 ,warren47 ,planation4 ,it has been shown in the discussion of the relations of transportation and corrasion that downward wear ceases when the load equals the capacity for transportation4 ,whenever the load reduces the downward corrasion to little or nothing1 lateral corrasion becomes relatively and actually of importance4 ,the first result of the wearing of the walls of a stream's channel is the formation of a flood-plain4 ,as an effect of momentum the current is always swiftest along the outside of a curve of the channel1 and it is there that the wearing is performed2 while at the inner side of the curve the current is so slow that part of the load is deposited4 ,in this way the width of the channel remains the same while its position is shifted1 and every part of the valley which it has crossed in its shiftings comes to be covered by a deposit which does not rise above the highest level of the water4 ,the surface of this deposit is hence appropriately called the flood-plain of the stream4 ,the deposit is of nearly uniform depth1 descending no lower than the bottom of the water-channel1 and it rests upon a tolerably even surface of the rock or other material which is corraded by the stream4 ,the process of carving away the rock so as to produce an even surface1 and at the same time covering it with an alluvial deposit1 is the process of planation4 ,it sometimes happens that two adjacent streams by extending their areas of planation eat through the dividing ridge and join their channels4 ,the stream which has the higher surface at the point of contact1 quickly abandons the lower part of its channel and becomes a branch of the other1 having shifted its course by planation4 ,the slopes of the ,henry ,mountains illustrate the process in a peculiarly striking manner4 ,the streams which flow down them are limited in their rate of degradation at both ends4 ,at their sources1 erosion is opposed by the hardness of the rocks2 the trachytes and metamorphics of the mountain tops are carved very slowly4 ,at their mouths1 they discharge into the ,colorado and the ,dirty ,devil1 and cannot sink their channels more rapidly than do those rivers4 ,between the mountains and the rivers1 they cross rocks which are soft in comparison with the trachyte1 but they can deepen their channels with no greater rapidity than at their ends4 ,the grades have adjusted themselves accordingly4 ,among the hard rocks of the mountains the declivities are great1 so as to give efficiency to the eroding water4 ,among the sedimentary rocks of the base they are small in comparison1 the chief work of the streams being the transportation of the trachyte dbris4 ,so greatly are the streams concerned in transportation1 and so little in downward corrasion 7outside the trachyte region71 that their grades are almost unaffected by the differences of rock texture1 and they pass through sandstone and shale with nearly the same declivity4 ,the rate of downward corrasion being thus limited by extraneous conditions1 and the instrument of corrasion--the dbris of the hard trachyte--being efficient1 lateral corrasion is limited only by the resistance which the banks of the streams oppose4 ,where the material of the banks is a firm sandstone1 narrow flood-plains are formed2 and where it is a shale1 broad ones4 ,in the ,gray ,cliff and ,vermilion ,cliff sandstones flat-bottomed caons are excavated2 but in the great shale beds broad valleys are opened1 and the flood-plains of adjacent streams coalesce to form continuous plains4 ,the broadest plains are as a rule carved from the thickest beds of shale1 and these are found at the top of the ,jura-,trias and near the base of the ,cretaceous4 ,where the streams from the mountains cross the ,blue ,gate1 the ,tununk1 or the ,flaming ,gorge shale at a favorable angle1 a plain is the result4 ,the plain which lies at the southern and western bases of ,mount ,hillers is carved chiefly from the ,tununk shale 7see ,figure #bg74 ,the plain sloping eastward from ,mount ,pennell 7,figure #cf7 is carved from the ,blue ,gate and ,tununk shales4 ,the ,lewis ,creek plain1 which lies at the western base of ,mount ,ellen1 is formed from the ,blue ,gate1 ,tununk1 and ,masuk shales1 and the planation which produced it has so perfectly truncated the ,tununk and ,blue ,gate sandstones that their outcrops cannot be traced 7,figures #fa1 #ci1 and #db74 ,the plain which truncates the ,crescent arch 7,figure #di7 is carved in chief part from the ,flaming ,gorge shale4 ,toward the east it is limited by the outcrops of the ,henry's ,fork conglomerate1 but toward the mountain it cuts across the edge of the same conglomerate and extends over ,tununk shale to the margin of the trachyte4 ,illustration3 ,,fig4 #fa4--;,cross-section of the ,lewis ,creek ,plain4 ,m1 ,masuk ,shale4 ,,bg1 ,blue ,gate ,group4 ,t1 ,tununk ,group4 ,,hf1 ,henry's ,fork conglomerate4 ,scale1 #a inch #d1jjj feet4 ,the streams which made these plains and which maintain them1 accomplish their work by a continual shifting of their channels2 and where the plains are best developed they employ another method of shifting--a method which in its proper logical order must be treated in the discussion of alluvial cones1 but which is practically combined in the ,henry ,mountains with the method of planation4 ,the supply of detritus derived from the erosion of the trachyte is not entirely constant4 ,not only is more carried out in one season than another and in one year than another1 but the work is accomplished in part by sudden storms which create great floods and as suddenly cease4 ,it results from this irregularity that the channels are sometimes choked by dbris1 and that by the choking of the channels the streams are turned aside to seek new courses upon the general plain4 ,the abandoned courses remain plainly marked1 and one who looks down on them from some commanding eminence can often trace out many stages in the history of the drainage4 ,where a series of streams emerge from adjacent mountain gorges upon a common plain1 their shiftings bring about frequent unions and separations1 and produce a variety of combinations4 ,illustration3 ,,fig4 #fb4--;,ideal sketch to illustrate the ,shifting of waterways on a slope of ,planation4 ,the accompanying sketch1 ,figure #fb1 is not from nature1 but it serves to illustrate the character of the changes4 ,the streams which issue from the mountain gorges a and b join and flow to z2 while that which issues at c flows alone to x4 ,an abandoned channel1 n1 shows that the stream from b was formerly united with that from c1 and flowed to x2 and another channel1 m1 shows that it has at some time maintained an independent course to y4 ,by such shiftings streams are sometimes changed from one drainage system to another2 the hypothetical courses1 x1 y1 and z1 may lead to different rivers1 and to different oceans4 ,an instance occurs on the western flank of the mountains4 ,one of the principal heads of ,pine ,alcove ,creek rises on the south slope of ,mount ,ellen and another on the northwest slope of ,mount ,pennell4 ,the two unite and flow southward to the ,colorado ,river4 ,they do not now cross an area of planation1 but at an earlier stage of the degradation they did2 and the portions of that plain which survive1 indicate by the direction of their slopes that one or both of the streams may have then discharged its water into ,lewis ,creek1 which runs northward to the ,dirty ,devil ,river4 ,as the general degradation of the region progresses the streams and their plains sink lower1 and eventually each plain is sunk completely through the shale whose softness made it possible4 ,so soon as the streams reach harder rock their lateral corrasion is checked1 and they are no longer free to change their ways4 ,wherever they chance to run at that time1 there they stay and carve for themselves caons4 ,portions of the deserted plains remain between the caons1 and having a durable capping of trachyte gravel are long preserved4 ,such stranded fragments abound on the slopes of the mountains1 and in them one may read many pages of the history of the degradation4 ,they form tabular hills with sloping tops and even profiles4 ,the top of each hill is covered with a uniform layer of gravel1 beneath which the solid rock is smoothly