,wisconsin ,geological and ,natural ,history ,survey4 ,e4 ,a4 ,,birge1 ,director4 ,c4 ,r4 ,,van ,,hise1 ,consulting ,geologist4 ,,bulletin ,,no4 ,v4 ,,educational ,,series ,,no4 #a4 ,,the ,,geography ,,of ,,the ,,region ,,about ,,devil',s ,,lake ,,and ,,the ,,dalles ,,of ,,the ,,wisconsin1 ,with ,some ,notes on ,its ,surface ,geology4 ,,by ,,rollin ,d4 ,,salisbury1 ,a4 ,m41 ,professor of ,geographic ,geology1 ,university of ,chicago1 ,,and ,,wallace ,w4 ,,atwood1 ,b4 ,s41 ,assistant in ,geology1 ,university of ,chicago4 ,,madison1 ,,wis4 ,published by the ,state4 #aijj4 ,wisconsin ,geological and ,natural ,history ,survey4 ---------------------------------------- --------------------------- ,,board ,,of ,,commissioners4 ,,edward ,,scofield1 ,governor of the ,state4 ,l4 ,d4 ,,harvey1 ,state ,superintendent of ,public ,instruction4 ,,charles ,k4 ,,adams1 ,president1 ,president of the ,university of ,wisconsin4 ,,edwin ,e4 ,,bryant1 ,vice-,president1 ,president of the ,commissioners of ,fisheries4 ,,charles ,s4 ,,slichter1 ,secretary1 ,president of the ,wisconsin ,academy of ,sciences1 ,arts1 and ,letters4 ---------------------------------------- ---------------------- ,e4 ,a4 ,,birge1 ,director of the ,survey4 ,c4 ,r4 ,,van ,,hise1 ,consulting ,geologist4 ,e4 ,r4 ,,buckley1 ,assistant ,geologist4 ,in charge of ,economic ,geology4 ,s4 ,,weidman1 ,assistant ,geologist4 ,in charge of ,geology of ,wausau ,district4 ,l4 ,s4 ,,smith1 in charge of ,hydrography4 ,s4 ,v4 ,,peppel1 ,chemist4 ,f4 ,r4 ,,denniston1 ,artist4 ,illustration3 ,,the ,,dalles ,,of ,,the ,,wisconsin4 ,,contents4 ---------------------------------------- ----------------- ,,part ,i4 ,,the ,,topography ,,with ,,some ,,notes ,,on ,,the ,,surface ,,geology4 ,,chapter ,i4 ,,general ,,geographic ,,features ,i4 ,the ,plain ,surrounding the ,quartzite ,ridges4 ,topography ,structure ,origin of the ,sandstone and ,limestone ,origin of the ,topography ,,ii4 ,the ,quartzite ,ridges ,topography ,the ,structure and ,constitution of the ,ridges ,,iii4 ,relations of the ,sandstone of the ,plain to the ,quartzite of the ,ridges ,,part ,,ii4 ,,history ,,of ,,the ,,topography4 ,,chapter ,,ii4 ,,outline ,,of ,,the ,,history ,,of ,,the ,,rock ,,formations ,,which ,,show ,,themselves ,,at ,,the ,,surface4 ,i4 ,the ,pre-,cambrian ,history of the ,quartzite ,from loose ,sand to ,quartzite ,uplift and ,deformation4 ,dynamic ,metamorphism ,erosion of the ,quartzite ,thickness of the ,quartzite ,,ii4 ,the ,history of the ,paleozoic ,strata ,the ,subsidence ,the ,potsdam ,sandstone 7and ,conglomerate7 ,the ,lower ,magnesian ,limestone ,the ,st4 ,peters ,sandstone ,younger ,beds ,climatic ,conditions ,time involved ,the ,uplift ,,chapter ,,iii4 ,,general ,,outline ,,of ,,rain ,,and ,,river ,,erosion ,elements of ,erosion ,weathering ,corrasion ,erosion without ,valleys ,the ,beginning of a ,valley ,the ,course of a ,valley ,tributary ,valleys ,how a ,valley gets a ,stream ,limits of a ,valley ,a ,cycle of ,erosion ,effects of unequal ,hardness ,falls and ,rapids ,narrows ,erosion of folded ,strata ,base-level ,plains and ,peneplains ,transportation and ,deposition ,topographic ,forms resulting from ,stream ,deposition ,rejuvenation of ,streams ,underground ,water ,,chapter ,,iv4 ,,erosion ,,and ,,the ,,development ,,of ,,striking ,,scenic ,,features ,establishment of ,drainage ,striking scenic ,features ,the ,baraboo ,bluffs ,the ,narrows in the ,quartzite ,glens ,natural ,bridge ,the ,dalles of the ,wisconsin ,the ,mounds and ,castle ,rocks ,,chapter ,v4 ,,the ,,glacial ,,period4 ,the ,drift ,snow ,fields and ice ,sheets ,the ,north ,american ice ,sheets ,the ,work of glacier ,ice ,erosive ,work of ,ice4 ,effect on ,topography ,deposition by the ,ice4 ,effect on ,topography ,direction of ice ,movement ,effect of ,topography on ,movement ,glacial ,deposits ,the ground ,moraine ,constitution ,topography ,terminal ,moraines ,topography of terminal ,moraines ,the terminal ,moraine about ,devil's ,lake ,the ,moraine on the main ,quartzite ,range ,constitution of the marginal ,ridge ,the ,slope of the upper ,surface of the ,ice at the ,margin ,stratified ,drift ,its ,origin ,glacial ,drainage ,stages in the ,history of an ,ice ,sheet ,deposits made by extraglacial ,waters during the maximum ,extension of the ,ice ,at the ,edge of the ,ice1 on ,land ,beyond the ,edge of the ,ice1 on ,land ,deposits at and beyond the ,edge of the ,ice in standing ,water ,deposits made by extraglacial ,waters during the ,retreat of the ,ice ,deposits made by extraglacial ,waters during the ,advance of the ,ice ,deposits made by subglacial ,streams ,relations of stratified to unstratified ,drift ,complexity of ,relations ,classification of stratified ,drift on the ,basis of ,position ,extraglacial ,deposits ,supermorainic deposits ,the submorainic 7basal7 ,deposits ,intermorainic stratified ,drift ,changes in ,drainage effected by the ,ice ,while the ,ice was on ,wisconsin ,lake ,baraboo ,lake ,devil's ,lake in glacial ,times ,after the ,ice had disappeared ,lakes ,existing ,lakes ,changes in ,streams ,skillett ,creek ,the ,wisconsin ,the ,driftless ,area ,contrast between glaciated and unglaciated ,areas ,topography ,drainage ,mantle ,rock ,,list ,,of ,,illustrations4 ---------------------------------------- -------------------- ,,plates4 ,plate ,frontispiece4 ,the ,dalles of the ,wisconsin ,i4 ,general map of the ,devil's ,lake region ,,ii4 ,local map of the ,devil's ,lake region ,,iii4 ,fig4 #a--,ripple marks on a slab of sandstone ,fig4 #b--,piece of ,potsdam conglomerate ,,iv4 ,lower ,narrows of the ,baraboo ,v4 ,devil's ,lake notch ,,vi4 ,east bluff of ,devil's ,lake ,,vii4 ,east bluff at the ,upper ,narrows of the ,baraboo near ,ableman's ,,viii4 ,vertical shear zone face of east bluff at ,devil's ,lake ,,ix4 ,massive quartzite in situ in road through ,upper ,narrows near ,ableman's ,x4 ,brecciated quartzite ,,xi4 ,northwest wall of the ,upper ,narrows ,,xii4 ,steamboat ,rock ,,xiii4 ,fig4 #a--;,a very young valley ,fig4 #b--;,a valley at later stage of development ,fig4 #c--,young valleys ,,xiv4 ,fig4 #a--,same valleys as shown in ,pl4 ,,xiii1 ,fig4 #c1 but at a later stage of development ,fig4 #b--,same valleys as shown in ,fig4 #a in later stage of development ,,xv4 ,diagram illustrating how a hard inclined layer of rock becomes a ridge in the process of degradation ,,xvi4 ,skillett ,falls ,,xvii4 ,a group of mounds on the plain northwest from ,camp ,douglas ,,xviii4 ,castle ,rock near ,camp ,douglas ,,xix4 ,fig4 #a--,sketch of a young valley ,fig4 #b--,same valleys as shown in ,fig4 #a in later stage of development ,,xx4 ,fig4 #a--,sketch of a part of a valley at a stage of development corresponding to the cross section shown in ,figure #ba ,fig4 #b--,sketch of a section of the ,baraboo valley ,,xxi4 ,cleopatra's ,needle ,,xxii4 ,turk's ,head ,,xxiii4 ,devil's ,doorway ,,xxiv4 ,talus slope on east bluff of ,devil's ,lake ,,xxv4 ,dorward's ,glen ,,xxvi4 ,natural ,bridge near ,denzer ,,xxvii4 ,the ,navy ,yard ,,xxviii4 ,chimney ,rock ,,xxix4 ,an island in the ,lower ,dalles ,,xxx4 ,view in ,lower ,dalles ,,xxxi4 ,stand ,rock ,,xxxii4 ,petenwell ,peak ,,xxxiii4 ,north ,american ice sheet ,,xxxiv4 ,owl's ,head ,,xxxv4 ,cut in glacial drift ,,xxxvi4 ,glaciated stones ,,xxxvii4 ,topographic map of a small area about ,devil's ,lake ,,xxxviii4 ,distorted laminae of silt and clay ,,figures ,,in ,,text4 ,figure #a4 ,profile across the ,baraboo quartzite ranges through ,baraboo #b4 ,profile across the ,baraboo ranges through ,merrimac ,transcriber's note3 ,there is no figure #c4 #d4 ,diagram showing the structure of the quartzite #e4 ,diagram showing the relation of the ,potsdam sandstone to the ,baraboo quartzite #f4 ,diagram illustrating effect of faulting on outcrop #g4 ,diagram showing the disposition of sediments about an island #h4 ,the same as #g after subsidence #i4 ,diagram showing relation of ,potsdam conglomerate to quartzite at ,devil's ,lake #aj4 ,cross section of a delta #aa4 ,the geological formations of southern ,wisconsin #ab4 ,a typical river system #ac4 ,diagram illustrating the relations of ground water to streams #ad4 ,diagram illustrating the shifting of divides #ae4 ,diagram showing topography at the various stages of an erosion cycle #af4 ,diagram illustrating the development of rapids and falls #ag4 ,sketch looking northwest from ,camp ,douglas #ah4 ,diagrammatic cross section of a young valley #ai4 ,diagrammatic profile of a young valley #bj4 ,diagrammatic cross section of a valley in a later stage of development #ba4 ,the same at a still later stage #bb4 ,diagram illustrating the topographic effect or rejuvenation of a stream by uplift #bc4 ,normal profile of a valley bottom #bd4 ,profile of a stream rejuvenated by uplift #be4 ,diagram illustrating monoclinal shifting #bf4 ,diagram showing the relation of the ,potsdam sandstone to the quartzite at the ,upper ,narrows #bg4 ,diagrammatic cross section of a field of ice and snow #bh4 ,shape of an erosion hill before glaciation #bi4 ,the same after glaciation #cj4 ,diagram showing the effect of a valley on the movement of ice #ca4 ,the same under different conditions #cb4 ,diagram showing the relation of drift to the underlying rock where the drift is thick #cc4 ,the same where the drift is relatively thin #cd4 ,diagrammatic representation of the effect of a hill on the edge of the ice #ce4 ,the same at a later stage of the ice advance #cf4 ,map showing the relation of the ice lobes during the ,wisconsin epoch of the glacial period #cg4 ,sketch of the terminal moraine topography east of ,devil's ,lake #ch4 ,cut through the terminal moraine east of ,kirkland #ci4 ,cross section of the marginal ridge of the moraine on the south slope of the ,devil's nose #dj4 ,cross section of the marginal ridge of the moraine on the crest of the quartzite range #da4 ,morainic outwash plain #db4 ,the same in other relations #dc4 ,skillett ,creek and its peculiarities #dd4 ,the ,wisconsin valley near ,kilbourn city #de4 ,drainage in the driftless area #df4 ,drainage in the glaciated area #dg4 ,section in the driftless region showing relation of the soil to the solid rock beneath ,,part ,i4 ---------------------------------------- -------------------- ,,the ,,topography4 ,,with ,,some ,,notes ,,on ,,the ,,surface ,,geology4 ,,geography ,,and ,,surface ,,geology ,,of ,,the ,,devil',s ,,lake ,,region4 ,,chapter ,i4 ,,general ,,geographic ,,features4 ,this report has to do with the physical geography of the area in south central ,wisconsin1 shown on the accompanying sketch map1 ,plate ,i4 ,the region is of especial interest1 both because of its striking scenery1 and because it illustrates clearly many of the principles involved in the evolution of the geography of land surfaces4 ,generally speaking1 the region is an undulating plain1 above which rise a few notable elevations1 chief among which are the ,baraboo quartzite ranges1 marked by diagonal lines on ,plates ,i and ,,ii4 ,these elevations have often been described as two ranges4 ,the ,south or main range lies three miles south of ,baraboo1 while the ,north or lesser range1 which is far from continuous1 lies just north of the city4 ,the main range has a general east-west trend1 and rises with bold and sometimes precipitous slopes #ejj to #hjj feet above its surroundings4 ,a deep gap three or four miles south of ,baraboo 7,plates ,,ii1 ,v1 and ,,xxxvii7 divides the main range into an eastern and a western portion1 known respectively as the ,east and ,west bluffs or ranges4 ,in the bottom of the gap lies ,devil's lake 7i1 ,plate ,,ii and ,plate ,,xxxvii71 perhaps the most striking body of water of its size in the state1 if not in the whole northern interior4 ,a general notion of the topography of a small area in the immediate vicinity of the lake may be obtained from ,plate ,,xxxvii4 ,the highest point in the range is about four miles east of the lake1 and has an elevation of more than #a1fjj feet above sea level1 more than #a1jjj feet above ,lake ,michigan1 and about #hjj feet above the ,baraboo valley at its northern base4 ,the eastward extension of the west range 7,plate ,,xxxvii7 lying south of the lake1 and popularly known as the ,devil's nose1 reaches an elevation of a little more than #a1ejj feet4 ,the lesser or ,north quartzite range 7,plate ,,ii7 rises #cjj feet to #ejj feet above its surroundings4 ,it assumes considerable prominence at the ,upper and ,lower narrows of the ,baraboo 7b and c1 ,plate ,,ii1 c1 ,plate ,,xxxvii and ,plate ,,iv74 ,the ,north range is not only lower than the ,south range1 but its slopes are generally less steep1 and1 as ,plate ,,ii shows1 it is also less continuous4 ,the lesser elevation and the gentler slopes make it far less conspicuous4 ,about three miles southwest of ,portage 7,plate ,,ii7 the ,north and ,south ranges join1 and the elevation at the point of union is about #dej feet above the ,wisconsin river a few miles to the east4 ,the lower country above which these conspicuous ridges rise1 has an average elevation of about #a1jjj feet above the sea1 and extends far beyond the borders of the area with which this report is concerned4 ,the rock underlying it in the vicinity of ,baraboo is chiefly sandstone1 but there is much limestone farther east and south1 in the area with which the ,baraboo region is topographically continuous4 ,both the sandstone and limestone are much less resistant than the quartzite1 and this difference has had much to do with the topography of the region4 ,the distinctness of the quartzite ridges as topographic features is indicated in ,plate ,,xxxvii by the closeness of the contour lines on their slopes4 ,the same features are shown in ,figs4 #a and #b1 which represent profiles along two north-south lines passing through ,baraboo and ,merrimac respectively4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,i4 ,general map showing the location of the chief points mentioned in this report4 ,the location of the area shown in ,plate ,,xxxvii1 centering about ,baraboo1 is indicated4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,ii4 ,map of ,area considered in this ,report4 ,illustration3 ,fig4 #a4--,profile along a line extending due north and south from ,baraboo across the north and south ranges4 ,the dotted continuation northward1 represents the extension of the profile beyond the topographic map1 ,plate ,,xxxvii4 ,illustration3 ,fig4 #b4--,profile north from ,merrimac across the quartzite ranges4 ,the dotted continuation northward represents the extension of the profile beyond the topographic map1 ,plate ,,xxxvii4 ,i4 ,,the ,,plain ,,surrounding ,,the ,,quartzite ,,ridges4 ,topography4--,as seen from the top of the quartzite ridges1 the surrounding country appears to be an extensive plain1 but at closer range it is seen to have considerable relief although there are extensive areas where the surface is nearly flat4 ,the relief of the surface is of two somewhat different types4 ,in some parts of the area1 especially in the western part of the tract shown on ,plate ,,ii1 the surface is made up of a succession of ridges and valleys4 ,the ridges may be broken by depressions at frequent intervals1 but the valleys are nowhere similarly interrupted4 ,it would rarely be possible to walk along a ridge or divide for many miles without descending into valleys2 but once in a valley in any part of the area1 it may be descended without interruption1 until the ,baraboo1 the ,wisconsin1 the ,mississippi1 and finally the gulf is reached4 ,in other words1 the depressions are continuous1 but the elevations are not4 ,this is the first type of topography4 ,where this type of topography prevails its relation to drainage is evident at a glance4 ,all the larger depressions are occupied by streams continuously1 while the smaller ones contain running water during some part of the year4 ,the relations of streams to the depressions1 and the wear which the streams effect1 whether they be permanent or temporary1 suggest that running water is at least one of the agencies concerned in the making of valleys4 ,an idea of the general arrangement of the valleys1 as well as many suggestions concerning the evolution of the topography of the broken plain in which they lie might be gained by entering a valley at its head1 and following it wherever it leads4 ,at its head1 the valley is relatively narrow1 and its slopes descend promptly from either side in such a manner that a cross-section of the valley is ,v-shaped4 ,in places1 as west of ,camp ,douglas1 the deep1 steep-sided valleys are found to lead down and out from a tract of land so slightly rolling as to be well adapted to cultivation4 ,following down the valley1 its progressive increase in width and depth is at once evident1 and at the same time small tributary valleys come in from right and left4 ,at no great distance from the heads of the valleys1 streams are found in their bottoms4 ,as the valleys increase in width and depth1 and as the tributaries become more numerous and wider1 the topography of which the valleys are a feature1 becomes more and more broken4 ,at first the tracts between the streams are in the form of ridges1 wide if parallel valleys are distant from one another1 and narrow if they are near4 ,the ridges wind with the valleys which separate them4 ,whatever the width of the inter-stream ridges1 it is clear that they must become narrower as the valleys between them become wider1 and in following down a valley a point is reached1 sooner or later1 where the valleys1 main and tributary1 are of such size and so numerous that their slopes constitute a large part of the surface4 ,where this is true1 and where the valleys are deep1 the land is of little industrial value except for timber and grazing4 ,when1 in descending a valley system1 this sort of topography is reached1 the roads often follow either the valleys or the ridges1 however indirect and crooked they may be4 ,where the ridges separating the valleys in such a region have considerable length1 they are sometimes spoken of as hog backs4 ,still farther down the valley system1 tributary valleys of the second and lower orders cross the hog backs1 cutting them into hills4 ,by the time this sort of topography is reached1 a series of flats is found bordering the streams4 ,these flats may occur on both sides of the stream1 or on but one4 ,the topography and the soil of these flats are such as to encourage agriculture1 and the river flats or alluvial plains are among the choicest farming lands4 ,with increasing distance from the heads of the valleys1 these river plains are expanded1 and may be widened so as to occupy the greater part of the surface4 ,the intervening elevations are there relatively few and small4 ,their crests1 however1 often rise to the same level as that of the broader inter-stream areas farther up the valleys4 ,the relations of the valleys and the high lands separating them1 is such as to suggest that there are1 generally speaking1 two sets of flat surfaces1 the higher one representing the upland in which the valleys lie1 the lower one representing the alluvial plains of the streams4 ,the two sets of flats are at once separated and connected by slopes4 ,at the head of a drainage system1 the upland flats predominate2 in the lower courses1 the river plains2 in an intermediate stage1 the slopes are more conspicuous than either upper or lower flat4 ,southwest from ,devil's lake and northwest from ,sauk ,city1 in the valley of ,honey creek1 and again in the region southwest from ,camp ,douglas1 the topography just described is well illustrated4 ,in both these localities1 as in all others where this type of topography prevails1 the intimate relations of topography and drainage cannot fail to suggest that the streams which are today widening and deepening the valleys through which they flow1 had much to do with their origin and development4 ,this hypothesis1 as applied to the region under consideration1 may be tested by the study of the structure of the plain4 ,the second type of topography affecting the plain about the quartzite ranges is found east of a line running from ,kilbourn ,city to a point just north of ,prairie du ,sac4 ,though in its larger features the area east of this line resembles that to the west1 its minor features are essentially different4 ,here there are many depressions which have no outlets1 and marshes1 ponds1 and small lakes abound4 ,not only this1 but many of the lesser elevations stand in no definite relation to valleys4 ,the two types of topography make it clear that they were developed in different ways4 ,structure4--,examination of the country surrounding the ,baraboo ridges shows that its surface is underlaid at no great depth by horizontal or nearly horizontal beds of sandstone and limestone 7see ,plates ,,xvi1 ,,xxviii1 and ,frontispiece74 ,these beds are frequently exposed on opposite sides of a valley1 and in such positions the beds of one side are found to match those on the other4 ,this is well shown along the narrow valley of ,skillett creek just above the ,pewit's nest4 ,here the swift stream is rapidly deepening its channel1 and it is clear that a few years hence1 layers of sandstone which are now continuous beneath the bed of the creek will have been cut through1 and their edges will appear on opposite sides of the valley just as higher layers do now4 ,here the most skeptical might be convinced that the layers of rock on either side of the narrow gorge were once continuous across it1 and may see1 at the same time1 the means by which the separation was effected4 ,between the slight separation1 here1 where the valley is narrow1 and the great separation where the valleys are wide1 there are all gradations4 ,the study of progressively wider valleys1 commencing with such a gorge as that referred to1 leaves no room for doubt that even the wide valleys1 as well as the narrow ones1 were cut out of the sandstone by running water4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,iii4 ,illustration3 ,,fig4 #a4 ,ripple marks on a slab of ,potsdam sandstone4 ,illustration3 ,,fig4 #b4 ,piece of ,potsdam conglomerate4 ,the larger pebbles are about three inches in diameter4 ,the same conclusion as to the origin of the valleys may be reached in another way4 ,either the beds of rock were formed with their present topography1 or the valleys have been excavated in them since they were formed4 ,their mode of origin will therefore help to decide between these alternatives4 ,origin of the sandstone and limestone4--,the sandstone of the region1 known as the ,potsdam sandstone1 consists of medium sized grains of sand1 cemented together by siliceous1 ferruginous1 or calcareous cement4 ,if the cement were removed1 the sandstone would be reduced to sand1 in all respect similar to that accumulating along the shores of seas and lakes today4 ,the surfaces of the separate layers of sandstone are often distinctly ripple-marked 7,fig4 #a1 ,pl4 ,,iii71 and the character of the markings is identical in all essential respects with the ripples which affect the surface of the sand along the shores of ,devil's lake1 or sandy beaches elsewhere1 at the present time4 ,these ripple marks on the surfaces of the sandstone layers must have originated while the sand was movable1 and therefore before it was cemented into sandstone4 ,in the beds of sandstone1 fossils of marine animals are found4 ,shells1 or casts of shells of various sorts are common1 as are also the tracks and burrowings of animals which had no shells4 ,among these latter signs of life may be mentioned the borings of worms4 ,these borings are not now always hollow1 but their fillings are often so unlike the surrounding rock1 that they are still clearly marked4 ,these worm borings1 like the ripple marks1 show that the sand was once loose4 ,the basal beds of the sandstone are often conglomeratic4 ,the conglomeratic layers are made up of water-worn pieces of quartzite1 ,plate ,,iii1 ,fig4 #b1 ranging in size from small pebbles to large bowlders4 ,the interstices of the coarse material are filled by sand1 and the whole cemented into solid rock4 ,the conglomeratic phase of the sandstone may be seen to advantage at ,parfrey's glen 7a1 ,plate ,,xxxvii7 and ,dorward's glen1 7b1 same plate7 on the ,east bluff of ,devil's lake above the ,cliff ,house1 and at the ,upper narrows of the ,baraboo1 near ,ablemans4 ,it is also visible at numerous other less accessible and less easily designated places4 ,from these several facts1 viz43 the horizontal strata1 the ripple-marks on the surfaces of the layers1 the fossils1 the character of the sand1 and the water-worn pebbles and bowlders of the basal conglomerate1 positive conclusions concerning the origin of the formation may be drawn4 ,the arrangement in definite layers proves that the formation is sedimentary2 that is1 that its materials were accumulated in water whither they had been washed from the land which then existed4 ,the ripple-marks show that the water in which the beds of sand were deposited was shallow1 for in such water only are ripple-marks made4#a ,once developed on the surface of the sand they may be preserved by burial under new deposits1 just as ripple-marks on sandy shores are now being buried and preserved4 #a ,ripple marks are often seen on the surface of wind-blown sand1 but the other features of this sandstone show that this was not its mode of accumulation4 ,the conglomerate beds of the formation corroborate the conclusions to which the composition and structure of the sandstone point4 ,the water-worn shapes of the pebbles and stones show that they were accumulated in water1 while their size shows that the water must have been shallow1 for stones of such sizes are handled only by water of such slight depth that waves or strong currents are effective at the bottom4 ,furthermore1 the large bowlders show that the source of supply 7quartzite7 must have been close at hand1 and that therefore land composed of this rock must have existed not far from the places where the conglomerate is found4 ,the fossils likewise are the fossils of aquatic life4 ,not only this1 but they are the fossils of animals which lived in salt water4 ,the presence of salt water1 that is1 the sea1 in this region when the sand of the sandstone was accumulating1 makes the wide extent of the formation rational4 ,from the constitution and structure of the sandstone1 it is therefore inferred that it accumulated in shallow sea water1 and that1 in the vicinity of ,devil's lake1 there were land masses 7islands7 of quartzite which furnished the pebbles and bowlders found in the conglomerate beds at the base of the formation4 ,this being the origin of the sandstone1 it is clear that the layers which now appear on opposite sides of valleys must once have been continuous across the depressions2 for the sand accumulated in shallow water is never deposited so as to leave valleys between ridges4 ,it is deposited in beds which are continuous over considerable areas4 ,within the area under consideration1 limestone is much less widely distributed than sandstone4 ,thin beds of it alternate with layers of sandstone in the upper portion of the ,potsdam formation1 and more massive beds lie above the sandstone on some of the higher elevations of the plain about the quartzite ridge4 ,this is especially true in the southern and southwestern parts of the region shown on ,plate ,,ii4 ,the limestone immediately overlying the sandstone is the ,lower ,magnesian limestone4 ,the beds of limestone1 like those of the sandstone beneath1 are horizontal or nearly so1 and the upper formation lies conformably on the lower4 ,the limestone does not contain water-worn pebbles1 and the surfaces of its layers are rarely if ever ripple-marked2 yet the arrangement of the rock in distinct layers which carry fossils of marine animals shows that the limestone1 like the sandstone beneath1 was laid down in the sea4 ,the bearing of this origin of the limestone on the development of the present valleys is the same as that of the sandstone4 ,origin of the topography4--,the topography of the plain surrounding the quartzite ridges1 especially that part lying west of ,devil's lake1 is then an erosion topography1 developed by running water4 ,its chief characteristic is that every depression leads to a lower one1 and that the form of the elevations1 hills or ridges1 is determined by the valleys4 ,the valleys were made2 the hills and ridges left4 ,if the material carried away by the streams could be returned1 the valleys would be filled to the level of the ridges which bound them4 ,were this done1 the restored surface would be essentially flat4 ,it is the sculpturing of such a plain1 chiefly by running water1 which has given rise to the present topography4 ,in the development of this topography the more resistant limestone has served as a capping1 tending to preserve the hills and ridges4 ,thus many of the hills1 especially in the southwest portion of the area shown in ,plate ,,ii1 are found to have caps of the ,lower ,magnesian formation4 ,such hills usually have flat tops and steep or even precipitous slopes down to the base of the capping limestone1 while the sandstone below1 weathering more readily1 gives the lower portions of the hills a gentler slope4 ,the elevations of the hills and ridges above the axes of the valleys or1 in other words1 the relief of the plain is1 on the average1 about #cjj feet1 only a few of the more prominent hills exceeding that figure4 ,the topography east of the line between ,kilbourn ,city and ,prairie du ,sac is not of the unmodified erosion type1 as is made evident by marshes1 ponds and lakes4 ,the departure from the erosion type is due to a mantle of glacial drift which masks the topography of the bedded rock beneath4 ,its nature1 and the topographic modifications which it has produced1 will be more fully considered in a later part of this report4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,iv4 ,the ,lower ,narrows of the ,baraboo from a point on the ,south range4 ,,ii4 ,,the ,,quartzite ,,ridges4 ,topography4--,the ,south or main quartzite range1 about #bc miles in length and one to four miles in width1 rises #ejj feet to #hjj feet above the surrounding sandstone plain4 ,its slopes are generally too steep for cultivation1 and are clothed for the most part with a heavy growth of timber1 the banks of forest being broken here and there by cultivated fields1 or by the purple grey of the rock escarpments too steep for trees to gain a foothold4 ,with the possible exception of the ,blue mounds southwest of ,madison1 this quartzite range is the most obtrusive topographic feature of southern ,wisconsin4 ,as approached from the south1 one of the striking features of the range is its nearly even crest4 ,extending for miles in an east-west direction1 its summit gives a sky-line of long and gentle curves1 in which the highest points are but little above the lowest4 ,viewed from the north1 the evenness of the crest is not less distinct1 but from this side it is seen to be interrupted by a notable break or notch at ,devil's lake 7,plates ,v and ,,xxxvii74 ,the pass across the range makes a right-angled turn in crossing the range1 and for this reason is not seen from the south4 ,the ,north or lesser quartzite range lying north of ,baraboo is both narrower and lower than the south range1 and its crest is frequently interrupted by notches or passes1 some of which are wide4 ,near its eastern end occurs the striking gap known as the ,lower narrows 7,plate ,,iv7 through which the ,baraboo river escapes to the northward1 flowing thence to the ,wisconsin4 ,at this narrows the quartzite bluffs rise abruptly #ejj feet above the river4 ,at a and b1 ,plate ,,ii1 there are similar though smaller breaks in the range1 also occupied by streams4 ,the connection between the passes and streams is therefore close4 ,there are many small valleys in the sides of the quartzite ranges 7especially the ,south range7 which do not extend back to their crests1 and therefore do not occasion passes across them4 ,the narrow valleys at a and b in ,plate ,,xxxvii1 known as ,parfrey's and ,dorward's glens1 respectively1 are singularly beautiful gorges1 and merit mention as well from the scenic as from the geologic point of view4 ,wider valleys1 the heads of which do not reach the crest1 occur on the flanks of the main range 7as at d and e1 ,plate ,,ii7 at many points4 ,one such valley occurs east of the north end of the lake 7x1 ,plate ,,xxxvii71 another west of the south end 7y1 ,plate ,,xxxvii71 another on the north face of the west bluff west of the north end of the lake and between the ,east and ,west ,sauk roads1 and still others at greater distances from the lake in both directions4 ,it is manifest that if the valleys were extended headward in the direction of their axes1 they would interrupt the even crest4 ,many of these valleys1 unlike the glens mentioned above1 are very wide in proportion to their length4 ,in some of these capacious valleys there are beds of ,potsdam sandstone1 showing that the valleys existed before the sand of the sandstone was deposited4 ,the structure and constitution of the ridges4--,the quartzite of the ridges is nothing more nor less than altered sandstone4 ,its origin dates from that part of geological time known to geologists as the ,upper ,huronian period4 ,the popular local belief that the quartzite is of igneous origin is without the slightest warrant4 ,it appears to have had its basis in the notion that ,devil's lake occupies an extinct volcanic crater4 ,were this the fact1 igneous rock should be found about it4 ,quartzite is sandstone in which the intergranular spaces have been filled with silica 7quartz7 brought in and deposited by percolating water subsequent to the