truncated4 ,the slope of the hill depends on the grade of the ancient stream1 and is independent of the hardness and dip of the strata4 ,the illustration represents a hill of planation on the north slope of ,mount ,ellsworth4 ,it is built of the ,gray ,cliff sandstone and ,flaming ,gorge shale1 inclined at angles varying from #be to #de2 but notwithstanding their variety of texture and dip the edges of the strata are evenly cut away1 so that their upper surface constitutes a plane4 ,the stream which performed this truncation afterward cut deeper into the strata and carved the lower table which forms the foreground of the sketch4 ,it has now abandoned this plain also and flows through a still deeper channel on the opposite side of the hill4 ,illustration3 ,,fig4 #fc4--;,a ,hill of ,planation4 ,the phenomena of planation are further illustrated in the region which lies to the northwest of the ,henry ,mountains4 ,tantalus and ,temple ,creeks1 rising under the edge of the ,aquarius ,plateau1 transport the trachyte of the plateau across the region of the ,waterpocket flexure to the ,dirty ,devil ,river4 ,their flood-plains are not now of great extent1 but when their drainage lines ran a few hundred feet higher they appear to have carved into a single plain a broad exposure of the ,flaming ,gorge shale1 which then lay between the ,waterpocket and ,blue ,gate flexures4 ,at the ,red ,gate where the ,dirty ,devil ,river passes from a district of trachyte plateaus to the district of the ,great ,flexures1 it follows for a few miles the outcrop of the ,shinarump shale1 and the remnants of its abandoned flood-plains form a series of terraces upon each bank4 ,small streams from the sides have cut across the benches and displayed their structure4 ,each one is carved from the rock in situ1 but each is covered by a layer of the rounded river gravel4 ,the whole are results of planation2 and they serve to connect the somewhat peculiar features of the mountain slopes with the ordinary terraces of rivers4 ,illustration3 ,,fig4 #fd4--;,ideal cross-section of a ,terraced ,river ,valley1 after ,hitchcock4 ,a1 ,b1 ,c1 ,d1 ,e1 and ,f1 ,alluvial deposits4 ,g1 ,indurated rock1 in situ4 ,river terraces as a rule are carved out1 and not built up4 ,they are always the vestiges of flood-plains1 and flood-plains are usually produced by lateral corrasion4 ,there are instances1 especially near the sea-coast1 of river-plains which have originated by the silting up of valleys1 and have been afterward partially destroyed by the same rivers when some change of level permitted them to cut their channels deeper2 and these instances1 conspiring with the fact that the surfaces of flood-plains are alluvial1 and with the fact that many terraces in glacial regions are carved from unconsolidated drift1 have led some ,american geologists into the error of supposing that river terraces in general are the records of sedimentation1 when in fact they record the stages of a progressive corrasion4 ,the ideal section of a terraced river valley which ,i reproduce from ,hitchcock 7,surface ,geology1 ,plate ,,xii1 figure #a7 regards each terrace as the remnant of a separate deposit1 built up from the bottom of the valley4 ,to illustrate my own idea ,i have copied his profile 7,figure #fe7 and interpreted its features as the results of lateral corrasion or planation1 giving each bench a capping of alluvium1 but constituting it otherwise of the prexistent material of the valley4 ,the prexistent material in the region of the ,henry ,mountains is always rock in situ1 but in the ,northern ,states it often includes glacial drift1 modified or unmodified4 ,there is a kindred error1 as ,i conceive1 involved in the assumption that the streams which occupied the upper and broader flood-plains of a valley were greater than those which have succeeded them4 ,they may have been1 or they may not4 ,in the process of lateral corrasion all the material that is worn from the bank has to be transported by the water1 and where the bank is high the work proceeds less rapidly than where it is low4 ,a stream which degrades its immediate valley more rapidly than the surrounding country is degraded 7and the streams which abound in terraces are of this character7 steadily increases the height of the banks which must be excavated in planation and diminishes the extent of its flood-plain2 and this might occur even if the volume of the stream was progressively increasing instead of diminishing4 ,illustration3 ,,fig4 #fe4--;,ideal cross-section of a ,terraced ,river ,valley1 regarded as a result of ,planation4 ,a1 ,b1 ,c1 c41 ,alluvial deposits4 ,g1 ,prexistent material from which the valley was excavated4 ,of the same order also is the mistake1 occasionally made of ignoring the excavation which a stream has performed1 and assuming that when the upper terraces were made the valley was as open as at present1 and the volume of flowing water was great enough to fill it4 ,alluvial ,cones4 ,wherever a stream is engaged in deposition instead of corrasion--wherever it deposits its load--there is a shifting of channel by a third process4 ,the deposition of sediment takes place upon the bottom of the channel and upon its immediate banks1 and this continues until the channel bottom is higher than the adjacent country4 ,the wall of the channel is then broken through at some point1 and the water abandons its old bed for one which is lower4 ,such occurrences belong to the histories of all river deltas1 and the devastation they have wrought at the mouths of large rivers has enforced attention to their phenomena and stimulated a study of their causes4 ,the same thing happens among the mountains4 ,wherever1 as in ,nevada and ,western ,utah1 the valleys are the receptacles of the detritus washed out from the mountains1 the foot-slopes of the mountains consist of a series of alluvial cones4 ,from each mountain gorge the products of its erosion are discharged into the valley4 ,the stream which bears the dbris builds up the bed of its channel until it is higher than the adjacent land and then abandons it1 and by the repetition of this process accumulates a conical hill of detritus which slopes equally in all directions from the mouth of the mountain gorge4 ,at one time or another the water runs over every part of the cone and leaves it by every part of its base2 and it sometimes happens that the opposite slopes of the cone lead to different drainage systems4 ,an illustration may be seen in ,red ,rock ,pass at the north end of ,cache ,valley1 ,idaho4 ,lake ,bonneville1 the ancient expansion of ,great ,salt ,lake1#f here found outlet to the basin of the ,columbia1 and the channel carved by its water is plainly marked4 ,for a distance of twelve miles the bed of the channel is nearly level1 with a width of a thousand feet4 ,midway1 ,marsh ,creek enters it from the east1 and has built an alluvial cone which extends to the opposite bank and divides it into two parts4 ,in the construction of the cone ,marsh ,creek has flowed alternately to the north and to the south1 being in one case a tributary to the ,snake and ,columbia ,rivers and to the ,pacific ,ocean1 and in the other to the ,bear ,river and ,great ,salt ,lake4 ,so far as the creek is known to white men it is a tributary of the ,snake1 but an irrigating ditch that has been dug upon its cone carries part of its water to the ,bear4 ,footnote #f3 ,lake ,bonneville is described in volume ,,iii 7,geology7 of the 8,u4 ,s4 ,geog4 ,surveys ,west of the #ajjth ,meridian10 pp4 #hh-ajd2 and less fully in the ,american ,naturalist for ,november1 #ahgf1 and the ,american ,journal of ,science for ,march1 #ahgf1 p4 #bbh4 ,see also ,johnson's ,cyclopedia1 article 8,sevier ,lake40 ,another illustration exists at the mouth of the ,colorado ,river4 ,as has been shown by ,blake in the fifth volume of the ,pacific ,railroad ,reports 7p4 #bcf71 the delta of the ,colorado--or in other words the alluvial cone which is built at its mouth--has extended itself completely across the ,gulf of ,california1 severing the upper end from the lower and from the ocean1 and converting it into a lake4 ,in continuing the upbuilding of the delta the river has flowed alternately into the lower gulf and into its severed segment4 ,at the present day its mouth opens to the lower gulf2 but at rare intervals a portion of its water runs by the channel known as 8,new ,river0 to the opposite side of the delta4 ,while it is abandoned by the river the lake basin is dry1 and it is known to human history only as the ,colorado ,desert4 ,its bottom1 which is lower than the surface of the ocean1 is strewn with the remains of the life its waters sustained1 and its beaches are patiently awaiting the cycle of change which is slowly but surely preparing to restore to them their parent waves4 ,illustration3 ,,fig4 #ff4--;,cross-section of inclined strata1 to illustrate ,monoclinal ,shifting of waterways4 ,monoclinal ,shifting4 ,in a fourth manner drainage lines are unstable4 ,in a region of inclined strata there is a tendency on the part of streams which traverse soft beds to continue therein1 and there is a tendency to eliminate drainage lines from hard beds4 ,in ,figure #ff1 ,s represents a homogeneous soft bed1 and ,h and ,k1 homogeneous hard beds4 ,a and ,b are streams flowing through channels opened in the soft rock1 and in the hard4 ,as the general degradation progresses the stream at a abrades both sides of its channel with equal force2 but it fails to corrade them at equal rates because of the inequality of the resistance4 ,it results that the channel does not cut its way vertically into the hard rock1 but works obliquely downward without changing its relation to the two beds2 so that when the degradation has reached the stage indicated by the dotted line1 the stream flows at a1 having been shifted horizontally by circumstances dependent on the dip and order of the strata4 ,at the same time the stream at ,b1 encountering homogeneous material1 cuts its way vertically downward to b2 and a continuance of the process carries it completely through the hard rock and into the soft4 ,once in the soft it tends like the other streams to remain there2 and in the course of time it finds its way to the lower edge and establishes a channel like that at ,a4 ,illustration3 ,,fig4 #fg4--;,ground plan of outcrops of inclined strata1 to illustrate the results of ,monoclinal ,shifting4 ,the effect of this process on the course of a stream which runs obliquely across inclined beds is shown in ,figure #fg4 ,the outcrops of a series of hard and soft strata1 ,h1 ,h1 ,h and ,s1 ,s1 are represented in ground plan1 and the direction of their dip is indicated by the arrow4 ,supposing that a stream is thrown across them in the direction of the dotted lines and that the land is then degraded1 the following changes will take place4 ,the portion of the stream from c to d will sink through the soft rock down to the surface of the hard1 and then follow down the slope of the hard1 until at last its whole course will be transferred to the line of separation between the two1 and its position 7with reference to the outcrops which will then have succeeded the original7 will be represented by the line g c4 ,the portion from e to d sinking first through the hard bed and then through the soft1 will be deflected in the same manner to the position e h g4 ,the points e and c will retain their original relations to the strata4 ,the same changes will affect the portion from e to f2 and the original oblique course will be converted into two sets of courses1 of which one will follow the strike of the strata and the other will cross the strike at right angles4 ,the character of these changes is independent of the direction of the current4 ,they are not individually of great amount1 and they do not often divert streams from one drainage system to another nor change their general directions4 ,their chief effects are seen in the details of drainage systems and in the production of topographic forms4 ,the tendency of hard strata to rid themselves of waterways and of soft strata to accumulate them1 is a prime element of the process which carves hills from the hard and valleys from the soft4 ,where hard rocks are crossed by waterways they cannot stand higher than the adjacent parts of the waterways2 but where they are not so crossed they become divides1 and the 8law of divides0 conspires with the 8law of structure0 to carve eminences from them4 ,the tendency of waterways to escape from hard strata and to abide in soft1 and their tendency to follow the strike of soft strata and to cross hard at right angles1 are tendencies only and do not always prevail4 ,they are opposed by the tendency of drainage lines to stability4 ,if the dip of the strata is small1 or if the differences of hardness are slight1 or if the changes of texture are gradual instead of abrupt1 monoclinal shifting is greatly reduced4 ,waterpocket ,caon is one of the most remarkable of monoclinal valleys2 and it serves to illustrate both the rule of monoclinal shifting and its exception4 ,the principal bed of soft rock which outcrops along the line of the ,waterpocket flexure is the ,flaming ,gorge shale1 having a thickness of more than one thousand feet4 ,through nearly the whole extent of the outcrop a valley is carved from it1 but the valley is not a unit in drainage4 ,at the north it is crossed by the ,dirty ,devil ,river and by ,temple and ,tantalus ,creeks1 and the adjacent portions slope toward those streams4 ,at the south it is occupied for thirty miles by a single waterway--the longest monoclinal drainage line with which ,i am acquainted4 ,the valley here bears the name of ,waterpocket ,caon1 and descends all the way from the ,masuk ,plateau to the ,colorado ,river4 ,the upper part of the caon is dry except in time of rain1 but the lower carries a perpetual stream known as ,hoxie ,creek4 ,whatever may have been the original meanderings of the latter they are now restrained1 and it is limited to the narrow belt in which the shale outcrops4 ,as the caon is worn deeper the channel steadily shifts its position down the slope of the underlying ,gray ,cliff sandstone1 and carves away the shale4 ,but there is one exceptional point where it has not done this4 ,when the bottom of the caon was a thousand feet higher the creek failed1 at a place where the dip of the strata was comparatively small1 to shift its channel as it deepened it1 and began to cut its way into the massive sandstone4 ,having once entered the hard rock it could not retreat but sank deeper and deeper1 carving a narrow gorge through which it still runs making a detour from the main valley4 ,the traveler who follows down ,waterpocket ,caon now comes to a place where the creek turns from the open caon of the shale and enters a dark cleft in the sandstone4 ,he can follow the course of the water 7on foot71 and will be repaid for the wetting of his feet by the strange beauty of the defile4 ,for nearly three miles he will thread his way through a gorge walled in by the smooth1 curved faces of the massive sandstone1 and so narrow and devious that it is gloomy for lack of sunlight2 and then he will emerge once more into the open caon4 ,or if he prefer he can keep to his saddle1 to the open daylight1 and to the outcrop of the shale1 and riding over a low divide can reach the mouth of the gorge in half the distance4 ,illustration3 ,,fig4 #fh4--,waterpocket ,caon and the ,horseshoe ,bend of ,hoxie ,creek4 ,,the ,,stability ,,of ,,divides4 ,the rain drops which fall upon the two sides of a divide flow in opposite directions4 ,however near to the dividing line they reach the earth the work of each is apportioned to its own slope4 ,it disintegrates and transports the material of its own drainage slope only4 ,the divide is the line across which no water flows--across which there is no transportation4 ,it receives the minimum of water1 for it has only that which falls directly upon it1 and every other point receives in addition that which flows from higher points4 ,it is higher than the surfaces which adjoin it1 and since less water is applied to its degradation it tends to remain higher4 ,it tends to maintain its position4 ,opposed to this tendency there are others which lead to ,,the ,,instability ,,of ,,divides1 and which will now be considered4 ,ponding1 ,planation1 and ,alluviation4 ,whenever by ponding1 a stream or a system of streams which have belonged to one drainage system are diverted so as to join another there is coincidently a change of divides4 ,the general