accumulation of the sand4 ,the conversion of sandstone into quartzite is but a continuation of the process which converts sand into sandstone4 ,the ,potsdam or any other sandstone formation might be converted into quartzite by the same process1 and it would then be a metamorphic rock4 ,like the sandstone1 the quartzite is in layers4 ,this is perhaps nowhere so distinctly shown on a large scale as in the bluffs at ,devil's lake1 and at the east end of the ,devil's nose4 ,on the ,east bluff of the lake1 the stratification is most distinctly seen from the middle of the lake1 from which point the photograph reproduced in ,plate ,,vi was taken4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,v4 ,the ,notch in the ,south quartzite range1 at ,devil's ,lake4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,vi4 ,the east bluff of ,devil's lake1 showing the dip of quartzite 7to the left71 and talus above and below the level where the beds are shown4 ,unlike the sandstone and limestone1 the beds of quartzite are not horizontal4 ,the departure from horizontality1 technically known as the dip1 varies from point to point 7,fig4 #d74 ,in the ,east bluff of the lake as shown in ,plate ,,vi1 the dip is about #ad deg4 to the north4 ,at the ,upper and ,lower narrows of the ,baraboo 7b and c1 ,plate ,,ii7 the beds are essentially vertical1 that is1 they have a dip of about #ij deg44 ,between these extremes1 many intermediate angles have been noted4 ,plate ,,vii represents a view near ,ablemans1 in the ,upper narrows1 where the nearly vertical beds of quartzite are well exposed4 ,the position of the beds in the quartzite is not always easy of recognition4 ,the difficulty is occasioned by the presence of numerous cleavage planes developed in the rock after its conversion into quartzite4 ,some of these secondary cleavage planes are so regular and so nearly parallel to one another as to be easily confused with the bedding planes4 ,this is especially liable to make determinations of the dip difficult1 since the true bedding was often obscured when the cleavage was developed4 ,in spite of the difficulties1 the original stratification can usually be determined where there are good exposures of the rock4 ,at some points the surfaces of the layers carry ripple marks1 and where they are present1 they serve as a ready means of identifying the bedding planes1 even though the strata are now on edge4 ,layers of small pebbles are sometimes found4 ,they were horizontal when the sands of the quartzite were accumulating1 and where they are found they are sufficient to indicate the original position of the beds4 ,aside from the position of the beds1 there is abundant evidence of dynamic action#b in the quartzite4 ,along the railway at ,devil's lake1 half a mile south of the ,cliff ,house1 thin zones of schistose rock may be seen parallel to the bedding planes4 ,these zones of schistose rock a few inches in thickness were developed from the quartzite by the slipping of the rock on either side4 ,this slipping presumably occurred during the adjustment of the heavy beds of quartzite to their new positions1 at the time of tilting and folding1 for no thick series of rock can be folded without more or less slipping of the layers on one another4 ,the slipping 7adjustment7 takes place along the weaker zones4 ,such zones of movement are sometimes known as shear zones1 for the rock on the one side has been sheared 7slipped7 over that on the other4 #b ,irving3 ,the ,baraboo ,quartzite ,ranges4 ,vol4 ,,ii1 ,geology of ,wisconsin1 pp4 #ejd-eai4 ,van ,hise3 ,some ,dynamic ,phenomena ,shown by the ,baraboo ,quartzite ,ranges of ,central ,wisconsin4 ,jour4 of ,geol41 ,vol4 ,i1 pp4 #cdg-cee4 ,illustration3 ,fig4 #d4--;,diagram made by plotting the different dips now at hand along a section from ,a to ,b1 ,plate ,,ii1 and connecting them so as to show the structure indicated by the known data4 ,the full lines1 oblique or vertical1 represent the beds of quartzite4 ,the continuous line above them represents the present surface of the quartzite1 while the dotted lines suggest the continuation of the beds which completed the great folds of which the present exposures appear to be remnants4 ,illustration3 ,fig4 #e4--;,a diagrammatic section showing the relation of the sandstone to the quartzite4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,vii4 ,the ,east ,bluff at the ,upper ,narrows of the ,baraboo near ,ablemans1 showing the vertical position of the beds of quartzite4 ,in the lower right-hand corner1 above the bridge1 appears some breccia4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,viii4 ,vertical shear zone in face of east bluff at ,devil's lake4 ,near the shear zones parallel to the bedding planes1 there is one distinct vertical shear zone 7,plate ,,viii7 three to four feet in width4 ,it is exposed to a height of fully twenty-five feet4 ,along this zone the quartzite has been broken into angular fragments1 and at places the crushing of the fragments has produced a friction clay4 ,slipping along vertical zones would be no necessary part of folding1 though it might accompany it4 ,on the other hand1 it might have preceded or followed the folding4 ,schistose structure probably does not always denote shearing1 at least not the shearing which results from folding4 ,extreme pressure is likely to develop schistosity in rock1 the cleavage planes being at right angles to the direction of pressure4 ,it is not always possible to say how far the schistosity of rock at any given point is the result of shear1 and how far the result of pressure without shear4 ,schistose structure which does not appear to have resulted from shear1 at least not from the shear involved in folding1 is well seen in the isolated quartzite mound about four miles southwest of ,baraboo on the ,west ,sauk road 7f1 ,plate ,,ii74 ,these quartzite schists are to be looked on as metamorphosed quartzite1 just as quartzite is metamorphosed sandstone4 ,at the ,upper narrows of the ,baraboo also 7b1 ,plate ,,ii71 evidence of dynamic action is patent4 ,movement along bedding planes with attendant development of quartz schist has occurred here as at the lake 7,plate ,,ix74 ,besides the schistose belts1 a wide zone of quartzite exposed in the bluffs at this locality has been crushed into angular fragments1 and afterwards re-cemented by white quartz deposited from solution by percolating waters 7,plate ,x74 ,this quartzite is said to be brecciated4 ,within this zone there are spots where the fragments of quartzite are so well rounded as to simulate water-worn pebbles4 ,their forms appear to be the result of the wear of the fragments on one another during the movements which followed the crushing4 ,conglomerate originating in this way is friction conglomerate or ,reibungsbreccia4 ,the crushing of the rock in this zone probably took place while the beds were being folded2 but the brecciated quartzite formed by the re-cementation of the fragments has itself been fractured and broken in such a manner as to show that the formation has suffered at least one dynamic movement since the development of the breccia4 ,that these movements were separated by a considerable interval of time is shown by the fact that the re-cementation of the fragmental products of the first movement preceded the second4 ,what has been said expresses the belief of geologists as to the origin of quartzite and quartz schists2 but because of popular misconception on the point it may here be added that neither the changing of the sandstone into quartzite1 nor the subsequent transformation of the quartzite to schist1 was due primarily to heat4 ,heat was doubtless generated in the mechanical action involved in these changes1 but it was subordinate in importance1 as it was secondary in origin4 ,igneous rock is associated with the quartzite at a few points4 ,at g and h1 ,plate ,,ii there are considerable masses of porphyry1 sustaining such relations to the quartzite as to indicate that they were intruded into the sedimentary beds after the deposition of the latter4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,ix4 ,a mass of quartzite in situ1 in the road through the ,upper ,narrows near ,ableman's4 ,the bedding1 which is nearly vertical1 is indicated by the shading1 while the secondary cleavage approaches horizontality4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,x4 ,brecciated quartzite near ,ablemans in the ,upper ,narrows4 ,the darker parts are quartzite1 the lighter parts the cementing quartz4 ,,iii4 ,,relations ,,of ,,the ,,sandstone ,,of ,,the ,,plain ,,to ,,the ,,quartzite ,,of ,,the ,,ridges4 ,the horizontal beds of ,potsdam sandstone may be traced up to the bases of the quartzite ranges1 where they may frequently be seen to abut against the tilted beds of quartzite4 ,not only this1 but isolated patches of sandstone lie on the truncated edges of the dipping beds of quartzite well up on the slopes1 and even on the crest of the ridge itself4 ,in the former position they may be seen on the ,east bluff at ,devil's lake1 where horizontal beds of conglomerate and sandstone rest on the layers of quartzite which dip #ad deg4 to the north4 ,the stratigraphic relations of the two formations are shown in ,fig4 #e which represents a diagrammatic section from ,a to ,b1 ,plate ,,ii4 ,plate ,,xi is reproduced from a photograph taken in the ,upper narrows of the ,baraboo near ,ablemans1 and shows the relations as they appear in the field4 ,the quartzite layers are here on edge1 and on them rest the horizontal beds of sandstone and conglomerate4 ,similar stratigraphic relations are shown at many other places4 ,this is the relationship of unconformity4 ,such an unconformity as that between the sandstone and the quartzite of this region shows the following sequence of events3 7#a7 the quartzite beds were folded and lifted above the sea in which the sand composing them was originally deposited2 7#b7 a long period of erosion followed1 during which the crests of the folds were worn off2 7#c7 the land then sank1 allowing the sea to again advance over the region2 7#d7 while the sea was here1 sand and gravel derived from the adjacent lands which remained unsubmerged1 were deposited on its bottom4 ,these sands became the ,potsdam sandstone4 ,this sequence of events means that between the deposition of the quartzite and the sandstone1 the older formation was disturbed and eroded4 ,either of these events would have produced an unconformity2 the two make it more pronounced4 ,that the disturbance of the older formation took place before the later sandstone was deposited is evident from the fact that the latter formation was not involved in the movements which disturbed the former4 ,although the sandstone appears in patches on the quartzite ranges1 it is primarily the formation of the surrounding plains1 occupying the broad valley between the ranges1 and the territory surrounding them4 ,the quartzite1 on the other hand1 is the formation of the ridges1 though it outcrops at a few points in the plain4 7,compare ,plates ,,ii and ,,xxxvii47 ,the striking topographic contrasts between the plains and the ridges is thus seen to be closely related to the rock formations involved4 ,it is the hard and resistant quartzite which forms the ridges1 and the less resistant sandstone which forms the lowlands about them4 ,that quartzite underlies the sandstone of the plain is indicated by the occasional outcrops of the former rock on the plain1 and from the fact that borings for deep wells have sometimes reached it where it is not exposed4 ,the sandstone of the plain and the quartzite of the ridges are not everywhere exposed4 ,a deep but variable covering of loose material or mantle rock 7drift7 is found throughout the eastern part of the area1 but it does not extend far west of ,baraboo4 ,this mantle rock is so thick and so irregularly disposed that it has given origin to small hills and ridges4 ,these elevations are superimposed on the erosion topography of the underlying rock1 showing that the drift came into the region after the sandstone1 limestone1 and quartzite had their present relations1 and essentially their present topography4 ,further consideration will be given to the drift in a later part of this report4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,xi4 ,the northeast wall of the ,upper ,narrows1 north of ,ableman's1 showing the horizontal ,potsdam sandstone and conglomerate lying unconformably on the quartzite1 the beds of which are vertical4 ,,part ,,ii4 ,,history ,,of ,,the ,,topography4 ,,chapter ,,ii4 ,,outline ,,of ,,the ,,history ,,of ,,the ,,rock ,,formations ,,which ,,show ,,themselves ,,at ,,the ,,surface4 ,i4 ,,the ,,pre-,,cambrian ,,history ,,of ,,the ,,quartzite4 ,from loose sand to quartzite4--,to understand the geography of a region it is necessary to understand the nature of the materials1 the sculpture of which has made the geography4 ,it has already been indicated that the ,huronian quartzite of which the most prominent elevations of this region are composed1 was once loose sand4 ,even at the risk of repetition1 the steps in its history are here recounted4 ,the source of the sand was probably the still older rocks of the land in the northern part of ,wisconsin4 ,brought down to the sea by rivers1 or washed from the shores of the land by waves1 the sand was deposited in horizontal or nearly horizontal beds at the bottom of the shallow water which then covered central and southern ,wisconsin4 ,later1 perhaps while it was still beneath the sea1 the sand was converted into sandstone1 the change being effected partly by compression which made the mass of sand more compact1 but chiefly by the cementation of its constituent grains into a coherent mass4 ,the water contained in the sand while consolidation was in progress1 held in solution some slight amount of silica1 the same material of which the grains of sand themselves are composed4 ,little by little this silica in solution was deposited on the surfaces of the sand grains1 enlarging them1 and at the same time binding them together4 ,thus the sand became sandstone4 ,continued deposition of silica between and around the grains finally filled the interstitial spaces1 and when this process was completed1 the sandstone had been converted into quartzite4 ,while quartzite is a metamorphic sandstone1 it is not to be understood that sandstone cannot be metamorphosed in other ways4 ,uplift and deformation4 ,dynamic metamorphism4--,after the deposition of the sands which later became the quartzite1 the beds were uplifted and deformed1 as their present positions and relations show4 ,it is not possible to say how far the process of transformation of sand into quartzite was carried while the formation was still beneath the shallow sea in which it was deposited4 ,the sand may have been changed to sandstone1 and the sandstone to quartzite1 before the sea bottom was converted into land1 while on the other hand1 the formation may have been in any stage of change from sand to quartzite1 when that event occurred4 ,if the process of change was then incomplete1 it may have been continued after the sea retired1 by the percolating waters derived from the rainfall of the region4 ,either when first converted into land1 or at some later time1 the beds of rock were folded1 and suffered such other changes as attend profound dynamic movements4 ,the conversion of the sandstone into quartzite probably preceded the deformation1 since many phenomena indicate that the rock was quartzite and not sandstone when the folding took place4 ,for example1 the crushing of the quartzite 7now re-cemented into brecciated quartzite7 at ,ablemans probably dates from the orogenic movements which folded the quartzite1 and the fractured bits of rock often have corners and edges so sharp as to show that the rock was thoroughly quartzitic when the crushing took place4 ,the uplift and deformation of the beds was probably accomplished slowly1 but the vertical and highly tilted strata show that the changes were profound 7see ,fig4 #d74 ,the dynamic metamorphism which accompanied this profound deformation has already been referred to4 ,the folding of the beds involved the slipping of some on others1 and this resulted in the development of quartz schist along the lines of severest movement4 ,changes effected in the texture and structure of the rock under such conditions constitute dynamic metamorphism4 ,in general1 the metamorphic changes effected by dynamic action are much more profound than those brought about in other ways1 and most rocks which have been profoundly metamorphosed1 were changed in this way4 ,dynamic action generates heat1 but contrary to the popular notion1 the heat involved in profound metamorphism is usually secondary1 and the dynamic action fundamental4 ,at the same time that quartz schist was locally developed from the quartzite1 crushing probably occurred in other places4 ,this is demorphism1 rather than metamorphism4 ,erosion of the quartzite4--,when the ,huronian beds were raised to the estate of land1 the processes of erosion immediately began to work on them4 ,the heat and the cold1 the plants and the animals1 the winds1 and especially the rain and the water which came from the melting of the snow1 produced their appropriate effects4 ,under the influence of these agencies the surface of the rock was loosened by weathering1 valleys were cut in it by running water1 and wear and degradation went on at all points4 ,the antagonistic processes of uplift and degradation went on for unnumbered centuries1 long enough for even the slow processes involved to effect stupendous results4 ,degradation was continuous after the region became land1 though uplift may not have been4 ,on the whole1 elevation exceeded degradation1 for some parts of the quartzite finally came to stand high above the level of the sea1--the level to which all degradation tends4 ,fig4 #d conveys some notion of the amount of rock which was removed from the quartzite folds about ,baraboo during this long period of erosion4 ,the south range would seem to represent the stub of one side of a great anticlinal fold1 a large part of which 7represented by the dotted lines7 was carried away1 while the north range may be the core of another fold1 now exposed by erosion4 ,some idea of the geography of the quartzite at the close of this period of erosion may be gained by imagining the work of later times undone4 ,the younger beds covering the quartzite of the plains have a thickness varying from zero to several hundred feet1 and effectually mask the irregularities of the surface of the subjacent quartzite4 ,could they be removed1 the topography of the quartzite would be disclosed1 and found to have much greater relief than the present surface2 that is1 the vertical distance between the crest of the quartzite ridge1 and the surface of the quartzite under the surrounding lowlands1 would be greater than that between the same crest and the surface of the sandstone4 ,but even this does not give the full measure of the relief of the quartzite at the close of the long period of erosion which followed its uplift1 for allowance must be made for the amount of erosion which the crests of the quartzite ranges have suffered since that time4 ,the present surface therefore does not give an adequate conception of the irregularity of the surface at the close of the period of erosion which followed the uplift and deformation of the quartzite4 ,so high were the crests of the quartzite ranges above their surroundings at that time1 that they may well be thought of as mountainous4 ,from this point of view1 the quartzite ranges of today are the partially buried mountains of the pre-,potsdam land of south central ,wisconsin4 ,when the extreme hardness of the quartzite is remembered and also the extent of the erosion which affected it 7,fig4 #d7 before the next succeeding formation was deposited1 it is safe to conclude that the period of erosion was very long4 ,thickness of the quartzite4--,the thickness of the quartzite is not known1 even approximately4 ,the great thickness in the south range suggested by the diagram 7,fig4 #d7 may perhaps be an exaggeration4 ,faulting which has not been discovered may have occurred1 causing repetition of beds at the surface 7,fig4 #f71 and so an exaggerated appearance of thickness4 ,after all allowances have been made1 it is still evident that the thickness of the quartzite is very great4 ,,ii4 ,,the ,,history ,,of ,,the ,,paleozoic ,,strata4 ,the subsidence4--,following the long period of erosion1 the irregular and almost mountainous area of central ,wisconsin was depressed sufficiently to submerge large areas which had been land4 ,the subsidence was probably slow1 and as the sea advanced from the south1 it covered first the valleys and lowlands1 and later the lower hills and ridges1 while the higher hills and ridges of the quartzite stood as islands in the rising sea4 ,still later1 the highest ridges of the region were themselves probably submerged4 ,illustration3 ,fig4 #f4--;,a diagrammatic cross-section1 showing how1 by faulting1 the apparent thickness of the quartzite would be increased4 ,the ,potsdam sandstone 7and conglomerate74--,so soon as the sea began to overspread the region1 its bottom became the site of deposition1 and the deposition continued as long as the submergence lasted4 ,it is to the sediments deposited during the earlier part of this submergence that the name ,potsdam is given4 ,the sources of the sediments are not far to seek4 ,as the former land was depressed beneath the sea1 its surface was doubtless covered with the products of rock decay1 consisting of earths1 sands1 small bits and larger masses of quartzite4 ,these materials1 or at least the finer parts1 were handled by the waves of the shallow waters1 for they were at first shallow1 and assorted and re-distributed4 ,thus the residuary products on the submerged surface1 were one source of sediments4 ,from the shores also1 so long as land areas remained1 the waves derived sediments4 ,these were composed in part of the weathered products of the rock1 and in part of the undecomposed rock against which the waves beat1 after the loose materials had been worn away4 ,these sediments derived from the shore were shifted1 and finally mingled with those derived from the submerged surface4 ,so long as any part of the older land remained above the water1 its streams brought sediments to the sea4 ,these also were shifted by the waves and shore currents1 and finally deposited with the others on the eroded surface of the quartzite4 ,thus sediments derived in various ways1 but inherently essentially similar1 entered into the new formation4 ,illustration3 ,fig4 #g4--;,diagram to illustrate the theoretical disposition of sediments about an island4 ,illustration3 ,fig4 #h4--,same as ,fig4 #g1 except that the land has been depressed4 ,the first material to be deposited on the surface of the quartzite as it was submerged1 was the coarsest part of the sediment4 ,of the sediment derived by the waves from the coasts1 and brought down to the sea by rivers1 the coarsest would at each stage be left nearest the shore1 while the finer was carried progressively farther and farther from it4 ,thus at each stage the sand was deposited farther from the shore than the gravel1 and the mud farther than the sand1 where the water was so deep that the bottom was subject to little agitation by waves4 ,the theoretical distribution of sediments about an island as it was depressed1 is illustrated by the following diagrams1 ,figs4 #g and #h4 ,it will be seen that the surface of the quartzite is immediately overlain by conglomerate1 but that the conglomerate near its top is younger than that near its base4 ,in conformity with this natural distribution of sediments1 the basal beds of the ,potsdam formation are often conglomeratic 7,fig4 #i1 ,plate ,,iii1 ,fig4 #b1 and ,plate ,,xxv74 ,this may oftenest be seen near the quartzite ridges1 for here only is the base of the formation commonly exposed4 ,the pebbles and larger masses of the conglomerate are quartzite1 like that of the subjacent beds1 and demonstrate the source of at least some of the material of the younger formation4 ,that the pebbles and bowlders are of quartzite is significant1 for it shows that the older formation had been changed from sandstone to quartzite1 before the deposition of the ,potsdam sediments4 ,the sand associated with the pebbles may well have come from the breaking up of the quartzite1 though some of it may have been washed in from other sources by the waters in which the deposition took place4 ,illustration3 ,fig4 #i4--,sketch showing relation of basal ,potsdam conglomerate and sandstone to the quartzite1 on the ,east bluff at ,devil's lake1 behind the ,cliff house4 ,the basal conglomerate may be seen at many places1 but nowhere about ,devil's lake is it so well exposed as at ,parfrey's glen 7a1 ,plate ,,xxxvii71 where the rounded stones of which it is composed vary from pebbles1 the size of a pea1 to bowlders more than three feet in diameter4 ,other localities where the conglomerates may be seen to advantage are ,dorward's glen 7b1 ,plate ,,xxxvii71 the ,east bluff at ,devil's lake just above the ,cliff house1 and at the ,upper narrows of the ,baraboo1 above ,ablemans4 ,while the base of the ,potsdam is conglomeratic in many places1 the main body of it is so generally sandstone that the formation as a whole is commonly known as the ,potsdam sandstone4 ,the first effect of the sedimentation which followed submergence was to even up the irregular surface of the quartzite1 for the depressions in the surface were the first to be submerged1 and the first to be filled4 ,as the body of sediment thickened1 it buried the lower hills and the lower parts of the higher ones4 ,the extent to which the ,potsdam formation buried the main ridge may never be known4 ,it may have buried it completely1 for as already stated patches of sandstone are found upon the main range4 ,these patches make it clear that some formation younger than the quartzite once covered essentially all of the higher ridge4 ,other evidence to be adduced later1 confirms this conclusion4 ,it has1 however1 not been demonstrated that the high-level patches of sandstone are ,potsdam4 ,there is abundant evidence that the subsidence which let the ,potsdam seas in over the eroded surface of the ,huronian quartzite was gradual4 ,one line of evidence is found in the cross-bedding of the sandstone 7,plate ,,xii7 especially well exhibited in the ,dalles of the ,wisconsin4 ,the beds of sandstone are essentially horizontal1 but within the horizontal beds there are often secondary layers which depart many degrees from horizontality1 the maximum being about #bd deg44 ,plates ,,xxvii and ,,xii give a better idea of the structure here referred to than verbal description can4 ,the explanation of cross-bedding is to be found in the varying conditions under which sand was deposited4 ,cross-bedding denotes shallow water1 where waves and shore currents were effective at the bottom where deposition is in progress4 ,for a time1 beds were deposited off shore at a certain angle1 much as in the building of a delta 7,fig4 #aj74 ,then by subsidence of the bottom1 other layers with like structure were deposited over the first4 ,by this sequence of events1 the dip of the secondary layers should be toward the open water1 and in this region their dip is generally to the south4 ,at any stage of deposition the waves engendered by storms were liable to erode the surface of the deposits already made1 and new layers1 discordant with those below1 were likely to be laid down upon them4 ,the subordinate layers of each deposit might dip in any direction4 ,if this process were repeated many times during the submergence1 the existing complexity would be explained4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,xii4 ,steamboat rock1--an island in the ,dalles of the ,wisconsin4 ,illustration3 ,fig4 #aj4--;,a diagrammatic cross-section of a delta4 ,the maximum known thickness of the ,potsdam sandstone in ,wisconsin is about #a1jjj feet1 but its thickness in this region is much less4 ,where not capped by some younger formation1 its upper surface has suffered extensive erosion1 and the present thickness therefore falls short of the original4 ,the figures given above may not be too great for the latter4 ,the ,lower ,magnesian limestone4--,the conditions of sedimentation finally changed in the area under consideration4 ,when the sand of the sandstone was being deposited1 adjacent lands were the source whence the sediments were chiefly derived4 ,the evidence that the region was sinking while the sand was being deposited shows that the land masses which were supplying the sand1 were becoming progressively smaller4 ,ultimately the sand ceased to be washed out to the region here described1 either because the water became too deep#c or because the source of supply was too distant4 ,when these relations were brought about1 the conditions were favorable for the deposition of sediments which were to become limestone4 ,these sediments consisted chiefly of the shells of marine life1 together with an unknown amount of lime carbonate precipitated from the waters of the sea4 ,the limestone contains no coarse1 and but little fine material derived from the land1 and the surfaces of its layers are rarely if ever ripple-marked4 ,the materials of which it is made must therefore have been laid down in quiet waters which were essentially free from land-derived sediments4 ,the depth of the water in which it was deposited was not1 however1 great1 for the fossils are not the remains of animals which lived in abysmal depths4 #c ,a few hundred feet would suffice4 ,the deposition of limestone sediments following the deposition of the ,potsdam sands1 does not necessarily mean that there was more or different marine life while the younger formation was making1 but only that the shells1 etc41 which before had been mingled with the sand1 making fossiliferous sandstone1 were now accumulated essentially free from land-derived sediment1 and therefore made limestone4 ,like the sandstone beneath1 the limestone formation has a wide distribution outside the area here under discussion1 showing that conditions similar to those of central ,wisconsin were widely distributed at this time4 ,the beds of limestone are conformable on those of the sandstone1 and the conformable relations of the two formations indicate that the deposition of the upper followed that of the lower1 without interruption4 ,the thickness of the ,lower ,magnesian limestone varies from less than #ajj to more than #bjj feet1 but in this region its thickness is nearer the lesser figure than the larger4 ,the limestone is now present only in the eastern and southern parts of the area1 though it originally covered the whole area4 ,the ,st4 ,peters sandstone4--,overlying the ,lower ,magnesian limestone at a few points1 are seen remnants of ,st4 ,peters sandstone4 ,the constitution of this formation shows that conditions of sedimentation had again changed1 so that sand was again deposited where the conditions had been favorable to the deposition of limestone but a short time before4 ,this formation has been recognized at but two places 7d and e7 within the area shown on ,plate ,,xxxvii1 but the relations at these two points are such as to lead to the conclusion that the formation may once have covered the entire region4 ,this sandstone formation is very like the sandstone below4 ,its materials doubtless came from the lands which then existed4 ,the formation is relatively thin1 ranging from somewhat below to somewhat above #ajj feet4 ,the change from the deposition of limestone sediments to sand may well have resulted from the shoaling of the waters1 which allowed the sand to be carried farther from shore4 ,rise of the land may have accompanied the shoaling of the waters1 and the higher lands would have furnished more and coarser sediments to the sea4 ,younger beds4--,that formations younger than the ,st4 ,peters sandstone once overlaid this part of ,wisconsin is almost certain1 though no remnants of them now exist4 ,evidence which cannot be here detailed#d indicates that sedimentation about the quartzite ridges went on not only until the irregularities of surface were evened up1 but until even the highest peaks of the quartzite were buried1 and that formations as high in the series as the ,niagara limestone once overlay their crests4 ,before this condition was reached1 the quartzite ridges had of course ceased to be islands1 and at the same time had ceased to be a source of supply of sediments4 ,the aggregate thickness of the ,paleozoic beds in the region1 as first deposited1 was probably not less than #a1ejj feet1 and it may have been much more4 ,this thickness would have buried the crests of the quartzite ridges under several hundred feet of sediment 7see ,fig4 #aa74 #d ,jour4 of ,geol41 ,vol4 ,,iii 7pp4 #fee-fg74 ,illustration3 ,fig4 #aa4--,the geological formations of southern ,wisconsin in the order of their occurrence4 ,not all of these are found about ,devil's lake4 ,it is by no means certain that south central ,wisconsin was continuously submerged while this thick series of beds was being deposited4 ,indeed1 there is good reason to believe that there was at least one period of emergence1 followed1 after a considerable lapse of time1 by re-submergence and renewed deposition1 before the ,paleozoic series of the region was complete4 ,these movements1 however1 had little effect on the geography of the region4 ,finally the long period of submergence1 during which several changes in sedimentation had taken place1 came to an end1 and the area under discussion was again converted into land4 ,time involved4--,though it cannot be reduced to numerical terms1 the time involved in the deposition of these several formations of the ,paleozoic must have been very long4 ,it is probably to be reckoned in millions of years1 rather than in denominations of a lower order4 ,climatic conditions4--,little is known concerning the climate of this long period of sedimentation4 ,theoretical considerations have usually been thought to lead to the conclusion that the climate during this part of the earth's history was uniform1 moist1 and warm2 but the conclusion seems not to be so well founded as to command great confidence4 ,the uplift4--,after sedimentation had proceeded to some such extent as indicated1 the sea again retired from central ,wisconsin4 ,this may have been because the sea bottom of this region rose1 or because the sea bottom in other places was depressed1 thus drawing off the water4 ,the topography of this new land1 like the topography of those portions of the sea bottom which are similarly situated1 must have been for the most part level4 ,low swells and broad undulations may have existed1 but no considerable prominences1 and no sudden change of slope4 ,the surface was probably so flat that it would have been regarded as a level surface had it been seen4 ,the height to which the uplift carried the new land surface at the outset must ever remain a matter of conjecture4 ,some estimate may be made of the amount of uplift which the region has suffered since the beginning of this uplift1 but it is unknown how much took place at this time1 and how much in later periods of geological history4 ,the new land surface at once became the site of new activities4 ,all processes of land erosion at once attacked the new surface1 in the effort to carry its materials back to the sea4 ,the sculpturing of this plain1 which1 with some interruption1 has continued to the present day1 has given the region the chief elements of its present topography4 ,but before considering the special history of erosion in this region1 it may be well to consider briefly the general principles and processes of land degradation4 ,,chapter ,,iii4 ,,general ,,outline ,,of ,,rain ,,and ,,river ,,erosion4 ,elements of erosion4--,the general process of subaerial erosion is divisible into the several sub-processes of weathering1 transportation1 and corrasion4#e #e ,there is an admirable exposition of this subject in ,gilbert's ,henry ,mountains4 ,weathering is the term applied to all those processes which disintegrate and disrupt exposed surfaces of rock4 ,it is accomplished chiefly by solution1 changes in temperature1 the wedge-work of ice and roots1 the borings of animals1 and such chemical changes as surface water and air effect4 ,the products of weathering are transported by the direct action of gravity1 by glaciers1 by winds1 and by running water4 ,of these the last is the most important4 ,corrasion is accomplished chiefly by the mechanical wear of streams1 aided by the hard fragments such as sand1 gravel and bowlders1 which they carry4 ,the solution effected by the waters of a stream may also be regarded as a part of corrasion4 ,under ordinary circumstances solution by streams is relatively unimportant1 but where the rock is relatively soluble1 and where conditions are not favorable for abrasion1 solution may be more important than mechanical wear4 ,so soon as sea bottom is raised to the estate of land1 it is attacked by the several processes of degradation4 ,the processes of weathering at once begin to loosen the material of the surface if it be solid2 winds shift the finer particles about1 and with the first shower transportation by running water begins4 ,weathering prepares the material for transportation and transportation leads to corrasion4 ,since the goal of all material transported by running water is the sea1 subaerial erosion means degradation of the surface4 ,erosion without valleys4--,in the work of degradation the valley becomes the site of greatest activity1 and in the following pages especial attention is given to the development of valleys and to the phases of topography to which their development leads4 ,if a new land surface were to come into existence1 composed of materials which were perfectly homogeneous1 with slopes of absolute uniformity in all directions1 and if the rain1 the winds and all other surface agencies acted uniformly over the entire area1 valleys would not be developed4 ,that portion of the rainfall which was not evaporated and did not sink beneath the surface1 would flow off the land in a sheet4 ,the wear which it would effect would be equal in all directions from the center4 ,if the angle of the slope were constant from center to shore1 or if it increased shoreward1 the wear effected by this sheet of water would be greatest at the shore1 because here the sheet of flowing water would be deepest and swiftest1 and therefore most effective in corrasion4 ,the beginning of a valley4--,but land masses as we know them do not have equal and uniform slopes to the sea in all directions1 nor is the material over any considerable area perfectly homogeneous4 ,departure from these conditions1 even in the smallest degree1 would lead to very different results4 ,that the surface of newly emerged land masses would1 as a rule1 not be rough1 is evident from the fact that the bottom of the sea is usually rather smooth4 ,much of it indeed is so nearly plane that if the water were withdrawn1 the eye would scarcely detect any departure from planeness4 ,the topography of a land mass newly exposed either by its own elevation or by the withdrawal of the sea1 would ordinarily be similar to that which would exist in the vicinity of ,necedah and east of ,camp ,douglas1 if the few lone hills were removed1 and the very shallow valleys filled4 ,though such a surface would seem to be moderately uniform as to its slopes1 and homogeneous as to its material1 neither the uniformity nor the homogeneity are perfect1 and the rain water would not run off in sheets1 and the wear would not be equal at all points4 ,let it be supposed that an area of shallow sea bottom is raised above the sea1 and that the elevation proceeds until the land has an altitude of several hundred feet4 ,so soon as it appears above the sea1 the rain falling upon it begins to modify its surface4 ,some of the water evaporates at once1 and has little effect on the surface2 some of it sinks beneath the surface and finds its way underground to the sea2 and some of it runs off over the surface and performs the work characteristic of streams4 ,so far as concerns modifications of the surface1 the run-off is the most important part4 ,the run-off of the surface would tend to gather in the depressions of the surface1 however slight they may be4 ,this tendency is shown on almost every hillside during and after a considerable shower4 ,the water concentrated in the depressions is in excess of that flowing over other parts of the surface1 and therefore flows faster4 ,flowing faster1 it erodes the surface over which it flows more rapidly1 and as a result the initial depressions are deepened1 and washes or gullies are started4 ,should the run-off not find irregularities of slope1 it would1 at the outset1 fail of concentration2 but should it find the material more easily eroded along certain lines than along others1 the lines of easier wear would become the sites of greater erosion4 ,this would lead to the development of gullies1 that is1 to irregularities of slope4 ,either inequality of slope or material may therefore determine the location of a gully1 and one of these conditions is indispensable4 ,once started1 each wash or gully becomes the cause of its own growth1 for the gully developed by the water of one shower1 determines greater concentration of water during the next4 ,greater concentration means faster flow1 faster flow means more rapid wear1 and this means corresponding enlargement of the depression through which the flow takes place4 ,the enlargement effected by successive showers affects a gully in all dimensions4 ,the water coming in at its head carries the head back into the land 7head erosion71 thus lengthening the gully2 the water coming in at its sides wears back the lateral slopes1 thus widening it2 and the water flowing along its bottom deepens it4 ,thus gullies grow to be ravines1 and farther enlargement by the same processes converts ravines into valleys4 ,a river valley therefore is often but a gully grown big4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,xiii4 ,,fig4 #a4 ,a very young valley4 ,illustration3 ,,fig4 #b4 ,a valley in a later stage of development4 ,illustration3 ,,fig4 #c4 ,young valleys4 ,the course of a valley4--,in the lengthening of a gully or valley headward1 the growth will be in the direction of greatest wear4 ,thus in ,plate ,,xiii1 ,fig4 #a1 if the water coming in at the head of the gully effects most wear in the direction a1 the head of the gully will advance in that direction2 if there be most wear in the direction b or c1 the head will advance toward one of these points4 ,the direction of greatest wear will be determined either by the slope of the surface1 or by the nature of the surface material4 ,the slope may lead to the concentration of the entering waters along one line1 and the surface material may be less resistant in one direction than in another4 ,if these factors favor the same direction of head-growth1 the lengthening will be more rapid than if but one is favorable4 ,if there be more rapid growth along two lines1 as b and c1 ,plate ,,xiii1 ,fig4 #a1 than between them1 two gullies may develop 7,plate ,,xiii1 ,fig4 #b74 ,the frequent and tortuous windings common to ravines and valleys are therefore to be explained by the inequalities of slope or material which affected the surface while the valley was developing4 ,tributary valleys4--,following out this simple conception of valley growth1 we have to inquire how a valley system 7a main valley and its tributaries7 is developed4 ,the conditions which determine the location and development of gullies in a new land surface1 determine the location and development of tributary gullies4 ,in flowing over the lateral slopes of a gully or ravine1 the water finds either slope or surface material failing of uniformity4 ,both conditions lead to the concentration of the water along certain lines1 and concentration of flow on the slope of an erosion depression1 be it valley or gully1 leads to the development of a tributary depression4 ,in its growth1 the tributary repeats1 in all essential respects1 the history of its main4 ,it is lengthened headward by water coming in at its upper end1 is widened by side wash1 and deepened by the downward cutting of the water which flows along its axis4 ,the factors controlling its development are the same as those which controlled the valley to which it is tributary4 ,there is one peculiarity of the courses of tributaries which deserves mention4 ,tributaries1 as a rule1 join their mains with an acute angle up stream4 ,in general1 new land surfaces1 such as are now under consideration1 slope toward the sea4 ,if a tributary gully were to start back from its main at right angles1 more water would come in on the side away from the shore1 on account of the seaward slope of the land4 ,this would be true of the head of the gully as well as of other portions1 and the effect would be to turn the head more and more toward parallelism with the main valley4 ,local irregularities of surface may1 and frequently do1 interfere with these normal relations1 so that the general course of a tributary is occasionally at right angles to its main4 ,still more rarely does the general course of a tributary make an acute angle with its main on the down stream side4 ,local irregularities of surface determine the windings of a tributary1 so that their courses for longer or shorter distances may be in violation of the general rule 7c1 ,fig4 #dc72 but on the whole1 the valleys of a system whose history has not been interrupted in a region where the surface material is not notably heterogeneous1 follow the course indicated above4 ,this is shown by nearly every drainage system on the ,atlantic ,coastal plain which represents more nearly than any other portion of our continent1 the conditions here under consideration4 ,fig4 #ab represents the drainage system of the ,mullica river in southern ,new ,jersey and is a type of the ,coastal plain river system4 ,how a valley gets a stream4--,valleys may become somewhat deep and long and wide without possessing permanent streams1 though from their inception they have temporary streams1 the water for which is furnished by showers or melting snow4 ,yet sooner or later1 valleys come to have permanent streams4 ,how are they acquired8 ,does the valley find the stream or the stream the valley8 ,for the answer to these questions1 a brief digression will be helpful4 ,illustration3 ,fig4 #ab4--;,a typical river system of the ,coastal plain type4 ,in cultivated regions1 wells are of frequent occurrence4 ,in a flat region of uniform structure1 the depth at which well water may be obtained is essentially constant at all points4 ,if holes 7wells #a and #b1 ,fig4 #ac7 be excavated below this level1 water seeps into them1 and in a series of wells the water stands at a nearly common level4 ,this means that the sub-structure is full of water up to that level4 ,these relations are illustrated by ,fig4 #ac4 ,the diagram represents a vertical section through a flat region from the surface 7s s7 down below the bottom of wells4 ,the water stands at the same level in the two cells 7#a and #b71 and the plane through them1 at the surface of the water1 is the ground water level4 ,if in such a surface a valley were to be cut until its bottom was below the ground water level1 the water would seep into it1 as it does into the wells2 and if the amount were sufficient1 a permanent stream would be established4 ,this is illustrated in ,fig4 #ac4 ,the line ,a ,a represents the ground water level1 and the level at which the water stands in the wells1 under ordinary circumstances4 ,the bottom of the valley is below the level of the ground water1 and the water seeps into it from either side4 ,its tendency is to fill the valley to the level ,a ,a4 ,but instead of accumulating in the open valley as it does in the enclosed wells1 it flows away1 and the ground water level on either hand is drawn down4 ,illustration3 ,fig4 #ac4--;,diagram illustrating the relations of ground water to streams4 ,the level of the ground water fluctuates4 ,it is depressed when the season is dry 7,a' ,a'71 and raised when precipitation is abundant 7,a'' ,a''74 ,when it is raised1 the water in the wells rises1 and the stream in the valley is swollen4 ,when it falls1 the ground water surface is depressed1 and the water in the wells becomes lower4 ,if the water surface sinks below the bottom of the wells1 the wells go dry2 if below the bottom of the valley1 the valley becomes for the time being1 a dry run4 ,when a well is below the lowest ground-water level its supply of water never fails1 and when the valley is sufficiently below the same level1 its stream does not cease to flow1 even in periods of drought4 ,on account of the free evaporation in the open valley1 the valley depression must be somewhat below the level necessary for a well1 in order that the flow may be constant4 ,it will be seen that intermittent streams1 that is1 streams which flow in wet seasons and fail in dry1 are intermediate between streams which flow after showers only1 and those which flow without interruption4 ,in the figure the stream would become dry if the ground water level sank to ,a' ,a'4 ,it is to be noted that a permanent stream does not normally precede its valley1 but that the valley1 developed through gully-hood and ravine-hood to valley-hood by means of the temporary streams supplied by the run-off of occasional showers1 finds a stream1 just as diggers of wells find water4 ,the case is not altered if the stream be fed by springs1 for the valley finds the spring1 as truly as the well-digger finds a vein of water4 ,limits of a valley4--,so soon as a valley acquires a permanent stream1 its development goes on without the interruption to which it was subject while the stream was intermittent4 ,the permanent stream1 like the temporary one which preceded it1 tends to deepen and widen its valley1 and1 under certain conditions1 to lengthen it as well4 ,the means by which these enlargements are affected are the same as before4 ,there are limits1 however1 in length1 depth1 and width1 beyond which a valley may not go4 ,no stream can cut below the level of the water into which it flows1 and it can cut to that level only at its outlet4 ,up stream from that point1 a gentle gradient will be established over which the water will flow without cutting4 ,in this condition the stream is at grade4 ,its channel has reached baselevel1 that is1 the level to which the stream can wear its bed4 ,this grade is1 however1 not necessarily permanent1 for what was baselevel for a small stream in an early stage of its development1 is not necessarily baselevel for the larger stream which succeeds it at a later time4 ,weathering1 wash1 and lateral corrasion of the stream continue to widen the valley after it has reached baselevel4 ,the bluffs of valleys are thus forced to recede1 and the valley is widened at the expense of the upland4 ,two valleys widening on opposite sides of a divide1 narrow the divide between them1 and may ultimately wear it out4 ,when this is accomplished1 the two valleys become one4 ,the limit to which a valley may widen on either side is therefore its neighboring valley1 and since1 after two valleys have become one by the elimination of the ridge between them1 there are still valleys on either hand1 the final result of the widening of all valleys must be to reduce all the area which they drain to baselevel4 ,as this process goes forward1 the upper flat into which the valleys were cut is being restricted in area1 while the lower flats developed by the streams in the valley bottoms are being enlarged4 ,thus the lower flats grow at the expense of the higher4 ,there are also limits in length which a valley may not exceed4 ,the head of any valley may recede until some other valley is reached4 ,the recession may not stop even there1 for if1 on opposite sides of a divide1 erosion is unequal1 as between #a;,a and #a;,b1 ,fig4 #ad1 the divide will be moved toward the side of less rapid erosion1 and it will cease to recede only when erosion on the two sides becomes equal 7#d;,a and #d;,b74 ,in homogeneous material this will be when the slopes on the two sides are equal4 ,illustration3 ,fig4 #ad4--;,diagram showing the shifting of a divide4 ,the slopes #a;,a and #a;,b are unequal4 ,the steeper slope is worn more rapidly and the divide is shifted from #a to #d1 where the two slopes become equal and the migration of the divide ceases4 ,it should be noted that the lengthening of a valley headward is not normally the work of the permanent stream1 for the permanent stream begins some distance below the head of the valley4 ,at the head1 therefore1 erosion goes on as at the beginning1 even after a permanent stream is acquired4 ,under certain circumstances1 the valley may be lengthened at its debouchure4 ,if the detritus carried by it is deposited at its mouth1 or if the sea bottom beyond that point rise1 the land may be extended seaward1 and over this extension the stream will find its way4 ,thus at their lower1 as well as at their upper ends1 both the stream and its valley may be lengthened4 ,a cycle of erosion4--,if1 along the borders of a new-born land mass1 a series of valleys were developed1 essentially parallel to one another1 they would constitute depressions separated by elevations1 representing the original surface not yet notably affected by erosion 7see ,plate ,,xiv1 ,fig4 #a74 ,these inter-valley areas might at first be wide or narrow1 but in process of time they would necessarily become narrow1 for1 once1 a valley is started1 all the water which enters it from either side helps to wear back its slopes1 and the wearing back of the slopes means the widening of the valleys on the one hand and the narrowing of the inter-valley ridges on the other4 ,not only would the water running over the slopes of a valley wear back its walls1 but many other processes conspire to the same end4 ,the wetting and drying1 the freezing and the thawing1 the roots of plants and the borings of animals1 all tend to loosen the material on the slopes or walls of the valleys1 and gravity helps the loosened material to descend4 ,once in the valley bottom1 the running water is likely to carry it off1 landing it finally in the sea4 ,thus the growth of the valley is not the result of running water alone1 though this is the most important single factor in the process4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,xiv4 ,,fig4 #a4 ,the same valleys as shown in ,plate ,,xiii1 ,fig4 #c1 in a later stage of development4 ,illustration3 ,,fig4 #b4 ,same valleys as shown in ,fig4 #a1 in a still later stage of development4 ,even if valleys developed no tributaries1 they would1 in the course of time1 widen to such an extent as to nearly obliterate the intervening ridges4 ,the surface1 however1 would not easily be reduced to perfect flatness4 ,for a long time at least there would remain something of slope from the central axis of the former inter-stream ridge1 toward the streams on either hand2 but if the process of erosion went on for a sufficiently long period of time1 the inter-stream ridge would be brought very low1 and the result would be an essentially flat surface between the streams1 much below the level of the old one4 ,the first valleys which started on the land surface 7see ,plate ,,xiii1 ,fig4 #c7 would be almost sure to develop numerous tributaries4 ,into tributary valleys water would flow from their sides and from their heads1 and as a result they would widen and deepen and lengthen just as their mains had done before them4 ,by lengthening headward they would work back from their mains some part1 or even all of the way across the divides separating the main valleys4 ,by this process1 the tributaries cut the divides between the main streams into shorter cross-ridges4 ,with the development of tributary valleys there would be many lines of drainage instead of two1 working at the area between two main streams4 ,the result would be that the surface would be brought low much more rapidly1 for it is clear that many valleys within the area between the main streams1 widening at the same time1 would diminish the aggregate area of the upland much more rapidly than two alone could do4 ,the same thing is made clear in another way4 ,it will be seen 7,plate ,,xiv1 ,figs4 #a and #b7 that the tributaries would presently dissect an area of uniform surface1 tending to cut it into a series of short ridges or hills4 ,in this way the amount of sloping surface is greatly increased1 and as a result1 every shower would have much more effect in washing loose materials down to lower levels1 whence the streams could carry them to the sea4 ,illustration3 ,fig4 #ae4--;,cross-sections showing various stages of erosion in one cycle4 ,the successive stages in the process of lowering a surface are suggested by ,fig4 #ae1 which represents a series of cross-sections of a land mass in process of degradation4 ,the uppermost section represents a level surface crossed by young valleys4 ,the next lower represents the same surface at a later stage1 when the valleys have grown larger1 while the third and succeeding sections represent still later stages in the process of degradation4 ,plate ,,xiii1 ,fig4 #c1 and ,plate ,,xiv1 ,figs4 #a and #b1 represent in another way the successive stages of stream work in the general process of degradation4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,xv4 ,diagram illustrating how a hard inclined layer of rock becomes a ridge in the process of degradation4 ,in this manner a series of rivers1 operating for a sufficiently long period of time1 might reduce even a high land mass to a low level1 scarcely above the sea4 ,the new level would be developed soonest near the sea1 and the areas farthest from it would be the last--other things being equal--to be brought low4 ,the time necessary for the development of such a surface is known as a cycle of erosion1 and the resulting surface is a base-level plain1 that is1 a plain as near sea level as river erosion can bring it4 ,at a stage shortly preceding the base-level stage the surface would be a peneplain4 ,a peneplain1 therefore1 is a surface which has been brought toward1 but not to base-level4 ,land surfaces are often spoken of as young or old in their erosion history according to the stage of advancement which has been made toward base-leveling4 ,thus the ,colorado canyon1 deep and impressive as it is1 is1 in terms of erosion1 a young valley1 for the river has done but a small part of the work which must be done in order to bring its basin to baselevel4 ,effects of unequal hardness4--,the process of erosion thus sketched would ultimately bring the surface of the land down to base-level1 and in case the material of the land were homogeneous1 the last points to be reduced would be those most remote from the axes of the streams doing the work of leveling4 ,but if the material of the land were of unequal hardness1 those parts which were hardest would resist the action of erosion most effectively4 ,the areas of softer rock would be brought low1 and the outcrops of hard rock 7,plate ,,xv7 would constitute ridges during the later stages of an erosion cycle4 ,if there were bodies of hard rock1 such as the ,baraboo quartzite1 surrounded by sandstone1 such as the ,potsdam1 the sandstone on either hand would be worn down much more readily than the quartzite1 and in the course of degradation the latter would come to stand out prominently4 ,the region in the vicinity of ,devil's lake is in that stage of erosion in which the quartzite ridges are conspicuous 7,plate ,,xxxvii74 ,the less resistant sandstone has been removed from about them1 and erosion has not advanced so far since the isolation of the quartzite ridges as to greatly lower their crests4 ,the harder strata are at a level where surface water can still work effectively1 even though slowly1 upon them1 and in spite of their great resistance they will ultimately be brought down to the common level4 ,it will be seen that1 from the point of view of subaerial erosion1 a base-level plain is the only land surface which is in a condition of approximate stability4 ,falls and rapids4--,if in lowering its channel a stream crosses one layer of rock much harder than the next underlying1 the deepening will go on more rapidly on the less resistant bed4 ,where the stream crosses from the harder to the less hard1 the gradient is likely to become steep1 and a rapids is formed4 ,these conditions are suggested in ,fig4 #af which represents the successive profiles 7a b1 a c1 d e1 f e1 g e1 and h e7 of a stream crossing from a harder to a softer formation4 ,below the point a the stream is flowing over rock which is easily eroded1 while above that point its course is over a harder formation4 ,just below a 7profile a b7 the gradient has become so steep that there are rapids4 ,under these conditions1 erosion is rapid just beyond the crossing of the hard layer1 and the gradient becomes higher and higher4 ,when the steep slope of the rapids approaches verticality1 the rapids become a fall 7profile a c74 ,illustration3 ,fig4 #af4--;,diagram to illustrate the development of a rapid and fall4 ,the upper layer is harder than the strata below4 ,the successive profiles of the stream below the hard layer are represented by the lines a b1 a c1 d e1 f e1 g e1 and h e4 ,as the water falls over the precipitous face and strikes upon the softer rock below1 part of it rebounds against the base of the vertical face 7,fig4 #af74 ,the result of wear at this point is the undermining of the hard layer above1 and sooner or later1 portions of it will fall4 ,this will occasion the recession of the fall 7profile d e and f e74 ,as the fall recedes1 it grows less and less high4 ,when the recession has reached the point i1 or1 in other words1 when the gradient of the stream below the fall crosses the junction of the beds of unequal hardness1 as it ultimately must1 effective undermining ceases1 and the end of the fall is at hand4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,xvi4 ,skillett ,falls1 in the ,potsdam formation1 three miles southwest of ,baraboo4 ,the several small falls are occasioned by slight inequalities in the hardness of the layers4 ,when the effective undercutting ceases because the softer bed is no longer accessible1 the point of maximum wear is transferred to the top of the hard bed just where the water begins to fall 7g1 ,fig4 #af74 ,the wear here is no greater than before1 though it is greater relatively4 ,the relatively greater wear at this point destroys the verticality of the face1 converting it into a steep slope4 ,when this happens1 the fall is a thing of the past1 and rapids succeed4 ,with continued flow the bed of the rapids becomes less and less steep1 until it is finally reduced to the normal gradient of the stream 7h e71 when the rapids disappear4 ,when thin layers of rock in a stream's course vary in hardness1 softer beds alternating with harder ones1 a series of falls such as shown in ,plate ,,xvi1 may result4 ,as they work up stream1 these falls will be obliterated one by one4 ,thus it is seen that falls and rapids are not permanent features of the landscape4 ,they belong to the younger period of a valley's history1 rather than to the older4 ,they are marks of topographic youth4 ,narrows4--,where a stream crosses a hard layer or ridge of rock lying between softer ones1 the valley will not widen so rapidly in the hard rock as above and below4 ,if the hard beds be vertical1 so that their outcrop is not shifted as the degradation of the surface proceeds1 a notable constriction of the valley results4 ,such a constriction is a narrows4 ,the ,upper and ,lower narrows of the ,baraboo 7,plate ,,iv7 are good examples of the effect of hard rock on the widening of a valley4 ,erosion of folded strata4--,the processes of river erosion would not be essentially different in case the land mass upon which erosion operated were made of tilted and folded strata4 ,the folds would1 at the outset1 determine the position of the drainage lines1 for the main streams would flow in the troughs 7synclines7 between the folds 7anticlines74 ,once developed1 the streams would lower their beds1 widen their valleys1 and lengthen their courses1 and in the long process of time they would bring the area drained nearly to sea-level1 just as in the preceding case4 ,it was under such conditions that the general processes of subaerial erosion operated in south central ,wisconsin1 after the uplift of the quartzite and before the deposition of the ,potsdam sandstone4 ,it was then that the principal features of the topography of the quartzite were developed4 ,in regions of folded strata1 certain beds are likely to be more resistant than others4 ,where harder beds alternate with softer1 the former finally come to stand out as ridges1 while the outcrops of the latter mark the sites of the valleys4 ,such alternations of beds of unequal resistance give rise to various peculiarities of drainage1 particularly in the courses of tributaries4 ,these peculiarities find no illustration in this region and are not here discussed4 ,base-level plains and peneplains4--,it is important to notice that a plane surface 7base-level7 developed by streams could only be developed at elevations but slightly above the sea1 that is1 at levels at which running water ceases to be an effective agent of erosion2 for so long as a stream is actively deepening its valley1 its tendency is to roughen the area which it drains1 not to make it smooth4 ,the ,colorado river1 flowing through high land1 makes a deep gorge4 ,all the streams of the western plateaus have deep valleys1 and the manifest result of their action is to roughen the surface2 but given time enough1 and the streams will have cut their beds to low gradients4 ,then1 though deepening of the valleys will cease1 widening will not1 and inch by inch and shower by shower the elevated lands between the valleys will be reduced in area1 and ultimately the whole will be brought down nearly to the level of the stream beds4 ,this is illustrated by ,fig4 #ae4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,xvii4 ,a group of mounds on the plain southwest from ,camp ,douglas4 ,the base-level surface is well shown1 and above it rise the remnants of the higher plain from which the lower was reduced4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,xviii4 ,castle ,rock near ,camp ,douglas4 ,in this view the relation of the erosion remnant to the extensive base-leveled surface is well shown4 ,it is important to notice further that if the original surface on which erosion began is level1 there is no stage intermediate between the beginning and the end of an erosion cycle1 when the surface is again level1 or nearly so1 though in the stage of a cycle next preceding the last--the peneplain stage 7fourth profile1 ,fig4 #ae7--the surface approaches flatness4 ,it is also important to notice that when streams have cut a land surface down to the level at which they cease to erode1 that surface will still possess some slight slope1 and that to seaward4 ,no definite degree of slope can be fixed upon as marking a base-level4 ,the angle of slope which would practically stop erosion in a region of slight rainfall would be great enough to allow of