divide between the two systems is shifted from one side to the other of the area which changes its allegiance4 ,the line which was formerly the main divide becomes instead a subordinate divide separating portions of the drainage system which has increased its area2 and on the other hand a line which had been a subordinate divide is promoted to the rank of a main divide4 ,in like manner the shifting of streams from one system of drainage to another by the extension of flood-plains1 or by the building of alluvial cones or deltas1 involves a simultaneous shifting of the divides which bound the drainage systems4 ,the changes which are produced by these methods are per saltum4 ,when a pond or lake opens a new outlet and abandons its old one there is a short interregnum during which the drainage is divided between the two outlets1 and the watershed separating the drainage systems is double4 ,but in no other sense is the change gradual4 ,the divide occupies no intermediate positions between its original and its final4 ,and the same may be said of the changes by planation and alluviation4 ,in each case a tract of country is transferred bodily from one river system to another1 and in each case the watershed makes a leap4 ,but there are other methods of change1 by which dividing lines move slowly across the land2 and to these we will proceed4 ,monoclinal ,shifting4 ,in regions of inclined strata1 the same process which gathers the waterways into the outcrops of the softer beds converts the outcrops of the harder into divides4 ,as the degradation progresses the waterways and divides descend obliquely and retain the same relations to the beds4 ,the waterways continuously select the soft because they resist erosion feebly1 and the watersheds as continuously select the hard because they resist erosion strongly4 ,if the inclination of the strata is gentle1 each hard bed becomes the cap of a sloping table bounded by a cliff1 and the erosion of the cliff is by sapping4 ,the divide is at the brow of the cliff1 and as successive fragments of the hard rock break away and roll down the slope the divide is shifted4 ,the process is illustrated in the ,pink ,cliffs of ,southern ,utah4 ,they face to the south1 and their escarpment is drained by streams flowing to the ,colorado4 ,the table which they limit inclines to the north and bears the headwaters of the ,sevier4 ,as the erosion of the cliffs steadily carries them back and restricts the table1 the drainage area of the ,colorado is increased and that of the 8,great ,basin01 to which the ,sevier ,river is tributary1 is diminished4 ,illustration3 ,,fig4 #fi4--;,ideal cross-section of inclined strata1 to show the ,shifting of ,divides in ,cliff ,erosion4 ,successive positions of a divide are indicated at a1 b1 and c4 ,unequal and ,equal ,declivities4 ,illustration3 ,,fig4 #gj4--;,cross-profile of a bad-land divide separating slopes of ,unequal ,declivity4 ,two stages of erosion are indicated1 to illustrate the horizontal shifting of the divide4 ,in homogeneous material1 and with equal quantities of water1 the rate of erosion of two slopes depends upon their declivities4 ,the steeper is degraded the faster4 ,it is evident that when the two slopes are upon opposite sides of a divide the more rapid wearing of the steeper carries the divide toward the side of the gentler4 ,the action ceases and the divide becomes stationary only when the profile of the divide has been rendered symmetric4 ,it is to this law that bad-lands owe much of their beauty4 ,they acquire their smooth curves under what ,i have called the 8law of divides01 but the symmetry of each ridge and each spur is due to the law of equal declivities4 ,by the law of divides all the slopes upon one side of a ridge are made interdependent4 ,by the law of equal declivities a relation is established between the slopes which adjoin the crest on opposite sides1 and by this means the slopes of the whole ridge1 from base to base1 are rendered interdependent4 ,one result of the interdependence of slopes is that a bad-land ridge separating two waterways which have the same level1 stands midway between them2 while a ridge separating two waterways which have different levels1 stands nearer to the one which is higher4 ,it results also that if one of the waterways is corraded more rapidly than the other the divide moves steadily toward the latter1 and eventually1 if the process continues1 reaches it4 ,when this occurs1 the stream with the higher valley abandons the lower part of its course and joins its water to that of the lower stream4 ,thus from the shifting of divides there arises yet another method of the shifting of waterways1 a method which it will be convenient to characterize as that of abstraction4 ,a stream which for any reason is able to corrade its bottom more rapidly than do its neighbors1 expands its valley at their expense1 and eventually 8abstracts0 them4 ,and conversely1 a stream which for any reason is able to corrade its bottom less rapidly than its neighbors1 has its valley contracted by their encroachments and is eventually 8abstracted0 by one or the other4 ,the diverse circumstances which may lead to these results need not be enumerated1 but there is one case which is specially noteworthy on account of its relation to the principles of sculpture4 ,suppose that two streams which run parallel and near to each other corrade the same material and degrade their channels at the same rate4 ,their divide will run midway4 ,but if in the course of time one of the streams encounters a peculiarly hard mass of rock while the other does not1 its rate of corrasion above the obstruction will be checked4 ,the unobstructed stream will outstrip it1 will encroach upon its valley1 and will at last abstract it2 and the incipient corrasion of the hard mass will be stopped4 ,thus by abstraction as well as by monoclinal shifting1 streams are eliminated from hard rocks4 ,rsum4--,there is a tendency to permanence on the part of drainage lines and divides1 and they are not displaced without adequate cause4 ,hence every change which is known to occur demands and admits of an explanation4 7a7 ,there are four ways in which abrupt changes are made4 ,streams are diverted from one drainage system to another1 and the watersheds which separate the systems are rearranged1 7#a7 by ponding1 due to the elevation or depression of portions of the land2 7#b7 by planation1 or the extension of flood-plains by lateral corrasion2 7#c7 by alluviation1 or in the process of building alluvial cones and deltas2 and 7#d7 by abstraction4 7b7 ,there are two ways in which gradual changes are effected3 7#a7 ,when the rock texture is variable1 it modifies and controls by monoclinal shifting the distribution in detail of divides and waterways4 7#b7 ,when the rock texture is uniform1 the positions of divides are adjusted in accordance with the principle of equal declivities4 ,the abrupt changes are of geographic import2 the gradual1 of topographic4 ,the methods which have been enumerated are not the only ones by which drainage systems are modified1 but they are the chief4 ,very rarely streams are 8ponded0 and diverted to new courses through the damming of their valleys by glaciers or by volcanic ejecta or by land-slips4 ,more frequently they are obstructed by the growing alluvial cones of stronger streams1 but only the smallest streams will yield their 8right of way0 for such cause1 and the results are insignificant4 ,the rotation of the earth1 just as it gives direction to the trade-winds and to ocean currents1 tends to deflect rivers4 ,in the southern hemisphere streams are crowded against their left banks and in northern against the right4 ,but this influence is exceedingly small4 ,mr4 ,ferrel's investigations show that in latitude #de and for a current velocity of ten miles an hour1 it is measured by less than one twenty-thousandth part of the weight of the water 7,american ,journal of ,science1 ,january1 #ahfa74 ,if its effects are ever appreciable it must be where lateral corrasion is rapid2 and even there it is probable that the chief result is an inclination of the flood-plain toward one bank or the other1 amounting at most to two or three minutes4 ,,consequent ,,and ,,inconsequent ,,drainage4 ,if a series of sediments accumulated