erosion if the precipitation were greater4 ,all that can be said1 therefore1 is that the angle of slope must be low4 ,the ,mississippi has a fall of less than a foot per mile for some hundreds of miles above the gulf4 ,a small stream in a similar situation would have ceased to lower its channel before so low a gradient was reached4 ,the nearest approach to a base-leveled region within the area here under consideration is in the vicinity of ,camp ,douglas and ,necedah 7see ,plate ,i74 ,this is indeed one of the best examples of a base-leveled plain known4 ,here the broad plain1 extending in some directions as far as the eye can reach1 is as low as it could be reduced by the streams which developed it4 ,the erosion cycle which produced the plain was1 however1 not completed1 for above the plain rise a few conspicuous hills 7,plates ,,xvii and ,,xviii1 and ,fig4 #ag71 and to the west of it lie the highlands marking the level from which the low plain was reduced4 ,where a region has been clearly base-leveled1 isolated masses or ridges of resistant rock may still stand out conspicuously above it4 ,the quartzite hill at ,necedah is an example4 ,such hills are known as monadnocks4 ,this name was taken from ,mount ,monadnock which owes its origin to the removal of the surrounding less resistant beds4 ,the name has now become generic4 ,many of the isolated hills on the peneplain east of ,camp ,douglas are perhaps due to superior resistance1 though the rock of which they are composed belongs to the same formation as that which has been removed4 ,illustration3 ,fig4 #ag4--,sketch1 looking northwest from ,camp ,douglas4 ,,characteristics ,,of ,,valleys ,,at ,,various ,,stages ,,of ,,development4 ,in the early stages of its development a depression made by erosion has steep lateral slopes1 the exact character of which is determined by many considerations4 ,its normal cross-section is usually described as ,v-shaped 7,fig4 #ah74 ,in the early stages of its development1 especially if in unconsolidated material1 the slopes are normally convex inward4 ,if cut in solid rock1 the cross section may be the same1 though many variations are likely to appear1 due especially to the structure of the rock and to inequalities of hardness4 ,if a stream be swift enough to carry off not only all the detritus descending from its slopes1 but to abrade its bed effectively besides1 a steep-sided gorge develops4 ,if it becomes deep1 it is a canyon4 ,for the development of a canyon1 the material of the walls must be such as is capable of standing at a high angle4 ,a canyon always indicates that the down-cutting of a stream keeps well ahead of the widening4 ,illustration3 ,fig4 #ah4--;,diagrammatic cross-section of a young valley4 ,of young valleys in loose material 7drift7 there are many examples in the eastern portion of the area here described4 ,shallow canyons or gorges in rock are also found4 ,the gorge of ,skillett creek at and above the ,pewit's nest about three miles southwest from ,baraboo1 the gorge of ,dell creek two miles south of ,kilbourn ,city1 and the ,dalles of the ,wisconsin at ,kilbourn ,city may serve as illustrations of this type of valley4 ,illustration3 ,fig4 #ai4--;,diagrammatic profile of a young valley4 ,the profile of a valley at the stage of its development corresponding to the above section is represented diagrammatically by the curve ,a ,b in ,fig4 #ai4 ,the sketch 7,pl4 ,,xix1 ,fig4 #a7 represents a bird's-eye view of a valley in the same stage of development4 ,illustration3 ,fig4 #bj4--;,diagrammatic cross-section of a valley at a stage corresponding with that shown in ,plate ,,xix1 ,fig4 #b4 ,at a stage of development later than that represented by the ,v-shaped cross-section1 the corresponding section is ,u-shaped1 as shown in ,fig4 #bj4 ,the same form is sketched in ,plate ,,xix1 ,fig4 #b4 ,this represents a stage of development where detritus descending the slopes is not all carried away by the stream1 and where the valley is being widened faster than it is deepened4 ,its slopes are therefore becoming gentler4 ,the profile of the valley at this stage would be much the same as that in the preceding1 except that the gradient in the lower portion would be lower4 ,still later the cross section of the valley assumes the shape shown in ,fig4 #ba1 and in perspective the form sketched in ,plate ,,xx1 ,fig4 #a4 ,this transformation is effected partly by erosion1 and partly by deposition in the valley4 ,when a stream has cut its valley as low as conditions allow1 it becomes sluggish4 ,a sluggish stream is easily turned from side to side1 and1 directed against its banks1 it may undercut them1 causing them to recede at the point of undercutting4 ,in its meanderings1 it undercuts at various points at various times1 and the aggregate result is the widening of the valley4 ,by this process alone the stream would develop a flat grade4 ,at the same time all the drainage which comes in at the sides tends to carry the walls of the valley farther from its axis4 ,illustration3 ,fig4 #ba4--;,diagrammatic cross-section of a valley at a stage later than that shown in ,fig4 #bj4 ,a sluggish stream is also generally a depositing stream4 ,its deposits tend to aggrade 7build up7 the flat which its meanderings develop4 ,when a valley bottom is built up1 it becomes wider at the same time1 for the valley is1 as a rule1 wider at any given level than at any lower one4 ,thus the ,u-shaped valley is finally converted into a valley with a flat bottom1 the flat being due in large part to erosion1 and in smaller part to deposition4 ,under exceptional circumstances the relative importance of these two factors may be reversed4 ,it will be seen that the cross-section of a valley affords a clue to its age4 ,a valley without a flat is young1 and increasing age is indicated by increasing width4 ,valleys illustrating all stages of development are to be found in the ,devil's lake region4 ,the valley of ,honey creek southwest of ,devil's lake may be taken as an illustration of a valley at an intermediate stage of development1 while examples of old valleys are found in the flat country about ,camp ,douglas and ,necedah4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,xix4 ,,fig4 #a4 ,sketch of a valley at the stage of development corresponding to the cross section shown in ,fig4 #ah4 ,illustration3 ,,fig4 #b4 ,sketch of a valley at the stage of development corresponding to the cross section shown in ,fig4 #bj4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,xx4 ,,fig4 #a4 ,sketch of a part of a valley at the stage of development corresponding to the cross section shown in ,fig #ba4 ,illustration3 ,,fig4 #b4 ,sketch of a section of the ,baraboo valley4 ,transportation and ,deposition4 ,sediment is carried by streams in two ways3 7#a7 by being rolled along the bottom1 and 7#b7 by being held in suspension4 ,dissolved mineral matter 7which is not sediment7 is also carried in the water4 ,by means of that rolled along the bottom and carried in suspension1 especially the former1 the stream as already stated abrades its bed4 ,the transporting power of a stream of given size varies with its velocity4 ,increase in the declivity or the volume of a stream increases its velocity and therefore its transportive power4 ,the transportation effected by a stream is influenced 7#a7 by its transporting power1 and 7#b7 by the size and amount of material available for carriage4 ,fine material is carried with a less expenditure of energy than an equal amount of coarse4 ,with the same expenditure of energy therefore a stream can carry a greater amount of the former than of the latter4 ,since the transportation effected by a stream is dependent on its gradient1 its size1 and the size and amount of material available1 it follows that when these conditions change so as to decrease the carrying power of the river1 deposition will follow1 if the stream was previously fully loaded4 ,in other words1 a stream will deposit when it becomes overloaded4 ,overloading may come about in the following ways3 7#a7 ,by decrease in gradient1 checking velocity and therefore carrying power2 7#b7 by decrease in amount of water1 which may result from evaporation1 absorption1 etc42 7#c7 by change in the shape of the channel1 so that the friction of flow is increased1 and therefore the force available for transportation lessened2 7#d7 by lateral drainage bringing in more sediment than the main stream can carry2 7#e7 by change in the character of the material to which the stream has access2 for if it becomes finer1 the coarse material previously carried will be dropped1 and the fine taken2 and 7#f7 by the checking of velocity when a stream flows into a body of standing water4 ,topographic forms resulting from stream deposition4--,the topographic forms resulting from stream deposition are various4 ,at the bottoms of steep slopes1 temporary streams build alluvial cones or fans4 ,along its flood-plain portion1 a stream deposits more or less sediment on its flats4 ,the part played by deposition in building a river flat has already been alluded to4 ,a depositing stream often wanders about in an apparently aimless way across its flood plain4 ,at the bends in its course1 cutting is often taking place on the outside of a curve while deposition is going on in the inside4 ,the valley of the ,baraboo illustrates this process of cutting and building4 ,fig4 #b1 ,plate ,,xx1 is based upon the features of the valley within the city of ,baraboo4 ,besides depositing on its flood-plain1 a stream often deposits in its channel4 ,any obstruction of a channel which checks the current of a loaded stream occasions deposition4 ,in this way bars are formed4 ,once started1 the bar increases in size1 for it becomes an obstacle to flow1 and so the cause of its own growth4 ,it may be built up nearly to the surface of the stream1 and in low water1 it may become an island by the depression of the surface water4 ,in some parts of its course1 as about ,merrimac1 the ,wisconsin river is marked by such islands at low water1 and by a much larger number of bars4 ,at their debouchures1 streams give up their loads of sediment4 ,under favorable conditions deltas are built1 but delta-building has not entered into the physical history of this region to any notable extent4 ,rejuvenation of ,streams4 ,after the development of a base-level plain1 its surface would suffer little change 7except that effected by underground water7 so long as it maintained its position4 ,but if1 after its development1 a base-level plain were elevated1 the old surface in a new position would be subject to a new series of changes identical in kind with those which had gone before4 ,the elevation would give the established streams greater fall1 and they would reassume the characteristics of youth4 ,the greater fall would accelerate their velocities2 the increased velocities would entail increased erosion2 increased erosion would result in the deepening of the valleys1 and the deepening of the valleys would lead to the roughening of the surface4 ,but in the course of time1 the rejuvenated streams would have cut their valleys as low as the new altitude of the land permitted1 that is1 to a new base-level4 ,the process of deepening would then stop1 and the limit of vertical relief which the streams were capable of developing1 would be attained4 ,but the valleys would not stop widening when they stopped deepening1 and as they widened1 the intervening divides would become narrower1 and ultimately lower4 ,in the course of time they would be destroyed1 giving rise to a new level surface much below the old one1 but developed in the same position which the old one occupied when it originated2 that is1 a position but little above sea level4 ,if at some intermediate stage in the development of a second base-level plain1 say at a time when the streams1 rejuvenated by uplift1 had brought half the elevated surface down to a new base-level1 another uplift were to occur1 the half completed cycle would be brought to an end1 and a new one begun4 ,the streams would again be quickened1 and as a result they would promptly cut new and deeper channels in the bottoms of the great valleys which had already been developed4 ,the topography which would result is suggested by the following diagram 7,fig4 #bb7 which illustrates the cross-section which would be found after the following sequence of events3 7#a7 ,the development of a base-level1 ,a ,a2 7#b7 uplift1 rejuvenation of the streams1 and a new cycle of erosion half completed1 the new base-level being at ,b ,b2 7#c7 a second uplift1 bringing the second 7incomplete7 cycle of erosion to a close1 and by rejuvenating the streams1 inaugurating the third cycle4 ,as represented in the diagram1 the third cycle has not progressed far1 being represented only by the narrow valley ,c4 ,the base-level is now #b-b1 and the valley represented in the diagram has not yet reached it4 ,illustration3 ,fig4 #bb4--;,diagram 7cross-section71 illustrating the topographic effect of rejuvenation by uplift4 ,illustration3 ,fig4 #bc4--,normal profile of a valley bottom in a non-mountainous region4 ,the rejuvenation of a stream shows itself in another way4 ,the normal profile of a valley bottom in a non-mountainous region is a gentle curve1 concave upward with gradient increasing from debouchure to source4 ,such a profile is shown in ,fig4 #bc4 ,fig4 #bd1 on the other hand1 is the profile of a rejuvenated stream4 ,the valley once had a profile similar to that shown in ,fig4 #bc4 ,below ,b its former continuation is marked by the dotted line ,b ,c4 ,since rejuvenation the stream has deepened the lower part of its valley1 and established there a profile in harmony with the new conditions4 ,the upper end of the new curve has not yet reached beyond ,b4 ,illustration3 ,fig4 #bd4--,profile of a stream rejuvenated by uplift4 ,underground ,water4 ,in what has preceded1 reference has been made only to the results accomplished by the water which runs off over the surface4 ,the water which sinks beneath it is1 however1 of no small importance in reducing a land surface4 ,the enormous amount of mineral matter in solution in spring water bears witness to the efficiency of the ground water in dissolving rock1 for since the water did not contain the mineral matter when it entered the soil1 it must have acquired it below the surface4 ,by this means alone1 areas of more soluble rock are lowered below those of less solubility4 ,furthermore1 the water is still active as a solvent agent after a surface has been reduced to so low a gradient that the run-off ceases to erode mechanically4 ,,chapter ,,iv4 ,,erosion ,,and ,,the ,,development ,,of ,,striking ,,scenic ,,features4 ,the uplift following the period of ,paleozoic deposition in south central ,wisconsin1 inaugurated a period of erosion which1 with some interruptions1 has continued to the present day4 ,the processes of weathering began as soon as the surface was exposed to the weather1 and corrasion by running water began with the first shower which fell upon it4 ,the sediment worn from the land was carried back to the sea1 there to be used in the building of still younger formations4 ,the rate of erosion of a land surface depends in large measure upon its height4 ,as a rule1 it is eroded rapidly if high1 and but slowly if low4 ,it is not known whether the lands of central ,wisconsin rose to slight or to great heights at the close of the period of ,paleozoic sedimentation4 ,it is therefore not known whether the erosion was at the outset rapid or slow4 ,if the land of southern ,wisconsin remained low for a time after the uplift which brought the ,paleozoic sedimentation to a close1 weathering would have exceeded transportation and corrasion4 ,a large proportion of the rainfall would have sunk beneath the surface1 and found its way to the sea by subterranean routes4 ,loosening of material by alternate wetting and drying1 expansion and contraction1 freezing and thawing1 and by solution1 might have gone on steadily1 but so long as the land was low1 there would have been little run-off1 and that little would have flowed over a surface of gentle slopes1 and transportation would have been at a minimum4 ,on the whole1 the degradation of the land under these conditions could not have advanced rapidly4 ,if1 on the other hand1 the land was raised promptly to a considerable height1 erosion would have been vigorous at the outset4 ,the surface waters would soon have developed valleys which the streams would have widened1 deepened and lengthened4 ,both transportation and corrasion would have been active1 and whatever material was prepared for transportation by weathering1 and brought into the valleys by side-wash1 would have been hurried on its way to the sea1 and degradation would have proceeded rapidly4 ,establishment of drainage4--,valleys were developed in this new land surface according to the principles already set forth4 ,between the valleys there were divides1 which became higher as the valleys became deeper1 and narrower as the valleys widened4 ,ultimately the ridges were lowered1 and many of them finally eliminated in the manner already outlined4 ,the distance below the original surface and that at which the first series of new flats were developed is conjectural1 but it would have depended on the height of the land4 ,so far as can now be inferred1 the new base-plain toward which the streams cut may have been #djj or #ejj feet below the crests of the quartzite ridges4 ,it was at this level that the oldest base-plain of which this immediate region shows evidence1 was developed4 ,had the quartzite ranges not been completely buried by the ,paleozoic sediments1 they would have appeared as ridges on the new land surface1 and would have had a marked influence on the development of the drainage of the newly emerged surface4 ,but as the ranges were probably completely buried1 the drainage lines were established regardless of the position of the hard1 but buried ridges4 ,when in the process of degradation the quartzite surfaces were reached1 the streams encountered a formation far more resistant than the surrounding sandstone and limestone4 ,as the less resistant strata were worn away1 the old quartzite ridges1 long buried1 again became prominent topographic features4 ,in this condition they were resurrected mountains4 ,if1 when erosion on the uplifted surface of ,paleozoic rocks began1 a valley had been located directly over the buried quartzite ridge1 and along its course1 it would have been deepened normally until its bottom reached the crest of the hard formation4 ,then1 instead of sinking its valley vertically downward into the quartzite1 the stream would have shifted its channel down the slope of the range along the junction of the softer and harder rock 7,fig4 #be74 ,such changes occasioned by the nature and position of the rock concerned1 are known as adjustments4 ,illustration3 ,fig4 #be4--;,diagram illustrating the hypothetical case of a stream working down the slope of the quartzite range4 ,the successive sections of the valley are suggested by the lines ae1 be1 ce and de4 ,streams which crossed the quartzite ridges on the overlying strata might have held their courses even after their valleys were lowered to the level of the quartzite4 ,such streams would have developed narrows at the crossing of the quartzite4 ,in so far as there were passes in the quartzite range before the deposition of the ,paleozoic beds1 they were filled during the long period of sedimentation1 to be again cleared out during the subsequent period of erosion4 ,the gap in the ,south range now occupied by the lake was a narrows in a valley which existed1 though perhaps not to its present depth1 before the ,potsdam sandstone was deposited4 ,it was filled when the sediments of that formation were laid down1 to be again opened1 and perhaps deepened1 in the period of erosion which followed the deposition of the ,paleozoic series4 ,during the earliest period of erosion of which there is positive evidence1 after the uplift of the ,paleozoic beds1 the softer formations about the quartzite were worn down to a level #djj or #ejj feet below the crests of the ,south quartzite range4 ,at this lower level1 an approximate plain1 a peneplain1 was developed1 the level of which is shown by numerous hills1 the summits of which now reach an elevation of from #a1jjj to #a1ajj feet above the sea4 ,at the time of its development1 this peneplain was but little above sea level1 for this is the only elevation at which running water can develop such a plain4 ,above the general level of this plain rose the quartzite ranges as elongate monadnocks1 the highest parts of which were fully #ejj feet above the plain4 ,a few other points in the vicinity failed to be reduced to the level of the peneplain4 ,the #a1cbj foot hill 7d1 ,plate ,,xxxvii71 one and one-half miles southeast of the ,lower narrows1 and ,gibraltar ,rock 7e1 same ,plate71 two miles southeast of ,merrimac1 rose as prominences above it4 ,it is possible that these crests are remnants of a base-level plain older than that referred to above4 ,if while the quartzite remained much as now1 the valleys in the sandstone below #a1jjj or #a1ajj feet were filled1 the result would correspond in a general way to the surface which existed in this region when the first distinctly recognizable cycle of erosion was brought to a close4 ,above the undulating plain developed in the sandstone and limestone1 the main quartzite ridge would have risen as a conspicuous ridge #djj to #ejj feet4 ,this cycle had not been completed1 that is1 the work of base-leveling had not been altogether accomplished1 when the peneplain was elevated1 and the cycle1 though still incomplete1 brought to a close4 ,by the uplift1 the streams were rejuvenated1 and sunk their valleys into the elevated peneplain4 ,thus a new cycle of erosion was begun1 and the uplifted peneplain was dissected by the quickened streams which sank their valleys promptly into the slightly resistant sandstone4 ,at their new base-level1 they ultimately developed new flats4 ,this cycle of erosion appears to have advanced no farther than to the development of wide flats along the principal streams1 such as the ,wisconsin and the ,baraboo1 and narrow ones along the subordinate water courses1 when it was interrupted4 ,along the main streams the new flats were at a level which is now from #hjj to #ijj feet above the sea1 and #gjj to #hjj feet below the ,south quartzite range4 ,it was at this time that the plains about ,camp ,douglas and ,necedah1 already referred to1 were developed4 ,during this second incomplete cycle1 the quartzite ranges1 resisting erosion1 came to stand up still more prominently than during the first4 ,the interruption of this cycle was caused by the advent of the glacial period which disturbed the normal course of erosion4 ,this period was accompanied and followed by slight changes of level which also had their influence on the streams4 ,the consideration of the effects of glaciation and of subsequent river erosion are postponed1 but it may be stated that within the area which was glaciated the post-glacial streams have been largely occupied in removing the drift deposited by the ice from the preglacial valleys1 or in cutting new valleys in the drift4 ,the streams outside the area of glaciation were less seriously disturbed4 ,at levels other than those indicated1 partial base-levels are suggested1 and although less well marked in this region1 they might1 in the study of a broader area1 bring out a much more complicated erosion history4 ,as already suggested1 one cycle may have preceded that the remnants of which now stand #a1jjj-a1ajj feet above sea level1 and another may have intervened between this and that marked by the #hjj to #ijj foot level4 ,from the foregoing it is clear that the topography of the region is1 on the whole1 an erosion topography1 save for certain details in its eastern portion4 ,the valleys differ in form and in size1 with their age1 and with the nature of the material in which they are cut2 while the hills and ridges differ with varying relations to the streams1 and with the nature of the material of which they are composed4 ,striking ,scenic ,features4 ,in a region so devoid of striking scenery as the central portion of the ,mississippi basin1 topographic features which would be passed without special notice in regions of greater relief1 become the objects of interest4 ,but in south central ,wisconsin there are various features which would attract attention in any region where the scenery is not mountainous4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,xxi4 ,cleopatra's ,needle4 ,west ,bluff of ,devil's ,lake4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,xxii4 ,turk's ,head4 ,west ,bluff of ,devil's ,lake4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,xxiii4 ,devil's ,doorway4 ,east of ,devil's ,lake4 ,on the bluffs at ,devil's lake there are many minor features which are sure to attract the attention of visitors4 ,such are ,cleopatra's ,needle 7,plate ,,xxi71 ,turk's ,head 7,plate ,,xxii71 and the ,devil's ,doorway 7,plate ,,xxiii74 ,these particular forms have resulted from the peculiar weathering of the quartzite4 ,the rock is affected by several systems of vertical or nearly vertical joint planes 7cracks71 which divide the whole formation into a series of vertical columns4 ,there are also horizontal and oblique planes of cleavage dividing the columns1 so that the great quartzite pile may be said to be made up of a series of blocks1 which are generally in contact with one another4 ,the isolated pillars and columns which have received special names have been left as they now stand by the falling away of the blocks which once surrounded them4 ,they themselves must soon follow4 ,the great talus slopes at the base of the bluffs1 such as those on the west side of the lake and on the ,east bluff near its southeast corner1 ,plate ,,xxiv1 are silent witnesses of the extent to which this process has already gone4 ,the blocks of rock of which they are composed have been loosened by freezing water1 by the roots of trees1 and by expansion and contraction due to changing temperature1 and have fallen from their former positions to those they now occupy4 ,their descent1 effected by gravity directly1 is1 it will be noted1 the first step in their journey to the sea1 the final resting place of all products of land degradation4 ,the ,baraboo bluffs4--,nowhere in southern ,wisconsin1 or indeed in a large area adjacent to it1 are there elevations which so nearly approach mountains as the ranges of quartzite in the vicinity of ,baraboo and ,devil's lake4 ,so much has already been said of their history that there is need for little further description4 ,plate ,,iv gives some idea of the appearance of the ranges4 ,the history of the ranges1 already outlined1 involves the following stages3 7#a7 ,the deposition of the sands in ,huronian time2 7#b7 the change of the sand to sandstone and the sandstone to quartzite2 7#c7 the uplift and deformation of the beds2 7#d7 igneous intrusions1 faulting1 crushing1 and shoaring1 with the development of schists accompanying the deformation2 7#e7 a prolonged period of erosion during which the folds of quartzite were largely worn away1 though considerable ridges1 the ,huronian mountains of early ,cambrian times1 still remained high above their surroundings2 7#f7 the submergence of the region1 finally involving even the crests of the ridges of quartzite2 7#g7 a protracted period of deposition during which the ,potsdam sandstone and several later ,paleozoic formations were laid down about1 and finally over1 the quartzite1 burying the mountainous ridges2 7#h7 the elevation of the ,paleozoic sea-bottom1 converting it into land2 7#i7 a long period of erosion1 during which the upper ,paleozoic beds were removed1 and the quartzite re-discovered4 ,being much harder than the ,paleozoic rocks1 the quartzite ridges again came to stand out as prominent ridges1 as the surrounding beds of relatively slight resistance were worn away4 ,they are resurrected mountains1 though not with the full height which they had in pre-,cambrian time1 for they are still partially buried by younger beds4 ,the narrows in the quartzite4--,there are four narrows or passes in the quartzite ridges1 all of which are rather striking features4 ,one of them is in the ,south range1 one in the ,north range near its eastern end1 while the others are in an isolated area of quartzite at ,ablemans which is really a continuation of the ,north range4 ,two of these narrows are occupied by the ,baraboo river1 one by ,narrows creek1 and the fourth by ,devil's lake4 ,from ,ablemans to a point several miles east of ,baraboo1 the ,baraboo river flows through a capacious valley4 ,where it crosses the ,north range1 six miles or more north of east of ,baraboo1 the broad valley is abruptly constricted to a narrow pass with precipitous sides1 about #ejj feet high 7c1 ,plate ,,xxxvii74 ,this constriction is the ,lower narrows1 conspicuous from many points on the ,south range1 and from the plains to the north4 ,beyond the quartzite1 the valley again opens out into a broad flat4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,xxiv4 ,talus slope on the east bluff of ,devil's lake4 ,seen from a distance1 the narrows has the appearance of an abrupt notch in the high ridge 7,plate ,,iv74 ,seen at closer range1 the gap is still more impressive4 ,it is in striking contrast with the other narrows in that there are no talus accumulations at the bases of the steep slopes1 and in that the slopes are relatively smooth and altogether free from the curious details of sculpture seen in the other gaps where the slopes are equally steep4 ,the ,upper narrows of the ,baraboo at ,ablemans 7b1 ,plate ,,ii7 is in some ways similar to the ,lower1 though less conspicuous because less deep4 ,its slopes are more rugged1 and piles of talus lie at their bases as at ,devil's lake4 ,this narrows also differs from the ,lower in that the quartzite on one side is covered with ,potsdam conglomerate1 which overlies the truncated edges of the vertical layers of quartzite with unconformable contact4 ,so clear an example of unconformity is not often seen4 ,potsdam sandstone is also seen to rest against the quartzite on either side of the narrows 7,fig4 #bf71 thus emphasizing the unconformity4 ,the beauty and interest of this narrows is enhanced by the quartzite breccia 7 which appears on its walls4 ,illustration3 ,fig4 #bf4--;,a generalized diagrammatic cross-section at the ,upper narrows1 to show the relation of the sandstone to the quartzite4 ,one and one-half miles west of ,ablemans 7a1 ,plate ,,ii7 is the third pass in the north quartzite ridge4 ,this pass is narrower than the others1 and is occupied by ,narrows creek4 ,its walls are nearly vertical and possess the same rugged beauty as those at ,ablemans4 ,as at the ,upper narrows1 the beds of quartzite here are essentially vertical4 ,they are indeed the continuation of the beds exposed at that place4 ,the fourth narrows is across the ,south range 7i1 ,plate ,,ii74 ,it is not now occupied by a stream1 though like the others it was cut by a stream1 which was afterwards shut out from it4 ,because of its depth1 #fjj feet1 and the ruggedness of its slopes1 and because of its occupancy by the lake1 this pass is the center of interest for the whole region4 ,so much has already been said concerning it in other portions of this report that further description is here omitted4 ,the manner in which the pass was robbed of its stream will be discussed later4 ,the history of these several narrows1 up to the time of the glacial period may now be summarized4 ,since remnants of ,potsdam sandstone are found in some of them1 it is clear that they existed in pre-,cambrian time1#f and there is no reason to doubt that they are the work of the streams of those ancient days1 working as streams now work4 ,following the pre-,cambrian period of erosion during which the notches were cut1 came the submergence of the region1 and the gaps were filled with sand and gravel1 and finally the ridges themselves were buried4 ,uplift and a second period of erosion followed1 during which the quartzite ranges were again exposed by the removal of the beds which overlay them1 and the narrows cleaned out and deepened1 and again occupied by streams4 ,this condition of things lasted up to the time when the ice invaded the region4 #f ,it is not here asserted that these notches were as deep as now1 in pre-,cambrian time4 ,it is1 however1 certain that the quartzite was deeply eroded1 previous to the deposition of the ,potsdam sandstone4 ,glens4--,no enumeration of the special scenic features of this region would be complete without mention of ,parfrey's and ,dorward's glens 7a and b1 ,plate ,,xxxvii1 and ,plate ,,xxv74 ,attention has already been directed to them as illustrations of young valleys1 and as places where the ,potsdam conglomerate is well shown1 but they are attractive from the scenic point of view4 ,their frequent mention in earlier parts of this report makes further reference to them at this point unnecessary4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,xxv4 ,in ,dorward's ,glen4 ,the basal conglomerate of the ,potsdam formation is shown at the lower right-hand corner1 and is overlain by sandstone4 7,photograph furnished by ,mr4 ,wilfred ,dorward74 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,xxvi4 ,natural bridge near ,denzer4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,xxvii4 ,navy ,yard4 ,dalles of the ,wisconsin4 ,pine ,hollow 7k1 ,plate ,,ii7 is another attractive gorge on the south flank of the greater quartzite range4 ,the rock at this point is especially well exposed4 ,this