in an ocean or lake be subjected to a system of displacements while still under water1 and then be converted to dry land by elevation en masse or by the retirement of the water1 the rains which fall on them will inaugurate a drainage system perfectly conformable with the system of displacements4 ,streams will rise along the crest of each anticlinal1 will flow from it in the direction of the steepest dip1 will unite in the synclinals1 and will follow them lengthwise4 ,the axis of each synclinal will be marked by a watercourse2 the axis of each anticlinal by a watershed4 ,such a system is said to be consequent on the structure4 ,if however a rock series is affected by a system of displacements after the series has become continental1 it will have already acquired a system of waterways1 and provided the displacements are produced slowly the waters will not be diverted from their accustomed ways4 ,the effect of local elevation will be to stimulate local corrasion1 and each river that crosses a line of uplift will inch by inch as the land rises deepen its channel and valorously maintain its original course4 ,it will result that the directions of the drainage lines will be independent of the displacements4 ,such a drainage system is said to be antecedent to the structure4 ,but if in the latter case the displacements are produced rapidly the drainage system will be rearranged and will become consequent to the structure4 ,it has frequently happened that displacements formed with moderate rapidity have given rise to a drainage system of mixed character in which the courses of the larger streams are antecedent and those of the smaller are consequent4 ,there is a fourth case4 ,suppose a rock series that has been folded and eroded to be again submerged1 and to receive a new accumulation of unconforming sediments4 ,suppose further that it once more emerges and that the new sediments are eroded from its surface4 ,then the drainage system will have been given by the form of the upper surface of the superior strata1 but will be independent of the structure of the inferior series1 into which it will descend vertically as the degradation progresses4 ,such a drainage system is said to be superimposed by sedimentation upon the structure of the older series of strata4 ,fifth4 ,the drainage of an alluvial cone or of a delta is independent of the structure of the bed-rock beneath2 and if in the course of time erosion takes the place of deposition and the alluvial formation is cut through1 the drainage system which is acquired by the rocks beneath is not consequent upon their structure but is superimposed by alluviation4 ,sixth4 ,the drainage of a district of planation is independent of the structure of the rock from which it is carved2 and when in the progress of degradation the beds favorable to lateral corrasion are destroyed and the waterways become permanent1 their system may be said to be superimposed by planation4 ,in brief1 systems of drainage1 in their relation to structure1 are 7,a7 consequent 7a7 by emergence1 when the displacements are subaqueous1 and 7b7 by sudden displacement2 7,b7 antecedent2 and 7,c7 superimposed 7a7 by sedimentation1 or subaqueous deposition1 7b7 by alluviation1 or subarial deposition1 and 7c7 by planation4 ,,the ,,drainage ,,of ,,the ,,henry ,,mountains is consequent on the laccolitic displacements4 ,the uplifting of a laccolite1 like the upbuilding of a volcanic cone1 is an event of so rapid progress that the corrasion of a stream bed cannot keep pace with it4 ,we do not know that the site of the mountains was dry land at the time of their elevation2 but if it was1 then whatever streams crossed it were obstructed and turned from their courses4 ,if it was not1 there were no prexistent waterways1 and the new ones1 formed by the first rain which fell upon the domes of strata1 radiated from the crests in all directions4 ,the result in either case would be the same1 and we cannot determine from the present drainage system whether the domes were lifted from the bed of the ,tertiary lake or arose after its subsidence4 ,but while the drainage of the ,henry ,mountains is consequent as a whole1 it is not consequent in all its details1 and the character of its partial inconsequence is worthy of examination4 ,let us begin with the simplest case4 ,the drainage system of ,mount ,ellsworth is more purely consequent than any other with which ,i am acquainted4 ,in the accompanying chart the point c marks the crest of the ,ellsworth dome2 the inner circle represents the line of maximum dip of the arching strata and the outer circle the limit of the disturbance4 ,it will be seen that all the waterways radiate from the crest and follow closely the directions in which the strata incline4 ,at a the ,ellsworth arch touches that of ,mount ,holmes and at b that of ,mount ,hillers2 and the effect of the compound inclination is to modify the directions of a few of the waterways4 ,illustration3 ,,fig4 #ga4--;,drainage system of the ,ellsworth ,arch4 ,turning now to ,mount ,holmes1 we find that its two domes are not equally respected by the drainage lines4 ,the crest of the ,greater arch 7see ,figure #gb7 is the center of a radiating system1 but the crest of the ,lesser arch is not2 and waterways arising on the ,greater traverse the ,lesser from side to side4 ,more than this1 a waterway after following the margin of the ,lesser arch turns toward it and penetrates the flank of the arch for some distance4 ,in a word1 the drainage of the ,greater arch is consequent on the structure1 while the drainage of the ,lesser arch is inconsequent4 ,illustration3 ,,fig4 #gb4--;,drainage system of the ,holmes ,arches4 ,there are at least two ways in which this state of affairs may have arisen4 ,first1 the ,greater arch may have been lifted so long before the ,lesser that its waterways were carved too deeply to be diverted by the gentle flexure of the latter4 ,the drainage of the ,lesser would in that case be classed as antecedent4 ,if the ,lesser arch were first formed and carved1 the lifting of the ,greater might throw a stream across its summit2 but it could not initiate the waterways which skirt the slopes of the ,lesser1 especially if those slopes were already furrowed by streams which descended them4 ,if the establishment of the drainage system depended on the order of uplift1 the ,greater arch is surely the older4 ,second1 the drainage of the ,lesser arch may have been imposed upon it by planation at a very late stage of the degradation4 ,whatever was the origin of the arches1 and whatever was the depth of cover which they sustained1 the ,greater is certain to have been a center of drainage from the time of its formation4 ,when it was first lifted it became a drainage center because it was an eminence2 and afterward it remained an eminence because it was a drainage center4 ,when in the progress of the denudation its dikes were exposed1 their hardness checked the wear of the summit and its eminence became more pronounced4 ,it was perhaps at about this time that the last of the ,cretaceous rocks were removed from the summits and slopes of the two arches and the ,flaming ,gorge shale was laid bare1 and so soon as this occurred the conditions for lateral corrasion were complete4 ,with trachyte in the peaks and shale upon the slopes planation would naturally result1 and a drainage system would be arranged about the dikes as a center without regard to the curves of the strata4 ,the subsequent removal of the shale would impart its drainage to the underlying sandstones4 ,either hypothesis is competent to explain the facts1 but the data do not warrant the adoption of one to the exclusion of the other4 ,the waterways of the ,lesser arch may be either antecedent1 or superimposed by planation4 ,the ,greater arch may have been the first to rise or the last4 ,the drainage of ,mount ,hillers is consequent to the main uplift and to the majority of the minor1 but to the ,pulpit arch it is inconsequent4 ,in this case there is no question that the arch has been truncated by planation4 7,figure #gc47 ,the ,hillers dome1 rising five times as high as the ,pulpit1 became the center of drainage for the cluster1 and the trachyte-laden streams which it sent forth were able to pare away completely the lower arch while