gorge is beyond the drift-covered portion of the range1 and therefore dates from the pre-glacial time4 ,the ,pewit's nest1 about three miles southwest of ,baraboo 7m1 ,plate ,,ii71 is another point of interest4 ,above the nest1 ,skillett creek flows through a narrow and picturesque gorge in the ,potsdam sandstone4 ,the origin of this gorge is explained elsewhere4 ,natural ,bridge4--,about two miles north and a little west of the village of ,denzer 7,sec4 #ag1 ,t4 #aj ,n41 ,r4 #e ,e471 is a small natural bridge1 which has resulted from the unequal weathering of the sandstone 7see ,plate ,,xxvi74 ,the bridge is curious1 rather than beautiful or impressive4 ,the ,dalles of the ,wisconsin4--,the dalles is the term applied to a narrow canyon-like stretch of the ,wisconsin valley seven miles in length1 near ,kilbourn ,city 7see frontispiece74 ,the depth of the gorge is from #ej to #ajj feet4 ,the part above the bridge at ,kilbourn ,city is the ,upper dalles2 that below1 the ,lower dalles4 ,within this stretch of the valley are perhaps the most picturesque features of the region4 ,the sides of the gorge are nearly vertical much of the way1 and at many points are so steep on both sides that landing would be impossible4 ,between these sandstone walls flows the deep and swift ,wisconsin river4 ,such a rock gorge is in itself a thing of beauty1 but in the dalles there are many minor features which enhance the charm of the whole4 ,one of the features which deserves especial mention is the peculiar crenate form of the walls at the banks of the river4 ,this is perhaps best seen in that part of the dalles known as the ,navy ,yard4 ,plate ,,xxvii4 ,the sandstone is affected by a series of vertical cracks or joints4 ,from weathering1 the rock along these joints becomes softened1 and the running water wears the softened rock at the joint planes more readily than other parts of its bank1 and so develops a reentrant at these points4 ,rain water descending to the river finds and follows the joint planes1 and thus widens the cracks4 ,as a result of stream and rain and weathering1 deep reentrant angles are produced4 ,the projections between are rounded off so that the banks of the stream have assumed the crenate form shown in ,plate ,,xxviii1 and ,frontispiece4 ,when this process of weathering at the joints is carried sufficiently far1 columns of rock become isolated1 and stand out on the river bluffs as chimneys 7,plate ,,xxviii74 ,at a still later stage of development1 decay of the rock along the joint planes may leave a large mass of rock completely isolated4 ,steamboat rock 7,plate ,,xii7 and ,sugar bowl 7,plate ,,xxix7 are examples of islands thus formed4 ,the walls of sandstone weather in a peculiar manner at some points in the ,lower dalles1 as shown on ,plate ,,xxx4 ,the little ridges stand out because they are harder and resist weathering better than the other parts4 ,this is due in part at least to the presence of iron in the more resistant portions1 cementing them more firmly4 ,in the process of segregation1 cementing materials are often distributed unequally4 ,the effect of differences in hardness on erosion is also shown on a larger scale and in other ways4 ,perhaps the most striking illustration is ,stand rock 7,plate ,,xxxi71 but most of the innumerable and picturesque irregularities on the rock walls are to be accounted for by such differences4 ,minor valleys tributary to the ,wisconsin1 such as ,witch's gulch and ,cold ,water canyon deserve mention1 both because of their beauty1 and because they illustrate a type of erosion at an early stage of valley development4 ,in character they are comparable to the larger gorge to which they are tributary4 ,in the downward cutting1 which far exceeds the side wear in these tributary canyons1 the water has excavated large bowl or jug-like forms4 ,in ,witch's gulch such forms are now being excavated4 ,they are developed just below falls1 where the water carrying debris1 eddies1 and the jugs or pot-holes are the result of the wear effected by the eddies4 ,the ,devil's jug and many similar hollows are thus explained4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,xxviii4 ,chimney ,rock4 ,dalles of the ,wisconsin4 ,cross-bedding well shown in foreground near bottom4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,xxix4 ,an ,island in the ,lower ,dalles4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,xxx4 ,view in lower ,dalles showing peculiar honeycomb weathering4 ,the mounds and castle rocks4--,in the vicinity of ,camp ,douglas and over a large area to the east1 are still other striking topographic forms1 which owe their origin to different conditions1 though they were fashioned by the same forces4 ,here there are many tower or castle rocks1 which rise to heights varying from #ge to #aij feet above the surrounding plain4 ,they are remnants of beds which were once continuous over the low lands above which the hills now rise4 ,in ,plates ,,xvii and ,,xviii the general character of these hills is shown4 ,the rock of which they are composed is ,potsdam sandstone1 the same formation which underlies most of the area about ,baraboo4 ,the effect of the vertical joints and of horizontal layers of unequal hardness is well shown4 ,rains1 winds1 frosts1 and roots are still working to compass the destruction of these picturesque hills1 and the talus of sand bordering the castle is a reminder of the fate which awaits them4 ,these hills are the more conspicuous and the more instructive since the plain out of which they rise is so flat4 ,it is indeed one of the best examples of a base-level plain to be found on the continent4 ,the crests of these hills reach an elevation of between #a1jjj and #a1ajj feet4 ,they appear to correspond with the level of the first peneplain recognized in the ,devil's lake region4 ,it was in the second cycle of erosion1 when their surroundings were brought down to the new base-level1 that these hills were left4 ,west of ,camp ,douglas1 there are still higher elevations1 which seem to match ,gibraltar rock4 ,the ,friendship mounds north of ,kilbourn ,city1 the castellated hills a few miles northwest of the same place1 and ,petenwell peak on the banks of the ,wisconsin 7,plate ,,xxxii71 are further examples of the same class of hills4 ,all are of ,potsdam sandstone4 ,in addition to the castle rocks and base-level plain about ,camp ,douglas1 other features should be mentioned4 ,no other portion of the area touched upon in this report affords such fine examples of the different types of erosion topography4 ,in the base-level plain are found old-age valleys1 broad and shallow1 with the stream meandering in a wide flood-plain4 ,traveling up such a valley1 the topography becomes younger and younger1 and the various stages mentioned earlier in the text1 and suggested in ,plate ,,xix1 ,figs4 #a and #b1 and ,plate ,,xx1 ,fig4 #a1 are here illustrated4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,xxxi4 ,stand ,rock4 ,upper end of the ,upper ,dalles4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,xxxii4 ,petenwell ,peak4 ,,chapter ,v4 ,,the ,,glacial ,,period4 ,the eastern part of the area with which this report deals1 is covered with a mantle of drift which1 as already pointed out1 has greatly modified the details of its topography4 ,to the consideration of the drift and its history attention is now turned4 ,the drift4--,the drift consists of a body of clay1 sand1 gravel and bowlders1 spread out as a cover of unequal thickness over the rock formations beneath4 ,these various classes of material may be confusedly commingled1 or they may be more or less distinctly separated from one another4 ,when commingled1 all may be in approximately equal proportions1 or any one may predominate over any or all the others to any extent4 ,it was long since recognized that the materials of the drift did not originate where they now lie1 and that1 in consequence1 they sustain no genetic relationship to the strata on which they rest4 ,long before the drift received any special attention from geologists1 it was well known that it had been transported from some other locality to that where it now occurs4 ,the early conception was that it had been drifted into its present position from some outside source by water4 ,it was this conception of its origin which gave it the name of drift4 ,it is now known that the drift was deposited by glacier ice and the waters which arose from its melting1 but the old name is still retained4 ,clearly to understand the origin of the drift1 and the method by which it attained its present distribution1 it may be well to consider some elementary facts and principles concerning climate and its effects1 even at the risk of repeating what is already familiar4 ,snow fields and ice sheets4--,the temperature and the snowfall of a region may stand in such a relation to each other that the summer's heat may barely suffice to melt the winter's snow4 ,if under these circumstances the annual temperature were to be reduced1 or the fall of snow increased1 the summer's heat would fail to melt all the winter's snow1 and some portion of it would endure through the summer1 and through successive summers1 constituting a perennial snow-field4 ,were this process once inaugurated1 the depth of the snow would increase from year to year4 ,the area of the snow-field would be extended at the same time1 since the snow-field would so far reduce the surrounding temperature as to increase the proportion of the annual precipitation which fell as snow4 ,in the course of time1 and under favorable conditions1 the area of the snow-field would attain great dimensions1 and the depth of the snow would become very great4 ,as in the case of existing snow fields the lower part of the snow mass would eventually be converted into ice4 ,several factors would conspire to this end4 #a4 ,the pressure of the overlying snow would tend to compress the lower portion1 and snow rendered sufficiently compact by compression would be regarded as ice4 #b4 ,water arising from the melting of the surface snow by the sun's heat1 would percolate through the superficial layers of snow1 and1 freezing below1 take the form of ice4 #c4 ,on standing1 even without pressure or partial melting1 snow appears to undergo changes of crystallization which render it more compact4 ,in these and perhaps other ways1 a snow-field becomes an ice-field1 the snow being restricted to its surface4 ,eventually the increase in the depth of the snow and ice in a snow-field will give rise to new phenomena4 ,let a snow and ice field be assumed in which the depth of snow and ice is greatest at the center1 with diminution toward its edges4 ,the field of snow1 if resting on a level base1 would have some such cross-section as that represented in the diagram1 ,fig4 #bg4 ,when the thickness of the ice has become considerable1 it is evident that the pressure upon its lower and marginal parts will be great4 ,we are wont to think of ice as a brittle solid4 ,if in its place there were some plastic substance which would yield to pressure1 the weight of the ice would cause the marginal parts to extend themselves in all directions by a sort of flowing motion4 ,illustration3 ,fig4 #bg4--;,diagrammatic cross-section of a field of ice and snow 7c7 resting on a level base ,a-,b4 ,under great pressure1 many substances which otherwise appear to be solid1 exhibit the characteristics of plastic bodies4 ,among the substances exhibiting this property1 ice is perhaps best known4 ,brittle and resistant as it seems1 it may yet be molded into almost any desirable form if subjected to sufficient pressure1 steadily applied through long intervals of time4 ,the changes of form thus produced in ice are brought about without visible fracture4 ,concerning the exact nature of the movement1 physicists are not agreed2 but the result appears to be essentially such as would be brought about if the ice were capable of flowing1 with extreme slowness1 under great pressure continuously applied4 ,in the assumed ice-field1 there are the conditions for great pressure and for its continuous application4 ,if the ice be capable of moving as a plastic body1 the weight of the ice would induce gradual movement outward from the center of the field1 so that the area surrounding the region where the snow accumulated would gradually be encroached upon by the spreading of the ice4 ,observation shows that this is what takes place in every snow-field of sufficient depth4 ,motion thus brought about is glacier motion1 and ice thus moving is glacier ice4 ,once in motion1 two factors would determine the limit to which the ice would extend itself3 7#a7 the rate at which it advances2 and 7#b7 the rate at which the advancing edge is wasted4 ,the rate of advance would depend upon several conditions1 one of which1 in all cases1 would be the pressure of the ice which started and which perpetuates the motion4 ,if the pressure be increased the ice will advance more rapidly1 and if it advance more rapidly1 it will advance farther before it is melted4 ,other things remaining constant1 therefore1 increase of pressure will cause the ice-sheet to extend itself farther from the center of motion4 ,increase of snowfall will increase the pressure of the snow and ice field by increasing its mass4 ,if1 therefore1 the precipitation over a given snow-field be increased for a period of years1 the ice-sheet's marginal motion will be accelerated1 and its area enlarged4 ,a decrease of precipitation1 taken in connection with unchanged wastage would decrease the pressure of the ice and retard its movement4 ,if1 while the rate of advance diminished1 the rate of wastage remained constant1 the edge of the ice would recede1 and the snow and ice field be contracted4 ,the rate at which the edge of the advancing ice is wasted depends largely on the climate4 ,if1 while the rate of advance remains constant1 the climate becomes warmer1 melting will be more rapid1 and the ratio between melting and advance will be increased4 ,the edge of the ice will therefore recede4 ,the same result will follow1 if1 while temperature remains constant1 the atmosphere becomes drier1 since this will increase wastage by evaporation4 ,were the climate to become warmer and drier at the same time1 the rate of recession of the ice would be greater than if but one of these changes occurred4 ,if1 on the other hand1 the temperature over and about the ice field be lowered1 melting will be diminished1 and if the rate of movement be constant1 the edge of the ice will advance farther than under the earlier conditions of temperature1 since it has more time to advance before it is melted4 ,an increase in the humidity of the atmosphere1 while the temperature remains constant1 will produce the same result1 since increased humidity of the atmosphere diminishes evaporation4 ,a decrease of temperature1 decreasing the melting1 and an increase of humidity1 decreasing the evaporation1 would cause the ice to advance farther than either change alone1 since both changes decrease the wastage4 ,if1 at the same time that conditions so change as to increase the rate of movement of the ice1 climatic conditions so change as to reduce the rate of waste1 the advance of the ice before it is melted will be greater than where only one set of conditions is altered4 ,if1 instead of favoring advance1 the two series of conditions conspire to cause the ice to recede1 the recession will likewise be greater than when but one set of conditions is favorable thereto4 ,greenland affords an example of the conditions here described4 ,a large part of the half million or more square miles which this body of land is estimated to contain1 is covered by a vast sheet of snow and ice1 thousands of feet in thickness4 ,in this field of snow and ice1 there is continuous though slow movement4 ,the ice creeps slowly toward the borders of the island1 advancing until it reaches a position where the climate is such as to waste 7melt and evaporate7 it as rapidly as it advances4 ,the edge of the ice does not remain fixed in position4 ,there is reason to believe that it alternately advances and retreats as the ratio between movement and waste increases or decreases4 ,these oscillations in position are doubtless connected with climatic changes4 ,when the ice edge retreats1 it may be because the waste is increased1 or because the snowfall is decreased1 or both4 ,in any case1 when the ice edge recedes from the coast1 it tends to recede until its edge reaches a position where the melting is less rapid than in its former position1 and where the advance is counterbalanced by the waste4 ,this represents a condition of equilibrium so far as the edge of the ice is concerned1 and here the edge of the ice would remain so long as the conditions were unchanged4 ,when for a period of years the rate of melting of the ice is diminished1 or the snowfall increased1 or both1 the ice edge advances to a new line where melting is more rapid than at its former edge4 ,the edge of the ice would tend to reach a position where waste and advance balance4 ,here its advance would cease1 and here its edge would remain so long as climatic conditions were unchanged4 ,if the conditions determining melting and flowage be continually changing1 the ice edge will not find a position of equilibrium1 but will advance when the conditions are favorable for advance1 and retreat when the conditions are reversed4 ,not only the edge of the ice in ,greenland1 but the ends of existing mountain glaciers as well1 are subject to fluctuation1 and are delicate indices of variations in the climate of the regions where they occur4 ,the ,north ,american ice sheet4--,in an area north of the eastern part of the ,united ,states and in another west of ,hudson ,bay it is believed that ice sheets similar to that which now covers ,greenland began to accumulate at the beginning of the glacial period4 ,from these areas as centers1 the ice spread in all directions1 partly as the result of accumulation1 and partly as the result of movement induced by the weight of the ice itself4 ,the ice sheets spreading from these centers came together south of ,hudson's bay1 and invaded the territory of the ,united ,states as a single sheet1 which1 at the time of its greatest development1 covered a large part of our country 7,plate ,,xxxiii71 its area being known by the extent of the drift which it left behind when it was melted4 ,in the east1 it buried the whole of ,new ,england1 most of ,new ,york1 and the northern parts of ,new ,jersey and ,pennsylvania4 ,farther west1 the southern margin of the ice crossed the ,ohio river in the vicinity of ,cincinnati1 and pushed out over the uplands a few miles south of the river4 ,in ,indiana1 except at the extreme east1 its margin fell considerably short of the ,ohio2 in ,illinois it reached well toward that river1 attaining here its most southerly latitude4 ,west of the ,mississippi1 the line which marks the limit of its advance curves to the northward1 and follows1 in a general way1 the course of the ,missouri river4 ,the total area of the ,north ,american ice sheet1 at the time of its maximum development1 has been estimated to have been about #d1jjj1jjj square miles1 or about ten times the estimated area of the present ice-field of ,greenland4 ,within the general area covered by the ice1 there is an area of several thousand square miles1 mainly in southwestern ,wisconsin1 where there is no drift4 ,the ice1 for some reason1 failed to cover this driftless area though it overwhelmed the territory on all sides4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,xxxiii4 ,the ,north ,american ,ice ,sheet1 at the time of maximum development4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,xxxiv4 ,view from the north of the ,owl's ,head1 a hill two miles north of east of ,merrimac1 which has been shaped by the ice4 ,the side to the left is the stone side4 ,plate ,,ii shows the limit of ice advance in the area here described4 ,the region may have been affected by the ice of more than one glacial epoch1 but the chief results now observable were effected during the last1 and the others need not be considered4 ,the ,work of ,glacier ,ice4 ,as the edge of an ice sheet1 or as the end of a glacier1 retreats1 the land which it has previously covered is laid bare1 and the effects which the passage of the ice produced may be seen4 ,in some cases one may actually go back a short distance beneath the ice now in motion1 and see its mode of work and the results it is effecting4 ,the beds of living glaciers1 and the beds which glaciers have recently abandoned1 are found to present identical features4 ,because of their greater accessibility1 the latter offer the better facilities for determining the effects of glaciation4 ,the conspicuous phenomena of abandoned glacier beds fall into two classes1 7#a7 those which pertain to the bed rock over which the ice moved1 and 7#b7 those which pertain to the drift left by the ice4 ,erosive work of the ice4--,effect on topography4--,the leading features of the rock bed over which glacier ice has moved1 are easily recognized4 ,its surface is generally smoothed and polished1 and frequently marked by lines 7striae7 or grooves1 parallel to one another4 ,an examination of the bottom of an active glacier discloses the method by which the polishing and scoring are accomplished4 ,the lower surface of the ice is thickly set with a quantity of clay1 sand1 and stony material of various grades of coarseness4 ,these earthy and stony materials in the base of the ice are the tools with which it works4 ,thus armed1 the glacier ice moves slowly forward1 resting down upon the surfaces over which it passes with the whole weight of its mass1 and the grinding action between the stony layer at the base of the ice and the rock bed over which it moves1 is effective4 ,if the material in the bottom of the ice be fine1 like clay1 the rock bed is polished4 ,if coarser materials1 harder than the bed-rock1 be mingled with the fine1 the rock bed of the glacier will be scratched as well as polished4 ,if there are bowlders in the bottom of the ice they may cut grooves or gorges in the underlying rock4 ,the grooves may subsequently be polished by the passage over and through them of ice carrying clay or other fine1 earthy matter4 ,all these phases of rock wear may be seen about the termini of receding glaciers1 on territory which they have but recently abandoned4 ,there can thus be no possible doubt as to the origin of the polishing1 planing and scoring4 ,there are other peculiarities1 less easily defined1 which characterize the surface of glacier beds4 ,the wear effected is not confined to the mere marking of the surface over which it passes4 ,if prominences of rock exist in its path1 as is often the case1 they oppose the movement of the ice1 and receive a corresponding measure of abrasion from it4 ,if they be sufficiently resistant they may force the ice to yield by passing over or around them2 but if they be weak1 they are likely to be destroyed4 ,as the ice of the ,north ,american ice sheet advanced1 seemingly more rigid when it encountered yielding bodies1 and more yielding when it encountered resistant ones1 it denuded the surface of its loose and movable materials1 and carried them forward4 ,this accumulation of earthy and stony debris in the bottom of the ice1 gave it a rough and grinding lower surface1 which enabled it to abrade the land over which it passed much more effectively than ice alone could have done4 ,every hill and every mound which the ice encountered contested its advance4 ,every sufficiently resistant elevation compelled the ice to pass around or over it2 but even in these cases the ice left its marks upon the surface to which it yielded4 ,the powerful pressure of pure ice1 which is relatively soft1 upon firm hills of rock1 which are relatively hard1 would effect little4 ,the hills would wear the ice1 but the effect of the ice on the hills would be slight4 ,but where the ice is supplied with earthy and stony material derived from the rock itself1 the case is different4 ,under these conditions1 the ice1 yielding only under great pressure and as little as may be1 rubs its rock-shod base over every opposing surface1 and with greatest severity where it meets with greatest resistance4 ,its action may be compared to that of a huge flexible-rasp fitting down snugly over hills and valleys alike1 and working under enormous pressure4 ,the abrasion effected by a moving body of ice under such conditions would be great4 ,every inch of ice advance would be likely to be attended by loss to the surface of any obstacle over or around which it is compelled to move4 ,the sharp summits of the hills1 and all the angular rugosities of their surfaces would be filed off1 and the hills smoothed down to such forms as will offer progressively less and less resistance4 ,if the process of abrasion be continued long enough1 the forms1 even of the large hills1 may be greatly altered1 and their dimensions greatly reduced4 ,among the results of ice wear1 therefore1 will be a lowering of the hills1 and a smoothing and softening of their contours1 while their surfaces will bear the marks of the tools which fashioned them1 and will be polished1 striated or grooved1 according to the nature of the material which the ice pressed down upon them during its passage4 ,figs4 #bh and #bi show the topographic effects which ice is likely to produce by erosion4 ,plate ,,xxxiv is a hill two miles northeast of ,merrimac1 which shows how perfectly the wear actually performed corresponds to that which might be inferred4 ,illustration3 ,fig4 #bh4--;,a hill before the ice passes over it4 ,a rock hill was sometimes left without covering of drift after having been severely worn by the ice4 ,such a hill is known as a roche moutonnee4 ,an example of this type of hill occurs three miles north of east of ,baraboo at the point marked z on ,plate ,,xxxvii4 ,this hill1 composed of quartzite1 is less symmetrical than those shown in ,figs4 #bh and #bi4 ,its whole surface1 not its stoss side only1 has been smoothed and polished by the ice4 ,this hill is the most accessible1 the most easily designated1 and1 on the whole1 the best example of a roche moutonnee in the region1 though many other hills show something of the same form4 ,illustration3 ,fig4 #bi4--,the same hill after it has been eroded by the ice4 ,a the stoss side4 ,b the lee side4 ,it was not the hills alone which the moving ice affected4 ,where it encountered valleys in its course they likewise suffered modification4 ,where the course of a valley was parallel to the direction of the ice movement1 the ice moved through it4 ,the depth of moving ice is one of the determinants of its velocity1 and because of the greater depth of ice in valleys1 its motion here was more rapid than on the uplands above1 and its abrading action more powerful4 ,under these conditions the valleys were deepened and widened4 ,where the courses of the valleys were transverse to the direction of ice movement1 the case was different4 ,the ice was too viscous to span the valleys1 and therefore filled them4 ,in this case it is evident that the greater depth of the ice in the valley will not accelerate its motion1 since the ice in the valley-trough and that above it are in a measure opposed4 ,if left to itself1 the ice in the valley would tend to flow in the direction of the axis of the valley4 ,but in the case under consideration1 the ice which lies above the valley depression is in motion at right angles to the axis of the valley4 ,under these circumstances three cases might arise3 7#a7 ,if the movement of the ice sheet over the valley were able to push the valley ice up the farther slope1 and out on the opposite highland1 this work would retard the movement of the upper ice1 since the resistance to movement would be great4 ,in this case1 the thickness of the ice is not directly and simply a determinant of its velocity4 ,under these conditions the bottom of the valley would not suffer great erosion1 since ice did not move along it2 but that slope of the valley against which the ice movement was projected would suffer great wear 7,fig4 #cj74 ,the valley would therefore be widened1 and the slope suffering greatest wear would be reduced to a lower angle4 ,shallow valleys1 and those possessing gentle slopes1 favor this phase of ice movement and valley wear4 ,illustration3 ,fig4 #cj4--;,diagram showing effect on valley of ice moving transversely across it4 7#b7 ,the ice in the valley might become stationary1 in which case it might serve as a bridge for the upper ice to cross on 7,fig4 #ca74 ,in this case also the total thickness of ice will not be a determinant of its velocity1 for it is the thickness of the moving ice only1 which influences the velocity4 ,in this case the valley would not suffer much wear1 so long as this condition of things continued4 ,valleys which have great depth relative to the thickness of the ice1 and valleys whose slopes are steep1 favor this phase of movement4 7#c7 ,in valleys whose courses are transverse to the direction of ice movement1 transverse currents of ice may exist1 following the direction of the valleys4 ,if the thickness of the ice be much greater than the depth of the valley1 if the valley be capacious1 and if one end of it be open and much lower than the other1 the ice filling it may move along its axis1 while the upper ice continues in its original course at right angles to the valley4 ,in this case the valley would be deepened and widened1 but this effect would be due to the movement along its course1 rather than to that transverse to it4 ,illustration3 ,fig4 #ca--;,diagram to illustrate case where ice fills a valley 7,c7 and the upper ice then moves on over the filling4 ,if the course of a valley were oblique to the direction of ice movement1 its effect on the movement of ice would be intermediate between that of valleys parallel to the direction of movement1 and those at right angles to it4 ,it follows from the foregoing that the corrasive effects of ice upon the surface over which it passed1 were locally dependent on pre-existent topography1 and its relation to the direction of ice movement4 ,in general1 the effort was to cut down prominences1 thus tending to level the surface4 ,but when it encountered valleys parallel to its movement they were deepened1 thus locally increasing relief4 ,whether the reduction of the hills exceeded the deepening of the valleys1 or whether the reverse was true1 so far as corrasion alone is concerned1 is uncertain4 ,but whatever the effect of the erosive effect of ice action upon the total amount of relief1 the effect upon the contours was to make them more gentle4 ,not only were the sharp hills rounded off1 but even the valleys which were deepened were widened as well1 and in the process their slopes became more gentle4 ,a river-erosion topography1 modified by the wearing 7not the depositing7 action of the ice1 would be notably different from the original1 by reason of its gentler slopes and softer contours 7,figs4 #bh and #bi74 ,deposition by the ice4 ,effect on topography4--,on melting1 glacier ice leaves its bed covered with the debris which it gathered during its movement4 ,had this debris been equally distributed on and in and beneath the ice during its movement1 and had the conditions of deposition been everywhere the same1 the drift would constitute a mantle of uniform thickness over the underlying rock4 ,such a mantle of drift would not greatly alter the topography2 it would simply raise the surface by an amount equal to the thickness of the drift1 leaving elevations and depressions of the same magnitude as before1 and sustaining the same relations to one another4 ,but the drift carried by the ice1 in whatever position1 was not equally distributed during transportation1 and the conditions under which it was deposited were not uniform1 so that it produced more or less notable changes in the topography of the surface on which it was deposited4 ,the unequal distribution of the drift is readily understood4 ,the larger part of the drift transported by the ice was carried in its basal portion2 but since the surface over which the ice passed was variable1 it yielded a variable amount of debris to the ice4 ,where it was hilly1 the friction between it and the ice was greater than where it was plain1 and the ice carried away more load4 ,from areas where the surface was overspread by a great depth of loose material favorably disposed for removal1 more debris was taken than from areas where material in a condition to be readily transported was meager4 ,because of the topographic diversity and lithological heterogeneity of the surface of the country over which it passed1 some portions of the ice carried much more drift than others1 and when the ice finally melted1 greater depths of drift were left in some places than in others4 ,not all of the material transported by the ice was carried forward until the ice melted4 ,some of it was probably carried but a short distance from its original position before it lodged4 ,drift was thus accumulating at some points beneath the ice during its onward motion4 ,at such points the surface was being built up2 at other points1 abrasion was taking place1 and the surface was being cut down4 ,the drift mantle of any region does not1 therefore1 represent simply the material which was on and in and beneath the ice of that place at the time of its melting1 but it represents1 in addition1 all that lodged beneath the ice during its movement4 ,the constant tendency was for the ice to carry a considerable part of its load forward toward its thinned edge1 and there to leave it4 ,it follows that if the edge of the ice remained constant in position for any considerable period of time1 large quantities of drift would have accumulated under its marginal portion1 giving rise to a belt of relatively thick drift4 ,other things being equal1 the longer the time during which the position of the edge was stationary1 the greater the accumulation of drift4 ,certain ridge-like belts where the drift is thicker than on either hand1 are confidently believed to mark the position where the edge of the ice-sheet stood for considerable periods of time4 ,because of the unequal amounts of material carried by different parts of the ice1 and because of the unequal and inconstant conditions of deposition under the body of the ice and its edge1 the mantle of drift has a very variable thickness2 and a mantle of drift of variable thickness cannot fail to modify the topography of the region it covers4 ,the extent of the modification will depend on the extent of the variation4 ,this amounts in the aggregate1 to hundreds of feet4 ,the continental ice sheet1 therefore1 modified the topography of the region it covered1 not only by the wear it effected1 but also by the deposits it made4 ,in some places it chanced that the greater thicknesses of drift were left in the positions formerly marked by valleys4 ,locally the body of drift was so great that valleys were completely filled1 and therefore completely obliterated as surface features4 ,less frequently1 drift not only filled the valleys but rose even higher over their former positions than on either side4 ,in other places the greater depths of drift1 instead of being deposited in the valleys1 were left on pre-glacial elevations1 building them up to still greater heights4 ,in short1 the mantle of drift of unequal thickness was laid down upon the rock surface in such a manner that the thicker parts sometimes rest on hills and ridges1 sometimes on slopes1 sometimes on plains1 and sometimes in valleys4 ,illustration3 ,fig4 #cb4--;,diagrammatic section showing relation of drift to underlying rock1 where the drift is thick relative to the relief of the rock4 a and b represent the location of post-glacial valleys4 ,these relations are suggested by ,figs4 #cb and #cc4 ,from them it will be seen that in regions where the thickness of the drift is great1 relative to the relief of the underlying rock1 the topography may be completely changed4 ,not only may some of the valleys be obliterated by being filled1 but some of the hills may be obliterated by having the lower land between them built up to their level4 ,in regions where the thickness of the drift is slight1 relative to the relief of the rock beneath1 the hills cannot be buried1 and the valleys cannot be completely filled1 so that the relative positions of the principal topographic features will remain much the same after the deposition of the drift1 as before 7,fig4 #cc74 ,illustration3 ,fig4 #cc4--;,diagrammatic section showing relation of drift to underlying rock where the drift is thin relative to the relief of the underlying rock4 ,in case the pre-glacial valleys were filled and the hills buried1 the new valleys which the surface waters will in time cut in the drift surface will have but little correspondence in position with those which existed before the ice incursion4 ,a new system of valleys1 and therefore a new system of ridges and hills1 will be developed1 in some measure independent of the old4 ,these relations are illustrated by ,fig4 #cb4 ,inequalities in the thickness of drift lead to a still further modification of the surface4 ,it frequently happened that in a plane or nearly plane region a slight thickness of drift was deposited at one point1 while all about it much greater thicknesses were left4 ,the area of thin drift would then constitute a depression1 surrounded by a higher surface built up by the thicker deposits4 ,such depressions would at first have no outlets1 and are therefore unlike the depressions shaped by rain and river erosion4 ,the presence of depressions without outlets is one of the marks of a drift-covered 7glaciated7 country4 ,in these depressions water may collect1 forming lakes or ponds1 or in some cases only marshes and bogs4 ,,direction ,,of ,,ice ,,movement4 ,the direction in which glacier ice moved may be determined in various ways1 even after the ice has disappeared4 ,the shapes of the rock hills over which the ice passed1 the direction from which the materials of the drift came1 and the course of the margin of the drift1 all show that the ice of south central ,wisconsin was moving in a general southwest direction4 ,in the rock hills1 this is shown by the greater wear of their northeast 7stoss7 sides 7,plate ,,xxxiv74 ,from the course of the drift margin1 the general direction of movement may be inferred when it is remembered that the tendency of glacier ice on a plane surface is to move at right angles to its margin4 ,for the exact determination of the direction of ice movement1 recourse must be had to the striae on the bed-rock4 ,were the striated rock surface perfectly plane1 and were the striae even lines1 they would only tell that the ice was moving in one of two directions4 ,but the rock surface is not usually perfectly plane1 nor the striae even lines1 and between the two directions which lines alone might suggest1 it is usually possible to decide4 ,the minor prominences and depressions in the rock surface were shaped according to the same principles that govern the shaping of hills 7,fig4 #bi7 and valleys 7,fig4 #cj72 that is1 the stoss sides of the minor prominences1 and the distal sides of small depressions suffered the more wear4 ,with a good compass1 the direction of the striae may be measured to within a fraction of a degree1 and thus the direction of ice movement in a particular place be definitely determined4 ,the striae which have been determined about ,baraboo are shown on ,plate ,,ii4 ,effect of topography on movement4--,the effect of glaciation on topography has been sketched1 but the topography in turn exerted an important influence on the direction of ice movement4 ,the extreme degree of topographic influence is seen in mountain regions like the ,alps1 where most of the glaciers are confined strictly to the valleys4 ,as an ice sheet invades a region1 it advances first and farthest along the lines of least resistance4 ,in a rough country with great relief1 tongues or lobes of ice would push forward in the valleys1 while the hills or other prominences would tend to hold back or divide the onward moving mass4 ,the edge of an ice sheet in such a region would be irregular4 ,the marginal lobes of ice occupying the valleys would be separated by re-entrant angles marking the sites of hills and ridges4 ,if the ice crossed a plane surface above which rose a notable ridge or hill1 the first effect of the hill would be to indent the ice4 ,the ice would move forward on either side1 and if its thickness became sufficiently great1 the parts moving forward on either side would again unite beyond it4 ,a hill thus surrounded by ice is a nunatak4 ,later1 as the advancing mass of ice became thicker1 it might completely cover the hill2 but the thickness of ice passing over the hill would be less than that passing on either side by an amount equal to the height of the hill4 ,it follows that as ice encounters an isolated elevation1 three stages in its contest with the obstruction may be recognized3 7#a7 the stage when the ridge or hill acts as a wedge1 dividing the moving ice into lobes1 ,fig4 #cd2 7#b7 the nunatak stage1 when the ice has pushed forward and reunited beyond the hill1 ,fig4 #ce2 7#c7 the stage when the ice has become sufficiently deep to cover the hill4 ,illustration3 ,fig4 #cd4--;,diagrammatic representation of the effect of a hill on the edge of the ice4 ,after the ice has disappeared1 the influence of the obstruction might be found in the disposition of the drift4 ,if recession began during the first stage1 that is1 when the ice edge was separated into lobes1 the margin of the drift should be lobate1 and would loop back around the ridge from its advanced position on either side4 ,if recession began during the second stage1 that is1 when the lobes had become confluent and completely surrounded the hill1 a driftless area would appear in the midst of drift4 ,if recession began during the third stage1 that is1 after the ice had moved on over the obstruction1 the evidence of the sequence might be obliterated2 but if the ice moved but a short distance beyond the hill1 the thinner ice over the hill would have advanced less far than the thicker ice on either side 7,fig4 #ce71 and the margin of the drift would show a re-entrant pointing back toward the hill1 though not reaching it4 ,all these conditions are illustrated in the ,devil's lake region4 ,illustration3 ,fig4 #ce4--,same as ,fig4 #cd1 when the ice has advanced farther4 ,limit of the ,ice4 ,the region under description is partly covered with drift1 and partly free from it4 ,the limit of the ice1 at the time of its maximum expansion is well defined at many points1 and the nature and position of the drift limit are so unique as to merit attention 7see ,plates ,,ii and ,,xxxvii74 ,they illustrate many of the principles already discussed4 ,the ice which covered the region was the western margin of the ,green ,bay lobe 7,fig4 #cf7 of the last continental ice sheet4 ,its limit in this region is marked by a ridge-like accumulation of drift1 the terminal moraine1 which here has a general north-south direction4 ,the region may have been affected by the ice of more than one epoch1 but since the ice of the last epoch advanced as far to the west in this region as that of any earlier epoch1 the moraine is on the border between the glaciated country to the east1 and the driftless area to the west 7,plates ,i and ,,ii74 ,that part of the moraine which lies west of the ,wisconsin river follows a somewhat sinuous course from ,kilbourn ,city to a point a short distance north of ,prairie du ,sac4 ,the departures from this general course are especially significant of the behavior of glacier ice4 ,illustration3 ,fig4 #cf4--,map showing relations of lobes of ice during the ,wisconsin ice epoch1 to the driftless area4 ,in the great depression between the quartzite ranges1 the moraine bends westward1 showing that the ice advanced farther on the lowlands than on the ridges4 ,as the moraine of this low area approaches the south range1 it curves to the east4 ,at the point southwest of ,baraboo where the easterly curve begins to show itself1 the moraine lies at the north base of the quartzite range2 but as it is traced eastward1 it is found to lie higher and higher on the slope of the range1 until it reaches the crest nearly seven miles from the point where the eastward course was assumed4 ,at this point it crosses the range1 and1 once across the crest1 it turns promptly to the westward on the lower land to the south4 ,here the ice advanced up the valley between the ,east bluff 7east of the lake7 and the ,devil's nose 7,plate ,,xxxvii71 again illustrating the fact that lowlands favor ice advance4 ,the valley between the ,devil's nose and the ,east bluff is a narrow one1 and the ice advanced through it nearly to the present site of the lake4 ,meanwhile the restraining influence of the nose was making itself felt1 and the margin of the ice curved back from the bottom of the bluff near ,kirkland1 to the top of the bluff at the end of the nose4 ,here the edge of the ice crossed the point of the nose1 and after rounding it1 turned abruptly to the west4 ,thence its edge lay along the south slope of the ridge1 descending from the crest of the ridge at the nose1 to the base of the ridge two miles farther west4 ,here the ice reached its limit on the lowland1 and its edge1 as marked by the moraine1 turned southward1 reaching the ,wisconsin river about a mile and a half above ,prairie du ,sac4 ,the course of the terminal moraine across the ridges is such as the margin of the ice would normally have when it advanced into a region of great relief4 ,the great loop in the moraine with its eastern extremity at k1 ,plate ,,xxxvii1 is explained by the presence of the quartzite ridge which retarded the advancing ice while it moved forward on either side4 ,the minor loop around the ,devil's nose is explained in the same way4 ,both the main loop1 and the smaller one on the nose1 illustrate the point made earlier in the text4 ,the narrow and curious loop at m1 is of a slightly different origin1 though in principle the same4 ,it is in the lee of a high point in the quartzite ridge4 ,the ice surmounted this point1 and descended its western slope2 but the thickness of the ice passing over the summit was so slight that it advanced but a short distance down the slope before its force was exhausted1 while the thicker ice on either side advanced farther before it was melted4 ,glacial ,deposits4 ,before especial reference is made to the drift of this particular region1 it will be well to consider the character of drift deposits in general4 ,when the ice of the continental glacier began its motion1 it carried none of the stony and earthy debris which constitute the drift4 ,these materials were derived from the surface over which the ice moved4 ,from the method by which it was gathered1 it is evident that the drift of any locality may contain fragments of rock of every variety which occurs along the route followed by the ice which reached that locality4 ,where the ice had moved far1 and where there were frequent changes in the character of the rock constituting its bed1 the variety of materials in the drift is great4 ,the heterogeneity of the drift arising from the diverse nature of the rocks which contributed to it is lithological heterogeneity--a term which implies the commingling of materials derived from different rock formations4 ,thus it is common to find pieces of sandstone1 limestone1 quartzite1 granite1 gneiss1 schist1 etc41 intimately commingled in the drift1 wherever the ice which produced it passed over formations of these several sorts of rock4 ,lithological heterogeneity is one of the notable characteristics of glacial formations4 ,another characteristic of the drift is its physical heterogeneity4 ,as first gathered from the bed of moving ice1 some of the materials of the drift were fine and some coarse4 ,the tendency of the ice in all cases was to reduce its load to a still finer condition4 ,some of the softer materials1 such as soft shale1 were crushed or ground to powder1 forming what is known in common parlance as clay4 ,clayey 7fine7 material is likewise produced by the grinding action of ice-carried bowlders upon the rock-bed1 and upon one another4 ,other sorts of rock1 such as soft sandstone1 were reduced to the physical condition of sand1 instead of clay1 and from sand to bowlders all grades of coarseness and fineness are represented in the glacial drift4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,xxxv4 ,cut in drift1 showing its physical heterogeneity4 ,since the ice does not assort the material which it carries1 as water does1 the clay1 sand1 gravel and bowlders will not1 by the action of the ice1 be separated from one another4 ,they are therefore not stratified4 ,as left by the ice1 these physically heterogeneous materials are confusedly commingled4 ,the finer parts constitute a matrix in which the coarser are embedded4 ,physical heterogeneity 7,plate ,,xxxv71 therefore1 is another characteristic of glacial drift4 ,it is not to be understood that the proportions of these various physical elements1 clay1 sand1 gravel1 and bowlders1 are constant4 ,locally any one of them may predominate over any or all the others to any extent4 ,since lithological and physical heterogeneity are characteristics of glacial drift1 they together afford a criterion which is often of service in distinguishing glacial drift from other surface formations4 ,it follows that this double heterogeneity constitutes a feature which can be utilized in determining the former extension of existing glaciers1 as well as the former existence of glaciers where glaciers do not now exist4 ,another characteristic of glacial drift1 and one which clearly distinguishes it from all other formations with which it might be confounded1 is easily understood from its method of formation4 ,if the ice in its motion holds down rock debris upon the rock surface over which it passes with such pressure as to polish and striate the bed-rock1 the material carried will itself suffer wear comparable to that which it inflicts4 ,thus the stones1 large and small1 of glacial drift1 will be smoothed and striated4 ,this sort of wear on the transported blocks of rock1 is effected both by the bed-rock reacting on the bowlders transported over it1 and by bowlders acting on one another in and under the ice4 ,the wear of bowlders by bowlders is effected wherever adjacent ones are carried along at different rates4 ,since the rate of motion of the ice is different in different parts of the glacier1 the mutual abrasion of transported materials is a process constantly in operation4 ,a large proportion of the transported stone and blocks of rock may thus eventually become striated4 ,from the nature of the wear to which the stones are subjected when carried in the base of the ice1 it is easy to understand that their shapes must be different from those of water-worn materials4 ,the latter are rolled over and over1 and thus lose all their angles and assume a more or less rounded form4 ,the former1 held more or less firmly in the ice1 and pressed against the underlying rock or rock debris as they are carried slowly forward1 have their faces planed and striated4 ,the planation and striation of a stone need not be confined to its under surface4 ,on either side or above it other stones1 moving at different rates1 are made to abrade it1 so that its top and sides may be planed and scored4 ,if the ice-carried stones shift their positions1 as they may under various circumstances1 new faces will be worn4 ,the new face thus planed off may meet those developed at an earlier time at sharp angles1 altogether unlike anything which water-wear is capable of producing4 ,the stone thus acted upon shows a surface bounded by planes and more or less beveled1 instead of a rounded surface such as water wear produces4 ,we find1 then1 in the shape of the bowlders and smaller stones of the drift1 and in the markings upon their surfaces1 additional criteria for the identification of glacier drift 7,plate ,,xxxvi74 ,the characteristics of glacial drift1 so far as concerns its constitution1 may then be enumerated as1 7#a7 its lithological1 and 7#b7 physical heterogeneity2 7#c7 the shapes1 and 7#d7 the markings of the stones of the drift4 ,in structure1 the drift which is strictly glacial1 is unstratified4 ,in the broadest sense of the term1 all deposits made by glacier ice are moraines4 ,those made beneath the ice and back from its edge constitute the ground moraine1 and are distinguished from the considerable marginal accumulations which1 under certain conditions1 are accumulated at or near the margin4 ,these marginal accumulations are terminal moraines4 ,associated with the moraines which are the deposits of the ice directly1 there are considerable bodies of stratified gravel and sand1 the structure of which shows that they were laid down by water4 ,this is to be especially noted1 since lack of stratification is popularly supposed to be the especial mark of the formations to which the ice gave rise4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,xxxvi4 ,glaciated stones1 showing both form and striae4 7,matz47 ,these deposits of stratified drift lie partly beyond the terminal moraine1 and partly within it4 ,they often sustain very complicated relations both to the ground and terminal moraines4 ,the drift as a whole is therefore partly stratified and partly unstratified4 ,structurally the two types are thoroughly distinct1 but their relations are often most complex1 both horizontally and vertically4 ,a fuller consideration of these relations will be found on a later page4 ,the ,ground ,moraine4 ,the ground moraine constitutes the great body of the glacial drift4 ,bowlder clay1 a term descriptive of its constitution in some places1 and till1 are other terms often applied to the ground moraine4 ,the ground moraine consists of all the drift which lodged beneath the ice during its advance1 all that was deposited back from its edge while its margin was farthest south1 and most of that which was deposited while the ice was retreating4 ,from this mode of origin it is readily seen that the ground moraine should be essentially as widespread as the ice itself4 ,locally1 however1 it failed of deposition4 ,since it constitutes the larger part of the drift1 the characteristics already enumerated as belonging to drift in general are the characteristics of the till4 ,wherever obstacles to the progress of the ice lay in its path1 there was a chance that these obstacles1 rising somewhat into the lower part of the ice1 would constitute barriers against which debris in the lower part of the ice would lodge4 ,it might happen also that the ice1 under a given set of conditions favoring erosion1 would gather a greater load of rock-debris than could be transported under the changed conditions into which its advance brought it4 ,in this case1 some part of the load would be dropped and over-ridden4 ,especially near the margin of the ice where its thickness was slight and diminishing1 the ice must have found itself unable to carry forward the loads of debris which it had gathered farther back where its action was more vigorous4 ,it will be readily seen that if not earlier deposited1 all material gathered by the under surface of the ice would ultimately find itself at the edge of the glacier1 for given time enough1 ablation will waste all that part of the ice occupying the space between the original position of the debris1 and the margin of the ice4 ,under the thinned margin of the ice1 therefore1 considerable accumulations of drift must have been taking place while the ice was advancing4 ,while the edge of the ice sheet was advancing into territory before uninvaded1 the material accumulated beneath its edge at one time1 found itself much farther from the margin at another and later time4 ,under the more forcible ice action back from the margin1 the earlier accumulations1 made under the thin edge1 were partially or wholly removed by the thicker ice of a later time1 and carried down to or toward the new and more advanced margin4 ,here they were deposited1 to be in turn disturbed and transported still farther by the farther advance of the ice4 ,since in its final retreat the margin of the ice must have stood at all points once covered by it1 these submarginal accumulations of drift must have been made over the whole country once covered by the ice4 ,the deposits of drift made beneath the marginal part of the ice during its retreat1 would either cover the deposits made under the body of the ice at an earlier time1 or be left alongside them4 ,the constitution of the two phases of till1 that deposited during the advance of the ice1 and that deposited during its retreat1 is essentially the same1 and there is nothing in their relative positions to sharply differentiate them4 ,they are classed together as subglacial till4 ,subglacial till was under the pressure of the overlying ice4 ,in keeping with these conditions of accumulation1 the till often possesses a firmness suggestive of great compression4 ,where its constitution is clayey it is often remarkably tough4 ,where this is the case1 the quality here referred to has given rise to the suggestive name hard pan4 ,where the constitution of the till is sandy1 rather than clayey1 this firmness and toughness are less developed1 or may be altogether wanting1 since sand cannot be compressed into coherent masses like clay4 ,constitution4--,the till is composed of the more or less comminuted materials derived from the land across which the ice passed4 ,the soil and all the loose materials which covered the rock entered into its composition4 ,where the ice was thick and its action vigorous1 it not only carried away the loose material which it found in its path1 but1 armed with this material1 it abraded the underlying rock1 wearing down its surface and detaching large and small blocks of rock from it4 ,it follows that the constitution of the till at any point is dependent upon the nature of the soil and rock from which it was derived4 ,if sandstone be the formation which has contributed most largely to the till1 the matrix of the till will be sandy4 ,where limestone instead of sandstone made the leading contribution to it1 the till has a more earthy or clayey matrix4 ,any sort of rock which may be very generally reduced to a fine state of division under the mechanical action of the ice1 will give rise to clayey till4 ,the nature and the number of the bowlders in the till1 no less than the finer parts1 depend on the character of the rock overridden4 ,a hard and resistant rock1 such as quartzite1 will give rise to more bowlders in proportion to the total amount of material furnished to the ice1 than will softer rock4 ,shale or soft sandstone1 possessing relatively slight resistance1 will be much more completely crushed4 ,they will1 therefore1 yield proportionately fewer bowlders than harder formations1 and more of the finer constituents of till4 ,the bowlders taken up by the ice as it advanced over one sort of rock and another1 possessed different degrees of resistance4 ,the softer ones were worn to smaller dimensions or crushed with relative ease and speed4 ,bowlders of soft rock are1 therefore1 not commonly found in any abundance at great distances from their sources4 ,the harder ones yielded less readily to abrasion1 and were carried much farther before being destroyed1 though even such must have suffered constant reduction in size during their subglacial journey4 ,in general it is true that bowlders in the till1 near their parent formations1 are larger and less worn than those which have been transported great distances4 ,the ice which covered this region had come a great distance and had passed over rock formations of many kinds4 ,the till therefore contains elements derived from various formations2 that is1 it is lithologically heterogeneous4 ,this heterogeneity cannot fail to attract the attention of one examining any of the many exposures of drift about ,baraboo at road gradings1 or in the cuts along the railway4 ,among the stones in the drift at these exposures are limestone1 sandstone1 quartzite1 diabase1 gabbro1 gneiss1 granite1 schist1 and porphyry1 together with pieces of flint and chert4 ,such an array may be found at any of the exposures within the immediate vicinity of ,devil's lake4 ,to the north1 and a few miles to the south of the ,baraboo ranges1 the quartzite from these bluffs1 and the porphyry from the point marked h in ,plate ,,ii1 are wanting1 though other varieties of porphyry are present4 ,the ice moved in a general west-southwest direction in this region1 and the quartzite in the drift1 so far as derived from the local formation1 is therefore restricted to a narrow belt4 ,the physical heterogeneity may be seen at all exposures1 and is illustrated in ,plate ,,xxxv4 ,the larger stones of the drift are usually of some hard variety of rock4 ,near the ,baraboo ranges1 the local quartzite often predominates among the bowlders1 and since such bowlders have not been carried far1 they are often little worn4 ,away from the ranges1 the bowlders are generally of some crystalline rock1 such as granite and diabase4 ,bowlders of these sorts of rock are from a much more distant source1 and are usually well worn4 ,in general the till of any locality is made up largely of material derived from the formations close at hand4 ,this fact seems to afford sufficient warrant for the conclusion that a considerable amount of deposition must have gone on beneath the ice during its movement1 even back from its margin4 ,to take a concrete illustration1 it would seem that the drift of southeastern ,wisconsin should have had a larger contribution than it has of material derived from ,canadian territory1 if material once taken up by the ice was all or chiefly carried down to its thinned edge before deposition4 ,the fact that so little of the drift came from these distant sources would seem to prove that a large part of the material moved by the ice1 is moved a relatively short distance only4 ,the ice must be conceived of as continually depositing parts of its load1 and parts which it has carried but a short distance1 as it takes up new material from the territory newly invaded4 ,in keeping with the character of till in general1 that about ,devil's lake was derived largely from the sandstone1 limestone and quartzite of the immediate vicinity1 while a much smaller part of it came from more distant sources4 ,this is especially noticeable in the fine material1 which is made up mostly of the comminuted products of the local rock4 ,topography4--,the topography of the ground moraine is in general the topography already described in considering the modification of preglacial topography effected by ice deposition4 ,as left by the ice1 its surface was undulating4 ,the undulations did not take the form of hills and ridges with intervening valleys1 but of swells and depressions standing in no orderly relationship to one another4 ,undrained depressions are found in the ground moraine1 but they are1 as a rule1 broader and shallower than the kettles common to terminal moraines4 ,it is in the broad1 shallow depressions of the ground moraine that many of the lakes and more of the marshes of southeastern ,wisconsin are located4 ,the rolling1 undulating topography characteristic of ground moraines is well shown about the ,city of ,baraboo and between that point and the lake1 and at many less easily designated points about ,merrimac4 ,in thickness the ground moraine reaches at least #afj feet1 though its average is much less--too little to obliterate the greater topographic features of the rock beneath4 ,it is1 however1 responsible for many of the details of the surface4 ,terminal ,moraines4 ,the marginal portion of the ice sheet was more heavily loaded--certainly more heavily loaded relative to its thickness--than any other4 ,toward its margin the thinned ice was constantly losing its transportive power1 and at its edge this power was altogether gone4 ,since the ice was continually bringing drift down to this position and leaving it there1 the rate of drift accumulation must have been greater1 on the average1 beneath the edge of the ice than elsewhere4 ,whenever1 at any stage in its history1 the edge of the ice remained essentially constant in position for a long period of time1 the corresponding submarginal accumulation of drift was great1 and when the ice melted1 the former site of the stationary edge would be marked by a broad ridge or belt of drift1 thicker than that on either side4 ,such thickened belts of drift are terminal moraines4 ,it will be seen that a terminal moraine does not necessarily mark the terminus of the ice at the time of its greatest advance1 but rather its terminus at any time when its edge was stationary or nearly so4 ,from the conditions of their development it will be seen that these submarginal moraines may be made up of materials identical with those which constitute the ground moraine1 and such is often the case4 ,but water arising from the melting of the ice1 played a much more important role at its margin than farther back beneath it4 ,one result of its greater activity may be seen in the greater coarseness which generally characterizes the material of the terminal moraine as compared with that of the adjacent ground moraine4 ,this is partly because the water carried away such of the finer constituents as it was able to transport1 leaving the coarser behind4 ,further evidence of the great activity of water near the margin of the ice is to be seen in the relatively large amount of assorted and stratified sand and gravel associated with the terminal moraine4 ,such materials as were carried on the ice were dropped at its edge when the ice which bore them melted from beneath4 ,if the surface of the ice carried many bowlders1 many would be dropped along the line of its edge wherever it remained stationary for any considerable period of time4 ,a terminal moraine therefore embraces 7#a7 the thick belt of drift accumulated beneath the edge of the ice while it was stationary1 or nearly so2 and 7#b7 such debris as was carried on the surface of the ice and dumped at its margin4 ,in general the latter is relatively unimportant4 ,at various stages in its final retreat1 the ice made more or less protracted halts4 ,these halting places are marked by marginal moraines of greater or less size1 depending on the duration of the stop1 and the amount of load carried4 ,a terminal moraine is not the sharp and continuous ridge we are wont to think it4 ,it is a belt of thick drift1 rather than a ridge1 though it is often somewhat ridge-like4 ,in width1 it varies from a fraction of a mile to several miles4 ,in the region under consideration it is rarely more than fifty feet high1 and rarely less than a half mile wide1 and a ridge of this height and width is not a conspicuous topographic feature in a region where the relief is so great as that of the ,devil's lake region4 ,topography of terminal moraines4--,the most distinctive feature of a terminal moraine is not its ridge-like character1 but its peculiar topography4 ,in general1 it is marked by depressions without outlets1 associated with hillocks and short ridges comparable in dimensions to the depressions4 ,both elevations and depressions are1 as a rule1 more abrupt than in the ground moraine4 ,in the