it was still unprotected by the hardness of its nucleus4 ,the foot-plain of ,mount ,hillers1 which extends unbroken to the outcrop of the ,henry's ,fork conglomerate1 is continued on several lines across the ,pulpit arch1 although in the intervals the central area is deeply excavated4 ,the planation stage is just completed1 and an epoch of fixed waterways is inaugurated4 ,illustration3 ,,fig4 #gc4--;,cross-section of the ,pulpit ,arch1 showing its truncation4 ,the drainage of ,mount ,pennell is consequent in regard to the main uplift1 but inconsequent to some of the minor4 ,a stream which rises on the north flank not merely runs across one of the upper series of laccolites1--a companion to the ,sentinel1--but has cut into it and divided it nearly to the base4 ,it is probable that the position of the waterway was fixed by planation1 but no remnant of the plain was seen4 ,too little is known of the structure of the central area of ,mount ,ellen to assert its relation to the drainage4 ,about its base there are five laccolites which have lost all or nearly all their cover1 and each of these is a local center of drainage1 avoided by the streams which head in the mountain crest4 ,four others have been laid bare at a few points only1 and these are each crossed by one or two streams from higher levels4 ,the remainder are not exposed at all1 and their arches are crossed by numerous parallel streams4 ,the ,crescent arch is freshly truncated by planation1 and the ,dana and ,maze bear proof that they have at some time been truncated4 ,the laccolites which stand highest with reference to the general surface are exempt from cross-drainage1 and the arches which lie low are completely overrun4 ,if we go back in imagination to a time when the erosion of the mountain was so little advanced that the stream beds were three thousand feet higher than they now are1 we may suppose that very little trachyte was laid bare4 ,as the surface was degraded and a few laccolites were exposed1 it would probably happen that some of the then existing streams would be so placed as to run across the trachyte4 ,but being unarmed as yet by the dbris of similar material they would corrade it very slowly2 and the adjoining streams having only shale to encounter1 would so far outstrip them as eventually to divert them by the process of 8abstraction04 ,in this way the first-bared laccolites might be freed from cross-drainage and permitted to acquire such radiating systems of waterways as we find them to possess4 ,at a later stage when trachyte was exposed at many points and all streams were loaded with its waste1 the power to corrade was increased1 and the lower-lying laccolites could not turn aside the streams which overran them4 ,the work of planation is so frequently seen about the flanks of the ,henry ,mountains that there seems no violence in referring all the cross-drainage of lateral arches to its action2 and if that is done the history of the erosion of the mountains takes the following form3 ,when the laccolites were intruded1 the mounds which they uplifted either rose from the bed of a lake or else turned back all streams which crossed their sites2 and in either case they established upon their flanks a new and 8consequent0 set of waterways4 ,the highest mounds became centers of drainage1 and sent their streams either across or between the lower4 ,all the streams of the disturbed region rose within it and flowed outward4 ,the degradation of the mounds probably began before the uplift was complete1 but of this there is no evidence4 ,as it proceeded the convex forms of the mounds were quickly obliterated and concave profiles were substituted4 ,the rocks which were first excavated were not uniform in texture1 but they were all sedimentary and were soft as compared to the trachyte4 ,the ,tertiary and probably the ,upper ,cretaceous were removed from the summits before any of the igneous rocks were brought to light1 and during their removal the tendency of divides to permanence kept the drainage centers or maxima of surface at substantially the same points4 ,when at length the trachyte was reached its hardness introduced a new factor4 ,the eminences which contained it were established more firmly as maxima1 and their rate of degradation was checked4 ,with the checking of summit degradation and the addition of trachyte to the transported material1 planation began upon the flanks1 and by its action the whole drainage has been reformed4 ,one by one the lower laccolites are unearthed1 and each one adds to the complexity and to the permanence of the drainage4 ,if the displacements were completed before the erosion began1 the mountains were then of greater magnitude than at any later date4 ,before the igneous nuclei were laid bare and while sedimentary rocks only were subject to erosion1 the rate of degradation was more rapid than it has been since the hardness and toughness of the trachyte have opposed it4 ,if the surrounding plain has been worn away at a uniform rate1 the height of the mountains 7above the plain7 must have first diminished to a minimum and afterward increased4 ,the minimum occurred at the beginning of the erosion of the trachyte1 and at that time the mountains may even have been reduced to the rank of hills4 ,they owe their present magnitude1 not to the uplifting of the land in ,middle ,tertiary time1 but to the contrast between the incoherence of the sandstones and shales of the ,mesozoic series and the extreme durability of the laccolites which their destruction has laid bare4 ,and if the waste of the plain shall continue at a like uniform rate in the future1 it is safe to prophesy that the mountains will for a while continue to increase in relative altitude4 ,the phase which will give the maximum resistance to degradation has been reached in none of the mountains1 except perhaps ,mount ,hillers4 ,in ,mount ,ellen the laccolites of the upper zone only have been denuded2 the greater masses which underlie them will hold their place more stubbornly4 ,the main bodies of ,mounts ,ellsworth1 ,holmes1 and ,pennell are unassailed1 and the present prominence of their forms has been accomplished simply by the valor of their skirmish lines of dikes and spurs4 ,in attaching to the least of the peaks the name of my friend ,mr4 ,holmes1 ,i am confident that ,i commemorate his attainments by a monument which will be more conspicuous to future generations and races than it is to the present4 ,,chapter ,,vi4 ,,economic4 ,there is little to add to what has already been said of the economic value of the mountains1 and this chapter is hardly more than a regrouping of facts scattered through those that precede4 ,coal4--,possibly some valuable though restricted deposit was overlooked2 but it is safe to say that no thick and continuous bed will be found4 ,the ,cretaceous sandstones all contain thin and local beds--enough to mark them as coal-bearing rocks--but there are no seams of value4 ,the best outcrop was seen in the bank of the south branch of ,lewis ,creek where it crosses the upturned edge of the ,blue ,gate sandstone4 ,the seam has a thickness of four feet only1 and is not well disposed for mining4 ,but if the ,cretaceous coals were well developed it is to be doubted if they would ever be used4 ,they could have no local market4 ,they could not be carried to the east or south on account of the caons4 ,if taken northward they would have to compete with the coal of ,castle ,valley1 which is more convenient and very abundant4 ,if taken westward to the metal mines of ,nevada and ,western ,utah they would be undersold by the more accessible coals found on the headwaters of the ,virgin ,river and ,kanab ,creek1 and even by those of the ,kaiparowits ,plateau4 ,the ,gypsum and ,building ,stones of the region need not be described4 ,they are plentiful in many parts of ,utah1 and however abundant in this remote place can never be in demand4 ,gold1 ,silver1 etc4--,three parties of 8prospectors0 have at different times made unsuccessful search for metalliferous veins4 ,in the course of my survey ,i spent more than a month's time among the crystalline and metamorphic formations of the mountain tops1 and although directing my attention constantly to the rocks1 did not discover a fissure vein4 ,combining these negative