depressions there are many marshes1 bogs1 ponds and small lakes4 ,the shapes and the abundance of round and roundish hills have locally given rise to such names as ,the ,knobs1 ,short ,hills1 etc4 ,elsewhere the moraine has been named the ,kettle ,range from the number of kettle-like depressions in its surface4 ,it is to be kept in mind that it is the association of the knobs and kettles1 rather than either feature alone1 which is the distinctive mark of terminal moraine topography4 ,illustration3 ,fig4 #cg4--,sketch of terminal moraine topography1 on the quartzite ridge east of ,devil's lake4 7,matz47 ,the manner in which the topography of terminal moraines was developed is worthy of note4 ,in the first place1 the various parts of the ice margin carried unequal amounts of debris4 ,this alone would have caused the moraine of any region to have been of unequal height and width at different points4 ,in the second place1 the margin of the ice1 while maintaining the same general position during the making of a moraine1 was yet subject to many minor oscillations4 ,it doubtless receded to some slight extent because of increased melting during the summer1 to advance again during the winter4 ,in its recession1 the ice margin probably did not remain exactly parallel to its former position4 ,if some parts receded more than others1 the details of the line of its margin may have been much changed during a temporary retreat4 ,when the ice again advanced1 its margin may have again changed its form in some slight measure1 so as to be parallel neither with its former advanced position1 nor with its position after its temporary retreat4 ,with each successive oscillation of the edge1 the details of the margin may have altered1 and at each stage the marginal deposits corresponded with the edge4 ,there might even be considerable changes in the edge of the ice without any general recession or advance1 as existing glaciers show4 ,it was probably true of the margin of the ,american ice sheet1 as of existing glaciers1 that there were periods of years when the edge of the ice receded1 followed by like periods when it remained stationary or nearly so1 and these in turn followed by periods of advance4 ,during any advance1 the deposits made during the period of recession would be overridden and disturbed or destroyed4 ,if the ice were to retreat and advance repeatedly during a considerable period of time1 always within narrow limits1 and if during this oscillation the details of its margin were frequently changing1 the result would be a complex or tangle of minor morainic ridges of variable heights and widths4 ,between and among the minor ridges there would be depressions of various sizes and shapes4 ,thus1 it is conceived1 many of the peculiar hillocks and hollows which characterize terminal moraines may have arisen4 ,some of the depressions probably arose in another way4 ,when the edge of the ice retreated1 considerable detached masses of ice might be left beyond the main body4 ,this might be buried by gravel and sand washed out from the moraine4 ,on melting1 the former sites of such blocks of ice would be marked by kettles4 ,in the marginal accumulations of drift as first deposited1 considerable quantities of ice were doubtless left4 ,when this melted1 the drift settled and the unequal settling may have given rise to some of the topographic irregularities of the drift4 ,the terminal moraine about ,devil's lake4--,on the lower lands1 the terminal moraine of the ,devil's lake region has the features characteristic of terminal moraines in general4 ,it is a belt of thick drift varying in width from half a mile or less to three-quarters of a mile or more4 ,its surface is marked by numerous hills and short ridges1 with intervening depressions or kettles4 ,some of the depressions among the hills contain water1 making ponds or marshes1 though the rather loose texture of the drift of this region is not favorable to the retention of water4 ,the moraine belt1 as a whole1 is higher than the land on either side4 ,it is therefore somewhat ridge-like1 and the small1 short hills and ridges which mark its surface1 are but constituent parts of the larger1 broader ridge4 ,approached from the west1 that is from the driftless side1 the moraine on the lower lands is a somewhat prominent topographic feature1 often appearing as a ridge thirty1 forty or even fifty feet in height4 ,approached from the opposite direction1 that is1 from the ground moraine1 it is notably less prominent1 and its inner limit wherever located1 is more or less arbitrary4 ,illustration3 ,fig4 #ch4--;,cut through the terminal moraine just east of ,kirkland1 partially diagrammatic4 ,a deep1 fresh railway cut in the moraine southeast of ,devil's lake illustrates its complexity of structure1 a complexity which is probably no greater than that at many other points where exposures are not seen4 ,the section is represented in ,fig4 #ch4 ,the stratified sand to the right retains even the ripple-marks which were developed when it was deposited4 ,to the left1 at the same level1 there is a body of till 7unstratified drift71 over which is a bed of stoneless and apparently structureless clay4 ,in a depression just above the clay with till both to the right and left1 is a body of loam which possesses the characteristics of normal loess4 ,it also contains calcareous concretions1 though no shells have been found4 ,this occurrence of loess is the more noteworthy1 since loess is rarely found in association with drift of the last glacial epoch4#g #g ,an account of loess in connection with the drift of the last glacial epoch is given in the ,journal of ,geology1 ,vol4 ,,iv1 pp4 #ibi-ihg4 ,for a general account of loess1 see ,sixth ,annual ,report of ,u4,s4 ,geological ,survey4 ,the moraine on the main quartzite range4--,in tracing the moraine over the greater quartzite range1 it is found to possess a unique feature in the form of a narrow but sharply defined ridge of drift1 formed at the extreme margin of the ice at the time of its maximum advance4 ,for fully eleven miles1 with but one decided break1 and two short stretches where its development is not strong1 this unique marginal ridge separates the drift-covered country on the one hand1 from the driftless area on the other4 ,in its course the ridge lies now on slopes1 and now on summits1 but in both situations preserves its identity4 ,where it rests on a plain1 or nearly plain surface1 its width at base varies from six to fifteen rods1 and its average height is from twenty to thirty feet4 ,its crest is narrow1 often no more than a single rod4 ,where it lies on a slope1 it is asymmetrical in cross section 7see ,fig4 #ci71 the shorter slope having a vertical range of ten to thirty-five feet1 and its longer a range of forty to one hundred feet4 ,this asymmetrical form persists throughout all that portion of the ridge which lies on an inclined surface1 the slope of which does not correspond with the direction of the moraine4 ,where it lies on a flat surface1 or an inclined surface the slope of which corresponds in direction with the course of the ridge itself1 its cross section is more nearly symmetrical 7see ,fig4 #dj74 ,in all essential characteristics this marginal ridge corresponds with the ,end-,moraene of the ,germans4 ,illustration3 ,fig4 #ci4--;,diagrammatic cross-section of the marginal ridge as it occurs on the south slope of the ,devil's ,nose4 ,the slope below1 though glaciated1 is nearly free from drift4 ,illustration3 ,fig4 #dj4--;,diagrammatic cross-section of the marginal ridge as it appears when its base is not a sloping surface4 ,for the sake of bringing out some of its especially significant features1 the ridge may be traced in detail1 commencing on the south side of the west range4 ,where the moraine leaves the lowlands south of the ,devil's nose1 and begins the ascent of the prominence1 the marginal ridge first appears at about the #idj-;foot contour 7f1 ,plate ,,xxxvii74 ,though at first its development is not strong1 few rods have been passed before its crest is fifteen to twenty feet above the driftless area immediately to the north 7see ,fig4 #ci7 and from forty to one hundred feet above its base to the south1 down the slope4 ,in general the ridge becomes more distinct with increasing elevation1 and except for two or three narrow post-glacial erosion breaks1 is continuous to the very summit at the end of the nose 7g74 ,the ridge in fact constitutes the uppermost forty or forty-five feet of the crest of the nose1 which is the highest point of the west range within the area shown on the map4 ,throughout the whole of this course the marginal ridge lies on the south slope of the nose1 and has the asymmetrical cross section shown in ,fig4 #ci4 ,above 7north of7 the ridge at most points not a bowlder of drift occurs4 ,so sharply is its outer 7north7 margin defined1 that at many points it is possible to locate it within the space of less than a yard4 ,at the crest of the nose 7g7 the marginal ridge1 without a break1 swings northward1 and in less than a quarter of a mile turns again to the west4 ,bearing to the north it presently reaches 7at h7 the edge of the precipitous bluff1 bordering the great valley at the south end of the lake4 ,between the two arms of the loop thus formed1 the surface of the nose is so nearly level that it could have offered no notable opposition to the progress of the ice1 and yet it failed to be covered by it4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,xxxvii4 ,topographic map 7contour interval #ajj feet7 of a small area about ,devil's lake1 taken from the ,baraboo sheet of the ,united ,states ,geological ,survey4 ,each contour line connects points of the same elevation1 and the figures upon them give the heights above sea level4 ,where contour lines lie close together1 they indicate steep slopes4 ,in the great valley between the nose and the east bluff1 the marginal ridge does not appear4 ,in the bottom of the valley the moraine takes on its normal form1 and the slopes of the quartzite ridges on either hand are much too steep to allow any body of drift1 or loose material of any sort1 to lodge on them4 ,ascending the east bluff a little east of the point where the drift ridge drops off the west bluff1 the ridge is again found 7at i7 in characteristic development4 ,for some distance it is located at the edge of the precipitous south face of the bluff4 ,farther on it bears to the north1 and soon crosses a col 7j7 in the ridge1 building it up many feet above the level of the bed-rock4 ,from this point eastward for about three miles the marginal ridge is clearly defined1 the slopes about equal on either side1 and the crest as nearly even as the topography of the underlying surface permits4 ,the topographic relations in this part of the course are shown in ,fig4 #dj4 ,at k1 this marginal ridge attains its maximum elevation1 #a1fbj feet4 ,at this great elevation1 the ridge turns sharply to the northwest at an angle of more than #ij deg44 ,following this direction for little more than half a mile1 it turns to the west4 ,at some points in this vicinity the ridge assumes the normal morainic habit1 but this is true for short distances only4 ,farther west1 at l1 it turns abruptly to the northeast and is sharply defined4 ,it here loops about a narrow area less than sixty rods wide1 and over half a mile in length1 the sharpest loop in its whole course4 ,the driftless tract enclosed by the arms of this loop is lower than the drift ridge on either hand4 ,the ice on either side would need to have advanced no more than thirty rods to have covered the whole of it4 ,from the minor loop just mentioned1 the marginal ridge is continued westward1 being well developed for about a mile and a half4 ,at this point the moraine swings south to the north end of ,devil's lake1 loses the unique marginal ridge which has characterized its outer edge across the quartzite range for so many miles1 and assumes the topography normal to terminal moraines4 ,at no other point in the ,united ,states1 so far as known to the writers1 is there so sharply marked a marginal ridge associated with the terminal moraine1 for so long a distance4 ,from ,plate ,,ii it will be seen that the moraine as a whole makes a great loop to the eastward in crossing the quartzite range4 ,from the detailed description just given of the course of the marginal ridge1 it will be seen that it has three distinct loops2 one on the ,devil's nose 7west of g1 ,plate ,,xxxvii72 one on the main ridge 7west of k7 and a minor one on the north side of the last 7southwest of m74 ,the first and third are but minor irregularities on the sides of the great loop1 the head of which is at k4 ,the significant fact in connection with these irregularities in the margin of the moraine is that each loop stands in a definite relation to a prominence4 ,the meaning of this relation is at once patent4 ,the great quartzite range was a barrier to the advance of the ice4 ,acting as a wedge1 it caused a re-entrant in the advancing margin of the glacier4 ,the extent and position of the re-entrant is shown by the course of the moraine in ,plate ,,ii4 ,thus the great loop in the moraine1 the head of which is at k1 ,plate ,,xxxvii1 was caused by the quartzite range itself4 ,the minor loops on the sides of the major are to be explained on the same principle4 ,northeast of the minor loop on the north side of the larger one 7m7 there are two considerable hills1 reaching an elevation of nearly #a1ejj feet4 ,though the ice advancing from the east-northeast overrode them1 they must have acted like a wedge1 to divide it into lobes4 ,the ice which reached their summits had spent its energy in so doing1 and was unable to move forward down the slope ahead1 and the thicker bodies of ice which passed on either side of them1 failed to unite in their lee 7compare ,figs4 #cd and #ce74 ,the application of the same principle to the loop on the ,devil's nose is evident4 ,constitution of the marginal ridge4--,the material in the marginal ridge1 as seen where erosion has exposed it1 is till1 abnormal1 if at all1 only in the large percentage of widely transported bowlders which it contains4 ,this is especially true of the surface1 where in some places #ij per cent4 of the large bowlders are of very distant origin1 and that in spite of the fact that the ice which deposited them had just risen up over a steep slope of quartzite1 which could easily have yielded abundant bowlders4 ,in other places the proportion of foreign bowlders is small1 no more than one in ten4 ,in general1 however1 bowlders of distant origin predominate over those derived close at hand4 ,the slope of the upper surface of the ice at the margin4--,the marginal ridge on the south slope of ,devil's nose leads to an inference of especial interest4 ,its course lies along the south slope of the nose1 from its summit on the east to its base on the west4 ,throughout this course the ridge marks with exactness the position of the edge of the ice at the time of its maximum advance1 and its crest must therefore represent the slope of the upper surface of the ice at its margin4 ,the western end of the ridge 7f1 ,plate ,,xxxvii7 has an altitude of #idj feet1 and its eastern end 7g7 is just above the #a1ejj-;foot contour4 ,the distance from the one point to the other is one and three-fourths miles1 and the difference in elevation1 #efj feet4 ,these figures show that the slope of the ice along the south face of this bluff was about #cbj feet per mile4 ,this1 so far as known1 is the first determination of the slope of the edge of the continental ice sheet at its extreme margin4 ,it is to be especially noted that these figures are for the extreme edge of the ice only4 ,the angle of slope back from the edge was doubtless much less4 ,stratified ,drift4 ,while it is true that glacier ice does not distinctly stratify the deposits which it makes1 it is still true that a very large part of the drift for which the ice of the glacial period was directly or indirectly responsible is stratified4 ,that this should be so is not strange when it is remembered that most of the ice was ultimately converted into running water1 just as the glaciers of today are4 ,the relatively small portion which disappeared by evaporation was probably more than counterbalanced1 at least near the margin of the ice1 by the rain which fell upon it4 ,it cannot be considered an exaggeration1 therefore1 to say that the total amount of water which operated on the drift1 first and last1 was hardly less than the total amount of the ice itself4 ,the drift deposited by the marginal part of the ice was affected during its deposition1 not only by the water which arose from the melting of the ice which did the depositing1 but by much water which arose from the melting of the ice far back from the margin4 ,the general mobility of the water1 as contrasted with ice1 allowed it to concentrate its activities along those lines which favored its motion1 so that different portions of the drift were not affected equally by the water of the melting ice4 ,all in all it will be seen that the water must have been a very important factor in the deposition of the drift1 especially near the margin of the ice4 ,but the ice sheet had a marginal belt throughout its whole history1 and water must have been active and effective along this belt1 not only during the decadence of the ice sheet1 but during its growth as well4 ,it is further to be noted that any region of drift stood good chance of being operated upon by the water after the ice had departed from it1 so that in regions over which topography directed drainage after the withdrawal of the ice1 the water had the last chance at the drift1 and modified it in such a way and to such an extent as circumstances permitted4 ,its origin4--,there are various ways in which stratified drift may arise in connection with glacier deposits4 ,it may come into existence by the operation of water alone2 or by the co-operation of ice and water4 ,where water alone was immediately responsible for the deposition of stratified drift1 the water concerned may have owed its origin to the melting ice1 or it may have existed independently of the ice in the form of lakes4 ,when the source of the water was the melting ice1 the water may have been running1 when it was actively concerned in the deposition of stratified drift2 or it may have been standing 7glacial lakes and ponds71 when it was passively concerned4 ,when ice co-operated with water in the development of stratified drift the ice was generally a passive partner4 ,glacial drainage4--,the body of an ice sheet during any glacial period is probably melting more or less at some horizons all the time1 and at all horizons some of the time4 ,most of the water which is produced at the surface during the summer sinks beneath it4 ,some of it may congeal before it sinks far1 but much of it reaches the bottom of the ice without refreezing4 ,it is probable that melting is much more nearly continuous in the body of a moving ice sheet than at its surface1 and that some of the water thus produced sinks to the bottom of the ice without refreezing4 ,at the base of the ice1 so long as it is in movement1 there is doubtless more or less melting1 due both to friction and to the heat received by conduction from the earth below4 ,thus in the ice and under the ice there must have been more or less water in motion throughout essentially all the history of an ice sheet4 ,if it be safe to base conclusions on the phenomena of existing glaciers1 it may be assumed that the waters beneath the ice1 and to a less extent the waters in the ice1 organized themselves to a greater or less degree into streams4 ,for longer or shorter distances these streams flowed in the ice or beneath it4 ,ultimately they escaped from its edge4 ,the subglacial streams doubtless flowed1 in part1 in the valleys which affected the land surface beneath the ice1 but they were probably not all in such positions4 ,the courses of well-defined subglacial streams were tunnels4 ,the bases of the tunnels were of rock or drift1 while the sides and tops were of ice4 ,it will be seen1 therefore1 that their courses need not have corresponded with the courses of the valleys beneath the ice4 ,they may sometimes have followed lines more or less independent of topography1 much as water may be forced over elevations in closed tubes4 ,it is not to be inferred1 however1 that the subglacial streams were altogether independent of the sub-ice topography4 ,the tunnels in which the water ran probably had too many leaks to allow the water to be forced up over great elevations4 ,this1 at least1 must have been the case where the ice was thin or affected by crevasses4 ,under such circumstances the topography of the land surface must have been the controlling element in determining the course of the subglacial drainage4 ,when the streams issued from beneath the ice the conditions of flow were more or less radically changed1 and from their point of issue they followed the usual laws governing river flow4 ,if the streams entered static water as they issued from the ice1 and this was true where the ice edge reached the sea or a lake1 the static water modified the results which the flowing waters would otherwise have produced4 ,stages in the history of an ice sheet4--,the history of an ice sheet which no longer exists involves at least two distinct stages4 ,these are 7#a7 the period of growth1 and 7#b7 the period of decadence4 ,if the latter does not begin as soon as the former is complete1 an intervening stage1 representing the period of maximum ice extension1 must be recognized4 ,in the case of the ice sheets of the glacial period1 each of these stages was probably more or less complex4 ,the general period of growth of each ice sheet is believed to have been marked by temporary1 but by more or less extensive intervals of decadence1 while during the general period of decadence1 it is probable that the ice was subject to temporary1 but to more or less extensive intervals of recrudescence4 ,for the sake of simplicity1 the effects of these oscillations of the edge of the ice will be neglected at the outset1 and the work of the water accompanying the two or three principal stages of an ice sheet's history will be outlined as if interruptions in the advance and in the retreat1 respectively1 had not occurred4 ,as they now exist1 the deposits of stratified drift made at the edge of the ice or beyond it during the period of its maximum extension present the simplest1 and at the same time most sharply defined phenomena1 and are therefore considered first4 ,deposits ,made by ,extraglacial ,waters ,during the ,maximum ,extension of the ,ice4 ,the deposits made by the water at the time of the maximum extension of the ice and during its final retreat1 were never disturbed by subsequent glacier action4 ,so far as not destroyed by subsequent erosion1 they still retain the form and structure which they had at the outset4 ,such drift deposits1 because they lie at the surface1 and because they are more or less distinct topographically as well as structurally1 are better known than the stratified drift of other stages of an ice sheet's history4 ,of stratified drift made during the maximum extension of the ice1 and during its final retreat1 there are several types4 ,a4 ,at the edge of ice1 on land4--,if the subglacial streams flowed under head1 the pressure was relieved when they escaped from the ice4 ,with this relief1 there was diminution of velocity4 ,with the diminution of velocity1 deposition of load would be likely to take place4 ,since these changes would be likely to occur at the immediate edge of the ice1 one class of stratified drift deposits would be made in this position1 in immediate contact with the edge of the ice1 and their form would be influenced by it4 ,at the stationary margin of an ice sheet1 therefore1 at the time of its maximum advance1 ice and water must have co-operated to bring into existence considerable quantities of stratified drift4 ,the edge of the ice was probably ragged1 as the ends of glaciers are today1 and as the waters issued from beneath it1 they must frequently have left considerable quantities of such debris as they were carrying1 against its irregular margin1 and in its re-entrant angles and marginal crevasses4 ,when the ice against which this debris was first lodged melted1 the marginal accumulations of gravel and sand often assumed the form of kames4 ,a typical kame is a hill1 hillock1 or less commonly a short ridge of stratified drift2 but several or many are often associated1 giving rise to groups and areas of kames4 ,kames are often associated with terminal moraines1 a relation which emphasizes the fact of their marginal origin4 ,so far as the superficial streams which flowed to the edge of the ice carried debris1 this was subject to deposition as the streams descended from the ice4 ,such drift would tend to increase the body of marginal stratified drift from subglacial sources4 ,marginal accumulations of stratified drift1 made by the co-operation of running water and ice1 must have had their most extensive development1 other things being equal1 where the margin of the ice was longest in one position1 and where the streams were heavily loaded4 ,the deposits made by water at the edge of the ice differ from those of the next class--made beyond the edge of the ice--in that they were influenced in their disposition and present topography1 by the presence of ice4 ,in the ,devil's lake region isolated and well-defined kames are not of common occurrence4 ,there are1 however1 at many points hills which have something of a kame-like character4 ,there is such a hill a mile southeast of the ,court house at ,baraboo1 at the point marked p1 ,plate ,,xxxvii4 ,in this hill there are good exposures which show its structure4 ,there are many hillocks of a general kame-like habit associated with the terminal moraine south of the main quartzite range1 and north of the ,wisconsin river4 ,many of them occur somewhat within the terminal moraine a few miles northwest of ,merrimac4 ,b4 ,beyond the edge of the ice1 on land4--,as the waters escaping from the ice flowed farther1 deposits of stratified drift were made quite beyond the edge of the ice4 ,the forms assumed by such deposits are various1 and depended on various conditions4 ,where the waters issuing from the edge of the ice found themselves concentrated in valleys1 and where they possessed sufficient load1 and not too great velocity1 they aggraded the valleys through which they flowed1 developing fluvial plains of gravel and sand1 which often extended far beyond the ice4 ,such fluvial plains of gravel and sand constitute the valley trains which extend beyond the unstratified glacial drift in many of the valleys of the ,united ,states4 ,they are found especially in the valleys leading out from the stouter terminal moraines of late glacial age4 ,from these moraines1 the more extensive valley trains take their origin1 thus emphasizing the fact that they are deposits made by water beyond a stationary ice margin4 ,valley trains have all the characteristics of alluvial plains built by rapid waters carrying heavy loads of detritus4 ,now and then their surfaces present slight variations from planeness1 but they are minor4 ,like all plains of similar origin they decline gradually1 and with diminishing gradient1 down stream4 ,they are of coarser material near their sources1 and of finer material farther away4 ,valley trains constitute a distinct topographic as well as genetic type4 ,a perfect example of a valley train does not occur within the region here discussed4 ,there is such a train starting at the moraine where it crosses the ,wisconsin river above ,prairie du ,sac1 and extending down that valley to the ,mississippi1 but at its head this valley train is wide and has the appearance of an overwash plain1 rather than a valley train4 ,farther from the moraine1 however1 it narrows1 and assumes the normal characteristics of a valley train4 ,it is the gravel and sand of this formation which underlies ,sauk ,prairie1 and its topographic continuation to the westward4 ,where the subglacial streams did not follow subglacial valleys1 they did not always find valleys when they issued from the ice4 ,under such circumstances1 each heavily loaded stream coming out from beneath the ice must have tended to develop a plain of stratified material near its point of issue--a sort of alluvial fan4 ,where several such streams came out from beneath the ice near one another1 their several plains1 or fans1 were likely to become continuous by lateral growth4 ,such border plains of stratified drift differ from valley trains particularly 7#a7 in being much less elongate in the direction of drainage2 7#b7 in being much more extended parallel to the margin of the ice2 and 7#c7 in not being confined to valleys4 ,such plains stood an especially good chance of development where the edge of the ice remained constant for a considerable period of time1 for it was under such conditions that the issuing waters had opportunity to do much work4 ,thus arose the type of stratified drift variously known as overwash plains1 outwash plains1 morainic plains1 and morainic aprons4 ,these plains sometimes skirt the moraine for many miles at a stretch4 ,overwash plains may sometimes depart from planeness by taking on some measure of undulation1 of the sag and swell 7kame7 type1 especially near their moraine edges4 ,the same is often true of the heads of valley trains4 ,the heads of valley trains and the inner edges of overwash plains1 it is to be noted1 occupy the general position in which kames are likely to be formed1 and the undulations which often affect these parts of the trains and plains1 respectively1 are probably to be attributed to the influence of the ice itself4 ,valley trains and overwash plains1 therefore1 at their upper ends and edges respectively1 may take on some of the features of kames4 ,indeed1 either may head in a kame area4 ,good examples of overwash or outwash plains may be seen at various points in the vicinity of ,baraboo4 ,the plain west of the moraine just south of the main quartzite ridge has been referred to under valley trains4 ,in ,sauk ,prairie1 however1 its characteristics are those of an outwash plain1 rather than those of a valley train4 ,illustration3 ,fig4 #da4--,the morainic or outwash plain bordering the terminal moraine4 ,the figure is diagrammatic1 but represents1 in cross section1 the normal relation as seen south of the quartzite range at the east edge of ,sauk ,prairie1 north of the ,baraboo river and at some points between the ,south range and the ,baraboo4 ,a good example of an outwash plain occurs southwest of ,baraboo1 flanking the moraine on the west 7,fig4 #da74 ,seen from the west1 the moraine just north of the south quartzite range stands up as a conspicuous ridge twenty to forty feet above the morainic plain which abuts against it4 ,traced northward1 the edge of the outwash plain1 as it abuts against the moraine1 becomes higher1 and in ,section #d1 ,township #aa ,n41 ,range #f ,e41 the moraine edge of the plain reaches the crest of the moraine 7,fig4 #db74 ,from this point north to the ,baraboo river the moraine scarcely rises above the edge of the outwash beyond4 ,illustration3 ,fig4 #db4--,the outwash plain is built up to the crest of the moraine4 ,the figure is diagrammatic1 but this relation is seen at the point marked ,w1 ,plate ,,ii4 ,north of the ,baraboo river the moraine is again distinct and the overwash plain to the west well developed much of the way from the ,baraboo to ,kilbourn ,city4 ,a portion of it is known as ,webster's ,prairie4 ,locally1 the outwash plains of this region have been much dissected by erosion since their deposition1 and are now affected by many small valleys4 ,in composition these plains are nearly everywhere gravel and sand1 the coarser material being nearer the moraine4 ,the loose material is in places covered by a layer of loam several feet deep1 which greatly improves the character of the soil4 ,this is especially true of ,sauk ,prairie1 one of the richest agricultural tracts in the state4 ,when the waters issuing from the edge of the ice were sluggish1 whether they were in valleys or not1 the materials which they carried and deposited were fine instead of coarse1 giving rise to deposits of silt1 or clay1 instead of sand or gravel4 ,at many points near the edge of the ice during its maximum stage of advance1 there probably issued small quantities of water not in the form of well-defined streams1 bearing small quantities of detritus4 ,these small quantities of water1 with their correspondingly small loads1 were unable to develop considerable plains of stratified drift1 but produced small patches instead4 ,such patches have received no special designation4 ,in the deposition of stratified drift beyond the edge of the ice1 the latter was concerned only in so far as its activity helped to supply the water with the necessary materials4 ,c4 ,deposits at and beyond the edge of the ice in standing water4--,the waters which issued from the edge of the ice sometimes met a different fate4 ,the ice in its advance often moved up river valleys4 ,when at the time of its maximum extension1 it filled the lower part of a valley1 leaving the upper part free1 drainage through the valley stood good chance of being blocked4 ,where this happened a marginal valley lake was formed4 ,such a lake was formed in the valley of the ,baraboo when the edge of the ice lay where the moraine now is 7,plate ,,ii74 ,the waters which were held back by the ice dam1 reinforced by the drainage from the ice itself1 soon developed a lake above the point of obstruction4 ,this extinct lake may be