data with certain theoretic considerations which are set forth in the fourth chapter1 ,i am led to the very confident opinion that the essential conditions for the production of fissure veins have not existed in the ,henry ,mountains1 and hence that there are no valuable deposits of the precious metals4 ,the same theoretic considerations apply to other mountains of the same character1 and ,i venture to predict that gold and silver will not be found in paying quantity in ,navajo ,mountain1 the ,sierra la ,sal1 the ,sierra ,abajo1 the ,sierra ,carisso1 or the ,sierra ,la ,lata4 ,agricultural ,land4--,bowl ,creek1 both branches of ,lewis ,creek1 and the south branch of ,trachyte ,creek can readily be led to tracts of land sufficiently level for farming1 and each furnishes enough water to irrigate several hundred acres4 ,it is possible that these tracts will prove useful for farming1 but they lie a little too high to be assured of a favorable climate4 ,the lowest has an altitude of #f1jjj1 and the highest of #f1hjj feet4 ,grazing ,land4--,above the altitude of #g1ejj feet there are many tracts of good grass1 available for grazing through the greater part of the year but covered by snow in the winter4 ,below that level there is a greater area of inferior grass1 available through the whole year4 ,by using one portion in summer and the other in winter the mountains could be made to give permanent support to a herd of #c1jjj or #d1jjj cattle4 ,with such overstocking as is often practiced in ,utah they may subsist #aj1jjj animals for one or two years4 ,timber4--,the trees worthy to be classed as timber are of three species--fir 7,abies ,engelmanni71 ,douglass ,spruce 7,a4 ,douglasii71 and yellow pine 7,pinus ponderosa74 ,the pine is the most valuable and the fir the most abundant4 ,the fir grows upon the mountain slopes1 above the level of #g1ejj feet and forms thick-set forests4 ,the total area which it covers is not far from twenty-five square miles4 ,the spruce mingles with the fir at the lower edges of the forests2 and the pine forms a few open groves a little lower down the slopes4 ,it is to be doubted if the trees will ever be cut4 ,other timber of the same quality and superior in quantity lies between it and the settlements1 and neither railroad nor mine nor town is likely to create a local demand4 ,coal1 building stone1 gypsum1 and timber have no value for lack of a market1 either present or prospective2 gold and silver are not found2 and there is little or no land that can be successfully farmed4 ,only for grazing have the mountains a money value4 ,,index4 ,abajo ,mountains1 #fg1 #fi1 #aeb ,agricultural lands1 #aeb ,alluvial cones and alluviation1 #acc1 #aci ,alpine sculpture1 #cf1 #ch ,altitudes of peaks and passes1 #c1 #aag ,analogues of the laccolite1 #ih ,ancient rivers no larger than modern1 #acc ,antecedent drainage1 #adc ,arch1 ,bowl ,creek1 #de 1 ,crescent1 #dd 1 ,dana1 #dc 1 ,g1 #dc 1 ,maze1 #dd 1 ,pulpit1 #cc1 #adg ,arches1 ,forces which produced laccolitic1 #hg ,aridity favorable to geological examination1 #b1 #ih of the ,colorado ,basin in former times1 #abj ,aubrey ,sandstone1 #h ,bad-lands1 ,sculpture of1 #abj1 #adj ,bischof1 on contraction of igneous rocks in cooling1 #gf ,blue ,gate flexure1 #ac ,sandstone1 #d ,shale1 #d ,bonneville1 ,outlet of ,lake1 #acd ,bowl ,creek arch1 #de ,caons of the ,colorado as obstructions to travel1 #a1 #aea as evidence of arid climate1 #abj ,carboniferous strata1 #h ,carriso ,mountains1 #fi1 #aeb ,circle ,cliffs1 #ad ,cleavage1 ,slaty1 not found1 #ff 1 ,vertical1 produced by sapping1 #ee ,cliffs1 ,circle1 #ad ,climate1 ,arid1 favorable to geological examination1 #b1 #ih 1 ,general influence of1 on erosion1 #ajc 1 ,influence of1 on sculpture1 #aag ,coal1 #e1 #aea ,colorado ,basin1 ,history of the1 #hd ,desert1 #acd ,river1 ,origin of the1 #he ,colors of sandstones1 ,local variation of1 #g ,comminution of detritus aids transportation1 #ajf ,competence1 #aaj ,conditions of rock flexure1 #hc ,cones1 ,alluvial1 #acc ,consequent drainage1 #adc ,contact phenomena1 #fe ,contraction of igneous rocks by cooling1 #ge1 #hj ,corrasion1 #ajj1 #aja 1 ,relation of1 to declivity1 #aab 1 to friction of flow1 #aji 1 to transportation1 #aaa ,cover of the laccolites1 ,depth of the1 #hf1 #id ,crescent arch1 #dd ,cotta1 ,prof4 ,bernhard von1 cited1 #ge ,cretaceous period1 ,disturbance at the close of the1 #aj1 #he rock series1 #d ,cross-lamination1 ,inclination of1 #g ,dana arch1 #dc ,declivity1 ,general influence of1 upon erosion1 #ajb of stream beds1 relation to corrasion1 #aab 1 relation to transportation1 #ajh 1 ,relation of1 to quantity of water1 #aac ,declivities1 ,influence of unequal1 on divides1 #adj ,degradation 7see ,erosion71 #ii1 #aae ,delesse on contraction of igneous rocks in cooling1 #gf ,densities of igneous rocks1 #ge of sedimentary rocks1 #gg ,density a condition of laccolitic intrusion1 #gc1 #gd of porphyritic trachyte1 #gg ,denudation 7see ,erosion71 #ii1 #aae of laccolites1 #ba ,deposition by running water1 #aaa ,diameters of laccolites1 #ib ,dike near ,mount ,ellsworth1 #ei ,dikes and sheets defined1 #bj 1 ,flat-topped1 #bh of ,mount ,ellsworth1 #bc of ,mount ,holmes1 #bh 1 ,relation of1 to strains1 #if ,dinah ,creek ,pass1 #c ,dirty ,devil ,river1 ,flood-plains of1 #aca ,distances1 ,table of1 #ag ,distribution of laccolites1 ,horizontal1 #bj1 #cj 1 ,vertical1 #ba1 #ef ,divides in bad-lands1 ,rounding of1 #abb 1 ,instability of1 #aci 1 ,law of1 #aaf 1 ,stability of1 #ach ,drainage lines1 ,instability of1 #abe 1 ,stability of1 #abd 1 ,systems of1 #abd1 #adc ,dutton1 ,capt4 ,c4 ,e41 on the intrusive rocks1 #fa ,economic geology1 #aea ,elk ,mountains1 #fi ,ellen ,mount 7see ,mount ,ellen74 ,ellsworth ,mount 7see ,mount ,ellsworth74 ,energy of muddy streams1 #ajh streams1 how measured1 #ajf ,equal action1 ,principle of1 #abc ,erosion1 ,conditions which control1 #ajb 1 ,influence of climate upon1 #ajc 1 ,influence of declivity upon1 #ajb ,erosion1 ,influence of rock texture upon1 #ajc 1 ,influence of vegetation upon1 #ajd of ,mount ,ellsworth1 #be 1 ,principles of1 #ii 1 ,processes of1 #ii ,farming lands1 #aeb ,faults on ,mount ,ellsworth1 #bc ,mount ,holmes1 #bh 1 ,region of1 #ab1 #ae ,fish ,lake ,valley1 ,structure of1 #ad ,fissure veins limited in depth1 #hb not found in the ,henry ,mountains1 #hc1 #aea ,flaming ,gorge ,group1 #f ,flat-topped dikes1 #bh ,flexure of rocks1 ,conditions of1 #hc ,flood-plain defined1 #abg ,flow of streams1 ,friction of1 #ajg1 #aji ,folds1 ,the ,great1 #aj1 #aa1 #he ,forces which produce laccolitic arches1 #hg ,form of laccolites1 #ee ,frost1 #ajd ,friction of flow of streams1 #ajg1 #aji ,geikie laccolite1 #da ,gold and silver1 #aea ,granite1 ,eruptive1 #gj ,graves1 ,mr4 ,walter ,h41 #a ,gray ,cliff ,group1 #f ,grazing lands1 #aeb ,heights1 #c1 #aag ,henry1 ,prof4 ,joseph1 #a ,henry ,mountains1 ,altitudes of the1 #b1 #aag caused by resistance of trachyte to erosion1 #be1 #ce 1 ,contributions of the1 to the principles of erosion1 #ii 1 ,detailed description of the1 #bb 1 ,drainage of the1 #add 1 ,economic value of the1 #aeb 1 ,planation in the1 #abg1 #adi 1 ,relation of vegetation to type of sculpture in the1 #aah 1 ,route of travel to the1 #ad2 their structure laccolitic1 #ai1 #ec ,henry's ,fork ,group1 #d ,hillers1 ,mount 7see ,mount ,hillers74 ,hills of planation1 #acj ,historical note1 #ff ,history of the ,colorado ,basin1 #hd ,holmes1 ,mount 7see ,mount ,holmes74 ,holmes1 ,mr4 ,w4 ,h41 on the ,elk ,mountains1 #gj ,la ,lata and ,carriso ,mountains1 #fi ,hopkins on the power of currents1 #ajf ,howell laccolite1 #cd 1 ,mr4 ,edwin ,e41 ,fossils discovered by1 #e2 observation of the ,henry ,mountains1 #ff2 observation of the ,navajo ,mountain1 #fi ,hydrostatic equilibrium1 ,law of1 #gb ,igneous mountains of the ,plateau ,province1 #fg ,igneous rocks1 ,contraction of1 by cooling1 #ge1 #hj ,inconsequent drainage1 #adc ,instability of divides1 #aci drainage lines1 #abe ,interdependence of drainage slopes1 #abc1 #ada ,internal structure of laccolites1 #ee ,intrusive rocks of the ,henry ,mountains1 #ei1 #fa ,isolation of the ,henry ,mountains1 #b1 #ah ,jerry ,butte1 #cd ,jukes ,butte1 #df ,jukes1 ,prof4 ,j4 ,beete1 on prismatic structure1 #gf ,jura-,trias rock series1 #e ,kaibab structure1 #aa ,laccolite ,a1 #cb ,b1 #cb ,c1 #cb ,d1 #ce ,e1 #da ,f1 #db 1 ,geikie1 #da ,h1 #df 1 ,hillers1 #cj 1 ,history of the1 #ie 1 ,howell1 #cd 1 ,jukes1 #df 1 ,marvine1 #db 1 ,newberry1 #da of ,mount ,ellsworth1 #bg of ,mount ,pennell1 #cf of the western base of ,mount ,ellen1 #dj 1 ,peale1 #dg 1 ,possible analogues of the1 #ih 1 ,scrope1 #dg 1 ,sentinel1 #ch 1 ,shoulder1 #db 1 ,steward1 #cb 1 ,the1 defined1 #ai ,laccolites1 ,age of the1 discussed1 #hd 1 ,composite1 #ee 1 ,denudation of1 #ba 1 ,depth of cover of1 #hf1 #id 1 ,detailed description of1 #bb 1 ,diameters of1 #ib 1 ,form of1 #ee1 #ia 1 ,holmes1 #bg 1 ,horizontal1 distribution of1 #bj intruded in soft beds1 #eh 1 ,limital area of1 #ij1 #ig thickness of1 #ia 1 ,material of1 #ei not prismatic1 #ee of the ,elk ,mountains1 #gj of other regions1 #ig2 size limited1 #hf subsequent to the strata which inclose them1 #ea 1 ,vertical distribution of1 #ba1 #ef1 #fe ,laccolitic mountains of the ,plateau ,province1 #fg1 #fi structure characteristic of the ,henry ,mountains1 #ai1 #ec ,sierra ,la ,sal1 etc41 #fi conditioned by densities1 #gd correlated with acidic lavas1 #ga 1 ,discussion of the origin of1 #gb ,lake ,bonneville1 ,outlet of1 #acd 1 ,great ,salt1 ,outlet of1 #acd ,winipeg1 ,origin of1 #abf ,land1 ,agricultural1 #aeb 1 ,grazing1 #aeb sculpture1 ,principles of1 #ii1 #aae 1 ,timber1 #aeb ,la ,lata ,mountains1 #fh1 #fi1 #aeb ,la ,sal ,mountains1 #fh1 #fi1 #aeb ,law of divides1 #aaf 1 ,exception to the1 #abb ,lewis ,creek plain1 #abh ,limital area of laccolites1 #ij1 #ig thickness of laccolites1 #ia ,load1 ,relation of1 to comminution1 #ajg ,mallet1 ,robert1 ,c4 ,e41 on contraction of igneous rocks in cooling1 #gf ,marvine laccolite1 #db ,ma-suk' ,plateau1 #ac ,sandstone1 #d ,shale1 #d ,maze arch1 #dd ,metamorphism in the ,henry ,mountains1 #fe on ,mount ,ellen1 #ch ,ellsworth1 #bd ,hillers1 #ca ,holmes1 #bh ,minerals of the ,henry ,mountains1 #fa1 #fd ,monoclinal shifting1 #ace1 #adj ,mount ,ellen1 ,character of sculpture of1 #aah 1 ,drainage of1 #adh 1 ,structure of1 #ch 1 ,topography of1 #c 1 ,vegetation of1 #aah ,ellsworth1 ,character of sculpture of1 #be1 #aah 1 ,drainage of1 #ade 1 ,stereogram of1 #bc1 #ie 1 ,structure of1 #bb 1 ,topography of1 #c 1 ,vegetation of1 #aah ,hillers1 ,character of sculpture of1 #aai 1 ,drainage of1 #adg 1 ,structure of1 #cj 1 ,topography of1 #c 1 ,vegetation of1 #aah ,holmes1 ,character of sculpture of1 #aah 1 ,drainage of1 #adf 1 ,structure of1 #bg 1 ,topography of1 #c ,mount ,holmes1 ,vegetation of1 #aah ,pennell1 ,character of sculpture of1 #aai 1 ,drainage of1 #adh 1 ,structure of1 #ce 1 ,topography of1 #c 1 ,vegetation of1 #aah ,mount ,taylor1 #ga ,mud-cracks1 ,fossil1 #i ,navajo ,mountain1 #fi1 #aeb ,newberry1 ,dr4 ,j4 ,s41 on the ,sierra ,abajo1 #fg ,la ,sal1 #fh laccolite1 #da ,oblique lamination1 ,inclination of1 #g ,peale1 ,dr4 ,a4 ,c41 on igneous mountains of ,colorado1 #fi on the ,elk ,mountains1 #gj ,peale laccolite1 #dg ,pennell1 ,mount 7see ,mount ,pennell74 ,pennellen ,pass1 #c ,pine ,alcove ,creek1 ,former course of1 #acj ,planation1 #abf1 #aci 1 ,hills of1 #acj ,plasticity of solids1 #hb1 #hc1 #ig ,plateaus enumerated1 #ac ,precipitation from running water1 #aaa ,pressure a condition for rock flexure1 #ha1 #hc1 #if ,prismatic structure1 ,absence of1 #ee1 #gf defined1 #ee ,ponding1 #abe1 #aci ,porphyritic trachyte1 #fj1 #fd ,porphyry2 use of term discussed1 #fc ,powell1 ,prof4 ,j4 ,w41 on the climate of the ,colorado ,basin1 #abj ,pulpit arch1 #cc1 #adg ,rankine on flexure of beams1 #ij ,red ,gate flexure1 #ac 1 ,flood-plains of1 #aca 1 ,the1 #af ,revet-crags defined1 #be of ,mount ,hillers1 #ca of ,mount ,holmes1 #bi of ,mount ,pennell1 #cg ,ripple-marks1 ,fossil1 #af ,river terraces produced by planation1 #acb ,rivers1 ,ancient1 no greater than modern1 #acc ,rock texture1 ,influence of1 on sculpture1 #aae1 #ace1 #adj 1 ,general influence of1 on erosion1 #ajc ,rocks of the ,henry ,mountains1 ,intrusive1 #ei1 #fa 1 ,sedimentary1 #c ,rotation of the earth1 #adb ,route to the ,henry ,mountains1 #ad ,san ,rafael fold1 #af1 #ah ,scrope laccolite1 #dg ,sculpture1 ,alpine1 #cf1 #ch influenced by climate1 #aag distribution of divides1 #aaf rock structure1 #aae1 #ace1 #adj ,sculpture of bad-lands1 #abj of ,mount ,ellsworth1 #be 1 ,principles of1 #ii1 #aae ,sentinel ,butte1 #ch ,sheets and dikes defined1 #bj of ,mount ,ellsworth1 #bd of ,mount ,holmes1 #bh 1 ,relation of1 to strains1 #if ,shin-ar'-ump ,group1 #f ,shoulder laccolite1 #db ,sierra ,abajo1 #fg1 #fi1 #aeb ,carriso1 #gi1 #aeb ,la ,lata1 #fh1 #fi1 #aeb ,la ,sal1 #fh1 #fi1 #aeb ,solidity of rocks not absolute1 #hb1 #hc1 #ig ,specific gravities 7see ,densities74 ,specimens of ,henry ,mountain trachyte1 #fj ,springs2 relation to soft strata explained1 #hb ,stability of divides1 #ach of drainage lines1 #abd ,stereogram1 how made1 #aa1 #di of ,mount ,ellsworth1 #bc1 #ie of the ,henry ,mountains1 #di and ,waterpocket flexure1 #aa ,steward laccolite1 #cb 1 ,mr4 ,john ,f41 cited1 #ff ,strains shown by dikes and sheets1 #if ,stretching of strata1 #hj ,structure1 ,law of1 #aae ,suncracks1 ,fossil1 #i ,superimposed drainage1 #add ,systems of drainage1 #abd1 #adc ,table of altitudes1 #aag densities of sedimentary rocks1 #gh in order of superposition1 #gi trachytes1 #gg diameters of laccolites1 #ib distances1 #ag mean densities of certain rock series1 #hj ,tantalus ,creek1 #ag 1 ,flood-plains of1 #aca ,taylor1 ,mount1 #ga ,temple ,creek1 #af 1 ,flood-plains of1 #aca ,terraces1 ,river1 produced by planation1 #acb ,tertiary strata protected by lava1 #ab ,thicknesses of individual strata1 #g ,thompson1 ,prof4 ,a4 ,h41 #a1 #ff ,thousand ,lake ,mountain1 ,view from1 #ae ,timber land1 #aeb ,trachyte1 ,porphyritic1 #fj1 #fd ,trachytes of the ,henry ,mountains not vesicular1 #ea1 #fd ,transportation1 #ajj1 #aja by streams1 analyzed1 #ajf ,conditions which determine rate of1 #aaj favored by comminution of material1 #ajf declivity1 #ajh quantity of water1 #aji 1 ,relation of1 to corrasion1 #aaa ,trend1 ,absence of1 #b1 #cj1 #ih ,tu-nunk' ,sandstone1 #d ,shale1 #d ,unconformities1 #h1 #he ,unconformity at ,salina1 #ad ,vegetation1 ,general influence of1 on erosion1 #ajd ,veins1 ,absence of fissure1 #hc1 #aea 1 ,fissure1 limited in depth1 #hb ,vermilion ,cliff ,group1 #f ,vertical cleavage by sapping1 #ee ,volcanoes of the ,plateau ,province1 ,extinct1 #fg1 #gj ,volume of streams1 ,influence of1 on erosion1 #ajd transportation1 #aji 1 ,relation of1 to declivity1 #aac ,warren1 ,general ,g4 ,k41 on the valley of the ,minnesota ,river1 #abf ,waterpocket ,caon1 #acg flexure1 described1 #ab 1 ,passes across the1 #af ,watersheds 7see ,divides74 ,weathering1 #ajj ,white1 ,dr4 ,c4 ,a42 identification of ,henry's ,fork ,group1 #d ,whitney1 ,prof ,j4 ,d41 on inclination of bedding1 #eb ,winipeg1 ,origin of ,lake1 #abf ,zones of laccolites1 #eg1 #eh1 #gd ,illustration3 ,plate ,i4 ,,map of the ,,henry ,,mountains ,,and ,,vicinity4 ,photographed from a model in relief4 ,triangulation by ,a4 ,h4 ,thompson4 ,topography by ,w4 ,h4 ,graves4 ,illustration3 ,plate ,,ii4 ,,stereogram of the ,,henry ,,mountains ,,and ,,waterpocket ,,fold4 ,including the same area as ,plate ,i4 ,illustration3 ,plate ,,iii4 ,,map of the ,,henry ,,mountains4 by ,g4 ,k4 ,gilbert4 ,photographed from a model in relief4 ,illustration3 ,plate ,,iv4 ,,stereogram of the ,,displacements of the ,,henry ,,mountains including the same area as ,plate ,,iii4 ,the ,blue ,gate ,sandstone is restored so as to exhibit the form it received by the uplift of the laccolitic domes4 ,illustration3 ,plate ,v4 ,,map of the ,,henry ,,mountains by ,g4,k4 ,gilbert4 ,from a model in relief4 ---------------------------------------- -------------------------------- ,,transcriber',s ,,notes ,page ,changed from ,changed to #cj degradation1 less than one-half degradation1 less than one-half has been stripped of its cover has been stripped of its cover of arch-arching of overarching ,typos fixed2 non-standard spelling and dialect retained4 ,used numbers for footnotes4 ,enclosed italics font in underscores4 ,the caret 77 serves as a superscript indicator1 applicable to individual characters 7like #b;d7 and even entire phrases 7like #ast74 ,subscripts are shown using an underscore 77 with curly braces 1 as in ,h#b,o4