named ,baraboo lake4 ,in this lake deposits of laminated clay were made4 ,they are now exposed in the brick yards west of ,baraboo1 and in occasional gullies and road cuts in the flat bordering the river4 ,at the point marked s 7,plate ,,xxxvii7 there was1 in glacial times1 a small lake having an origin somewhat different from that of ,baraboo lake4 ,the former site of the lake is now marked by a notable flat4 ,excavations in the flat show that it is made up of stratified clay1 silt1 sand and gravel1 to the depth of many feet1--locally more than sixty4 ,these lacustrine deposits are well exposed in the road cuts near the northwest corner of the flat1 and in washes at some other points4 ,plate ,,xxxviii shows some of the silt and clay1 the laminae of which are much distorted4 ,deltas must have been formed where well-defined streams entered the lakes1 and subaqueous overwash plains where deltas became continuous by lateral growth4 ,the accumulation of stratified drift along the ice-ward shores of such lakes must have been rapid1 because of the abundant supply of detritus4 ,these materials were probably shifted about more or less by waves and shore currents1 and some of them may have been widely distributed4 ,out from the borders of such lakes1 fine silts and clays must have been in process of deposition1 at the same time that the coarse materials were being laid down nearer shore4 ,illustration3 ,,wisconsin ,,geol4 ,,and ,,nat4 ,,hist4 ,,survey4 ,,bulletin ,,no4 ,v41 ,,pl4 ,,xxxviii4 ,distorted laminae of silt and clay4 ,good examples of deltas and subaqueous overwash plains do not appear to exist in the region1 although conditions for their development seem to have been present4 ,thus in the lake which occupied the valley of the ,baraboo1 conditions would seem to have been ideal for the development of such features2 that is1 the overwash plains previously described should1 theoretically1 have been subaqueous overwash plains2 but if this be their character1 their distinctive marks have been destroyed by subsequent erosion4 ,during the maximum extension of an ice sheet1 therefore1 there was chance for the development1 at its edge or beyond it1 of the following types of stratified drift3 7#a7 kames and kame belts1 at the edge of the ice2 7#b7 fluvial plains or valley trains1 in virtual contact with the ice at their heads2 7#c7 border plains or overwash plains1 in virtual contact with the ice at their upper edges2 7#d7 ill-defined patches of stratified drift1 coarse or fine near the ice2 7#e7 subaqueous overwash plains and deltas1 formed either in the sea or lakes at or near the edge of the ice2 7#f7 lacustrine and marine deposits of other sorts1 the materials for which were furnished by the waters arising from the ice4 ,so far as this region is concerned1 all the deposits made in standing water were made in lakes4 ,deposits ,made by ,extraglacial ,waters ,during the ,retreat of the ,ice4 ,during the retreat of any ice sheet1 disregarding oscillations of its edge1 its margin withdrew step by step from the position of extreme advance to its center4 ,when the process of dissolution was complete1 each portion of the territory once covered by the ice1 had at some stage in the dissolution1 found itself in a marginal position4 ,at all stages in its retreat the waters issuing from the edge of the ice were working in the manner already outlined in the preceding paragraphs4 ,two points of difference only need be especially noted4 ,in the first place the deposits made by waters issuing from the retreating ice were laid down on territory which the ice had occupied1 and their subjacent stratum was often glacial drift4 ,so far as this was the case1 the stratified drift was super-morainic1 not extra-morainic4 ,in the second place the edge of the ice in retreat did not give rise to such sharply marked formations as the edge of the ice which was stationary4 ,the processes which had given rise to valley trains1 overwash plains1 kames1 etc41 while the ice edge was stationary1 were still in operation1 but the line or zone of their activity 7the edge of the ice7 was continually retreating1 so that the foregoing types1 more or less dependent on a stationary edge1 were rarely well developed4 ,as the ice withdrew1 therefore1 it allowed to be spread over the surface it had earlier occupied1 many incipient valley trains1 overwash plains1 and kames1 and a multitude of ill-defined patches of stratified drift1 thick and thin1 coarse and fine4 ,wherever the ice halted in its retreat1 these various types stood chance of better development4 ,such deposits did not cover all the surface discovered by the ice in its retreat1 since the issuing waters1 thanks to their great mobility1 concentrated their activities along those lines which favored their motion4 ,nevertheless the aggregate area of the deposits made by water outside the ice as it retreated1 was great4 ,it is to be noted that it was not streams alone which were operative as the ice retreated4 ,as its edge withdrew1 lakes and ponds were continually being drained1 as their outlets1 hitherto choked by the ice1 were opened1 while others were coming into existence as the depressions in the surface just freed from ice1 filled with water4 ,lacustrine deposits at the edge of the ice during its retreat were in all essential respects identical with those made in similar situations during its maximum extension4 ,disregarding oscillations of the ice edge at these stages1 the deposits made by extraglacial waters during the maximum extension of an ice sheet1 and during its retreat1 were always left at the surface1 so far as the work of that ice sheet was concerned4 ,the stratified drift laid down by extraglacial waters in these stages of the last ice sheet which affected any region of our continent still remain at the surface in much the condition in which they were deposited1 except for the erosion they have since suffered4 ,it is because of their position at the surface that the deposits referable to these stages of the last ice sheet of any given region have received most attention and are therefore most familiar4 ,deposits ,made by ,extraglacial ,waters ,during the ,advance of the ,ice4 ,during the advance of an ice sheet1 if its edge forged steadily forward1 the waters issuing from it1 and flowing beyond1 were effecting similar results4 ,they were starting valley trains1 overwash plains1 kames1 and small ill-defined patches of stratified drift which the ice did not allow them to complete before pushing over them1 thus moving forward the zone of activity of extraglacial waters4 ,unlike the deposits made by the waters of the retreating ice1 those made by the waters of the advancing stage were laid down on territory which had not been glaciated1 or at least not by the ice sheet concerned in their deposition4 ,if the ice halted in its advance1 there was at such time and place opportunity for the better development of extraglacial stratified drift4 ,lakes as well as streams were concerned in the making of stratified beds of drift1 during the advance of the ice4 ,marginal lakes were obliterated by having their basins filled with the advancing ice1 which displaced the water4 ,but new ones were formed1 on the whole1 as rapidly as their predecessors became extinct1 so that lacustrine deposits were making at intervals along the margin of the advancing ice4 ,deposits made in advance of a growing ice sheet1 by waters issuing from it1 were subsequently overridden by the ice1 to the limit of its advance1 and in the process1 suffered destruction1 modification1 or burial1 in whole or in part1 so that now they rarely appear at the surface4 ,deposits ,made by ,subglacial ,streams4 ,before their issuance from beneath the ice1 subglacial waters were not idle4 ,their activity was sometimes erosive1 and at such times stratified deposits were not made4 ,but where the sub-glacial streams found themselves overloaded1 as seems frequently to have been the case1 they made deposits along their lines of flow4 ,where such waters were not confined to definite channels1 their deposits probably took on the form of irregular patches of silt1 sand1 or gravel2 but where depositing streams were confined to definite channels1 their deposits were correspondingly concentrated4 ,when subglacial streams were confined to definite channels1 the same may have been constant in position1 or may have shifted more or less from side to side4 ,where the latter happened there was a tendency to the development of a belt or strip of stratified drift having a width equal to the extent of the lateral migrations of the under-ice stream4 ,where the channel of the subglacial stream remained fixed in position1 the deposition was more concentrated1 and the bed was built up4 ,if the stream held its course for a long period of time1 the measure of building may have been considerable4 ,in so far as these channel deposits were made near the edge of the ice1 during the time of its maximum extension or retreat1 they were likely to remain undisturbed during its melting4 ,the aggraded channels then came to stand out as ridges4 ,these ridges of gravel and sand are known as osars or eskers4 ,it is not to be inferred that eskers never originated in other ways1 but it seems clear that this is one method1 and probably the principal one1 by which they came into existence4 ,eskers early attracted attention1 partly because they are relatively rare1 and partly because they are often rather striking topographic features4 ,the essential conditions1 therefore1 for their formations1 so far as they are the product of subglacial drainage1 are 7#a7 the confining of the subglacial streams to definite channels2 and 7#b7 a sufficient supply of detritus4 ,one esker only has been found in the region under consideration4 ,it is located at the point marked j1 ,plate ,,ii1 seven and one-half miles northeast of ,merrimac and one and one-half miles south of ,alloa 7g1 ,plate ,,ii74 ,the esker is fully a quarter of a mile long1 about thirty feet high1 and four rods wide at its base4 ,subglacial deposits of stratified drift were sometimes made on unstratified drift 7till7 already deposited by the ice before the location of the stream1 and sometimes on the rock surfaces on which no covering of glacier drift had been spread4 ,it is to be kept in mind that subglacial drainage was operative during the advance of an ice sheet1 during its maximum extension1 and during its retreat1 and that during all these stages it was effecting its appropriate results4 ,it will be readily seen1 however1 that all deposits made by subglacial waters1 were subject to modification or destruction or burial1 through the agency of the ice1 and that those made during the advance of the ice were less likely to escape than those made during its maximum extension or retreat4 ,,relations ,,of ,,stratified ,,to ,,unstratified ,,drift4 ,when it is remembered that extraglacial and subglacial waters were active at all stages of an ice sheet's history1 giving rise1 or tending to give rise to all the phases of stratified drift enumerated above2 when it is remembered that the ice of several epochs affected much of the drift-covered country2 and when it is remembered further that the edge of the ice both during advance and retreat was subject to oscillation1 and that each advance was likely to bury the stratified drift last deposited1 beneath unstratified1 it will be seen that the stratified drift and the unstratified had abundant opportunity to be associated in all relationships and in all degrees of intimacy1 and that the relations of the one class of drift to the other may come to be very complex4 ,as a result of edge oscillation1 it is evident that stratified drift may alternate with unstratified many times in a formation of drift deposited during a single ice epoch1 and that two beds of till1 separated by a bed of stratified drift1 do not necessarily represent two distinct glacial epochs4 ,the extent of individual beds of stratified drift1 either beneath the till or inter-bedded with it1 may not be great1 though their aggregate area and their aggregate volume is very considerable4 ,it is to be borne in mind that the ice1 in many places1 doubtless destroyed all the stratified drift deposited in advance on the territory which it occupied later1 and that in others it may have left only patches of once extensive sheets4 ,this may help to explain why it so frequently happens that a section of drift at one point shows many layers of stratified drift1 while another section close by1 of equal depth1 and in similar relationships1 shows no stratified material whatsoever4 ,such deposits as were made by superglacial streams during the advance of the ice must likewise have been delivered on the land surface1 but would have been subsequently destroyed or buried1 becoming in the latter case1 submorainic4 ,this would be likely to be the fate of all such superglacial gravels as reached the edge of the ice up to the time of its maximum advance4 ,streams descending from the surface of the ice into crevasses also must have carried down sand and gravel where such materials existed on the ice4 ,these deposits may have been made on the rock which underlies the drift1 or they may have been made on stratified or unstratified drift already deposited4 ,in either case they were liable to be covered by till1 thus reaching an inter-till or sub-till position4 ,englacial streams probably do little depositing1 but it is altogether conceivable that they might accumulate such trivial pockets of sand and gravel as are found not infrequently in the midst of till4 ,the inter-till position would be the result of subsequent burial after the stratified material reached a resting place4 ,complexity of relations4--,from the foregoing it becomes clear that there are diverse ways by which stratified drift1 arising in connection with an ice sheet1 may come to be interbedded with till1 when due recognition is made of all the halts and oscillations to which the edge of a continental glacier may have been subject during both its advance and retreat4 ,,classification ,,of ,,stratified ,,drift ,,on ,,the ,,basis ,,of ,,position4 ,in general the conditions and relations which theoretically should prevail are those which are actually found4 ,on the basis of position stratified drift deposits may be classified as follows3 #a4 ,extraglacial deposits1 made by the waters of any glacial epoch if they flowed and deposited beyond the farthest limit of the ice4 #b4 ,supermorainic deposits1 made chiefly during the final retreat of the ice from the locality where they occur1 but sometimes by extraglacial streams or lakes of a much later time4 ,locally too1 stratified deposits of an early stage of a glacial epoch1 lying on till1 may have failed to be buried by the subsequent passage of the ice over them1 and so remain at the surface4 ,in origin1 supermorainic deposits were for the most part extraglacial 7including marginal71 so far as the ice sheet calling them into existence was concerned4 ,less commonly they were subglacial1 and failed to be covered1 and less commonly still superglacial4 #c4 ,the submorainic 7basal7 deposits were made chiefly by extraglacial waters in advance of the first ice which affected the region where they occur4 ,they were subsequently overridden by the ice and buried by its deposits4 ,submorainic deposits1 however1 may have arisen in other ways4 ,subglacial waters may have made deposits of stratified drift on surfaces which had been covered by ice1 but not by till1 and such deposits may have been subsequently buried4 ,the retreat of an ice sheet may have left rock surfaces free from till covering1 on which the marginal waters of the ice may have made deposits of stratified drift4 ,these may have been subsequently covered by till during a re-advance of the ice in the same epoch or in a succeeding one4 ,still again1 the till left by one ice sheet may have been exposed to erosion to such an extent as to have been completely worn away before the next ice advance1 so that stratified deposits connected with a second or later advance may have been made on a driftless surface1 and subsequently buried4 #d4 ,intermorainic stratified drift may have originated at the outset in all the ways in which supermorainic drift may originate4 ,it may have become intermorainic by being buried in any one of the various ways in which the stratified drift may become submorainic4 ,,changes ,,in ,,drainage ,,effected ,,by ,,the ,,ice4 ,while the ,ice ,was on4 ,as the continental ice sheet invaded a region1 the valleys were filled and drainage was thereby seriously disturbed4 ,different streams were affected in different ways4 ,where the entire basin of a stream was covered by ice1 the streams of that basin were1 for the time being1 obliterated4 ,where the valley of a stream was partially filled with ice1 the valley depression was only partially obliterated1 and the remaining portion became the scene of various activities4 ,where the ice covered the lower course of a stream but not the upper1 the ice blocked the drainage1 giving rise to a lake4 ,where the ice covered the upper course of a stream1 but not its lower1 the lower portion was flooded1 and though the river held its position1 it assumed a new phase of activity4 ,streams issuing from the ice usually carry great quantities of gravel and sand1 and make deposits along their lower courses4 ,long continued glacial drainage usually results in a large measure of aggradation4 ,this was true of the streams of the glacial period4 ,where a stream flowed parallel or approximately parallel to the edge of the advancing ice it was sometimes shifted in the direction in which the ice was moving1 keeping parallel to the front of the ice4 ,all of these classes of changes took place in this region4 ,wisconsin lake4--,reference has already been made to certain lakes which existed in the region when the ice was there4 ,the largest of these lakes was that which resulted from the blocking of the ,wisconsin river4 ,the ice crossed its present course at ,kilbourn ,city1 and its edge lay to the west of the river from that point to ,prairie du ,sac 7see ,plate ,i74 ,the waters from the area now draining into the ,wisconsin must either have found an avenue of escape beneath the ice1 or have accumulated in a lake west of the edge of the ice4 ,there is reason to believe that the latter was what happened1 and that a great lake covered much of the low land west of the ,wisconsin river above and below ,kilbourn ,city4 ,the extensive gravel beds on the north flank of the quartzite bluff at ,necedah1 and the water-worn pebbles of local origin on the slope of ,petenwell peak 7,plate ,,xxxii71 as well as the gravels at other points1 are presumably the work of that lake4 ,the waters in this lake1 as in that in the ,baraboo valley1 probably rose until the lowest point in the rim of the basin was reached1 and there they had their outlet4 ,the position of this outlet has not been definitely determined1 but it has been thought to be over the divide of the ,black river4#h ,it is possible1 so far as now known1 that this lake was connected with that of the ,baraboo valley4 ,until topographic maps of this region are made1 the connections will not be easily determined4 #h ,chamberlin3 ,geology of ,wisconsin1 ,vol4 #a4 ,even after the ice had retreated past the ,wisconsin1 opening up the present line of drainage1 the lakes did not disappear at once1 for the ice had left considerable deposits of drift in the ,wisconsin valley4 ,thus at ,f1 ,plates ,,ii and ,,xxxvii1 and perhaps at other points1 the ,wisconsin has made cuts of considerable depth in the drift4 ,were these cuts filled1 as they must have been when the ice melted1 the drainage would be ponded1 the waters standing at the level of the dam4 ,this drift obstruction at ,f would therefore have prolonged the history of the lake which had come into existence when the ice blocked the drainage of the ,wisconsin4 ,as the drift of the valley was removed the level of the lake sank and finally disappeared4 ,baraboo lake4--,another lake which existed in this region when the ice was here1 occupied the valley of the ,baraboo and its tributaries when the ice blocked the valley at ,baraboo4 ,this lake occupied not only the valley of the ,baraboo1 but extended up the lower course of every tributary1 presumably rising until it found the lowest point in the rim of the drainage basin4 ,the location of this point1 and therefore the height of the lake when at its maximum1 are not certainly known1 though meager data on this point have been collected4 ,at a point three miles southeast of ,ablemans on the surface of a sandstone slope1 water-worn gravel occurs1 the pebbles of which were derived from the local rock4 ,on the slope below the gravel1 the surface is covered with loam which has a suggestion of stratification1 while above it1 the soil and subsoil appear to be the product of local rock decomposition4 ,this water-worn gravel of local origin on a steep slope facing the valley1 probably represents the work of the waves of this lake1 perhaps when it stood at its maximum height4 ,this gravel is about #abe feet 7aneroid measurement7 above the ,baraboo river to the north4 ,further evidence of a shore line has been found at the point marked ,t1 ,plate ,,ii4 ,at this place water-worn gravel of the local rock occurs in much the same relationship as that already mentioned1 and at the same elevation above the ,baraboo river4 ,at a point two and one-half miles southwest of ,ablemans there is local water-worn gravel1 with which is mingled glacial material 7pieces of porphyry and diabase7 which could have reached this point only by being carried thither by floating ice from the glacier4 ,the level of this mixed local and glacial material is 7according to aneroid measurement7 approximately the same as that of the other localities4 ,when the ice melted1 an outlet was opened via the ,lower narrows1 and the water of the lake drained off to the ,wisconsin by this route4 ,had the ice left no drift1 the lake would have been promptly drained when the ice melted2 but the lake did not entirely disappear immediately after the ice retreated1 for the drift which the ice left obstructed drainage to the east4 ,the moraine1 however1 was not so high as the outlet of the lake while the ice was on1 so that1 as the ice retreated1 the water flowed over the moraine to the east1 and drew down the level of the lake to the level of the lowest point in the moraine4 ,the postglacial cut through the moraine is about ninety feet deep4 ,besides being obstructed where crossed by the terminal moraine1 the valley of the ,baraboo was clogged to a less extent by drift deposits between the moraine and the ,lower narrows4 ,at one or two places near the ,city of ,baraboo1 such obstructions1 now removed1 appear to have existed4 ,just above the ,lower narrows 7c1 ,plate ,,xxxvii7 there is positive evidence that the valley was choked with drift4 ,here in subsequent time1 the river has cut through the drift-filling of the preglacial valley1 developing a passage about twenty rods wide and thirty-five feet deep4 ,if this passage were filled with drift1 reproducing the surface left by the ice1 the broad valley above it would be flooded1 producing a shallow lake4 ,the retreat of the ice therefore left two well defined drift dams in the valley1 one low one just above the ,lower narrows1 and a higher one1 the moraine dam1 just west of ,baraboo4 ,disregarding the influence of the ice1 and considering the ,baraboo valley only1 these two dams would have given rise to two lakes1 the upper one behind the higher dam being deeper and broader1 and covering a much larger area2 the lower one behind the lower dam1 being both small and shallow4 ,up to the time that the ice retreated past the ,lower narrows1 the waters of the upper and lower lakes were united1 held up to a common level by the ice which blocked this pass4 ,after the ice retreated past the ,lower narrows1 the level of the ,baraboo lake did not sink promptly1 for not until the ice had retreated past the site of the ,wisconsin was the present drainage established4 ,meantime the waters of the ,baraboo lake joined those of ,wisconsin lake through the ,lower narrows4 ,if the lakes had been before connected at some point farther west1 this connection through the narrows would not have changed the level of either4 ,if they were not before connected1 and if the ,wisconsin lake was lower than the ,baraboo1 this connection would have drawn down the level of the latter4 ,since the drainage from the ,baraboo went to the ,wisconsin1 the ,baraboo lake was not at first lowered below the level of the highest obstruction in the valley of the ,wisconsin even after the ice had retreated beyond that stream4 ,as the drift obstructions of the ,wisconsin valley were lowered1 the levels of all the lakes above were correspondingly brought down4 ,when the level of the waters in these lakes was brought down to the level of the moraine dam above ,baraboo1 the one ,baraboo lake of earlier times became two4 ,the level of the upper of these two lakes was determined by the moraine above ,baraboo1 that of the lower by the highest obstruction below the moraine in either the ,baraboo or ,wisconsin valley4 ,the drift obstructions in the ,baraboo valley were probably removed about as fast as those in the ,wisconsin1 and since the obstructions were of drift1 and the streams strong1 the removal of the dams was probably rapid4 ,both the upper and lower ,baraboo lakes1 as well as the ,wisconsin1 had probably been reduced to small proportions1 if not been completely drained1 before the glacial period was at an end4 ,devil's lake in glacial times4--,while the ice edge was stationary in its position of maximum advance1 its position on the north side of the main quartzite range was just north of ,devil's lake 7,plate ,,xxxvii74 ,the high ridge of drift a few rods north of the shore is a well defined moraine1 and is here more clearly marked than farther east or west1 because it stands between lower lands on either side1 instead of being banked against the quartzite ridge4 ,north of the lake it rises about #ge feet above the water4 ,when the ice edge lay in this position on the north side of the range1 its front between the ,east bluff and the ,devil's nose lay a half mile or so from the south end of the lake4 ,in this position also there is a well defined moraine4 ,while the ice was at its maximum stand1 it rose above these moraine ridges at either end of the lake4 ,between the ice at these two points there was then a notable basin1 comparable to that of the present lake except that the barriers to the north and southeast were higher than now4 ,the melting of the ice supplied abundant water1 and the lake rose above its present level4 ,the height which it attained is not known1 but it is known to have risen at least #ij feet above its present level4 ,this is indicated by the presence of a few drift bowlders on the ,west bluff of the lake at this height4 ,they represent the work of a berg or bergs which at some stage floated out into the lake with bowlders attached4 ,bowlders dropped by bergs might be dropped at any level lower than the highest stand of the lake4 ,other lakes4--,another glacial lake on the ,east quartzite bluff has already been referred to4 ,like the ,devil's lake in glacial time1 its basin was an enclosure between the ice on the one hand1 and the quartzite ridge on the other4 ,the location of this lake is shown on ,plate ,,xxxvii 7s74 ,here the edge of the ice1 as shown by the position of the moraine1 was affected by a re-entrant curve1 the two ends of which rested against the quartzite ridge4 ,between the ice on the one hand and the quartzite ridge on the other1 a small lake was formed4 ,its position is marked by a notable flat4 ,with the exception of the north side1 and a narrow opening at the northwest corner1 the flat is surrounded by high lands4 ,when the ice occupied the region1 its edge held the position shown by the line marking the limit of its advance1 and constituted an ice barrier to the north4#i ,the area of the flat was1 therefore1 almost shut in1 the only outlet being a narrow one at t1 ,plate ,,xxxvii4 ,if the filling of stratified drift which underlies the flat were removed1 the bottom of the area would be much lower than at present1 and much lower than the outlet at t4 ,it is therefore evident that when the ice had taken its position along the north side of the flat1 an enclosed basin must have existed1 properly situated for receiving and holding water4 ,since this lake had but a short life and became extinct before the ice retreated1 its history is here given4 #i ,the moraine line on the map represents the crest of the marginal ridge rather than its outer limit1 which is slightly nearer the lake margin4 ,stratified drift of the nature of overwash also intervenes at points between the moraine and the lake border4 ,at first the lake had no outlet and the water rose to the level of the lowest point 7t7 in the rim of the basin1 and thence overflowed to the west4 ,meanwhile the sediments borne in by the glacial drainage were being deposited in the lake in the form of a subaqueous overwash plain1 the coarser parts being left near the shore1 while the finer were carried further out4 ,continued drainage from the ice continued to bring sediment into the lake1 and the subaqueous overwash plain extended its delta-like front farther and farther into the lake1 until its basin was completely filled4 ,with the filling of the basin the lake became extinct4 ,the later drainage from the ice followed the line of the outlet1 the level of which corresponds with the level of the filled lake basin4 ,this little extinct lake is of interest as an example of a glacial lake which became extinct by having its basin filled during glacial times1 by sediments washed out from the ice4 ,near the northwest corner of this flat1 an exposure in the sediments of the old lake bed shows the curiously contorted layers of sand1 silt1 and clay represented in ,plate ,,xxxviii4 ,the layers shown in the figure are but a few feet below the level of the flat which marks the site of the lake4 ,it will be seen that the contorted layers are between two series of horizontal ones4 ,the material throughout the section is made up of fine-grained sands and clays1 well assorted4 ,that these particular layers should have been so much disturbed1 while those below and above remained horizontal1 is strange enough4 ,the grounding of an iceberg on the surface before the overlying layers were deposited1 the action of lake ice1 or the effect of expansion and contraction due to freezing and thawing1 may have been responsible for the singular phenomenon4 ,contorted laminae are rather characteristic of the deposits of stratified drift4 ,after the ,ice ,had ,disappeared4 ,as has already been indicated1 the irregular deposition of glacial drift gave rise to many depressions without outlets in which surface waters collected after the ice had disappeared1 forming ponds or lakes4 ,so abundant are lakes and ponds and marshes in recently glaciated regions and so rare elsewhere1 that they constitute one of the more easily recognized characteristics of a glaciated region4 ,after the ice had melted1 the mantle of drift which it left was sometimes so disposed as to completely obliterate preglacial valleys4 ,more commonly it filled preglacial valleys at certain points only4 ,in still other cases a valley was not filled completely at any point1 though partially at many4 ,in this last case1 the partial fillings at various points constituted dams above which drainage was ponded1 making lakes4 ,if the dams were not high enough to throw the drainage out of the valley1 the lakes would have their outlets over them4 ,the drift dam being unconsolidated would be quickly cut down by the outflowing water1 and the lake level lowered4 ,when the dam was removed or cut to its base1 the lake disappeared and drainage followed its preglacial course4 ,in case the valley was completely filled1 or completely filled at points1 the case was very different4 ,the drainage on the drift surface was established with reference to the topography which obtained when the ice departed1 and not with reference to the preglacial valleys4 ,wherever the preglacial valleys were completely filled1 the postglacial drainage followed lines which were altogether independent of them4 ,when preglacial valleys were filled by the drift in spots only1 the postglacial streams followed them where they were not filled1 only to leave them where the blocking occurred4 ,in the former case the present drainage is through valleys which are preglacial in some places1 and postglacial in others4 ,thus the drainage changes effected by the drift after the ice was gone1 concerned both lakes and rivers4 ,in this region there are several illustrations of these changes4 ,lakes4--,the lake basins of drift-covered regions are of various types4 ,some of them are altogether in drift1 some partly in drift and partly in rock1 and some wholly in rock4 ,basins in the drift were likely to be developed whenever heavy deposits surrounded thin ones4 ,they are especially common in the depressions of terminal moraines4 ,another class of lake basins occurs in valleys1 the basins being partly rock and partly drift4 ,if a thick deposit of drift be made at one point in a valley1 while above there is little or none1 the thick deposit will form a dam1 above which waters may accumulate1 forming a pond or lake4 ,again1 a ridge of drift may be deposited in the form of a curve with its ends against a rock-ridge1 thus giving rise to a basin4 ,in the course of time1 the lakes and ponds in the depressions made or occasioned by the drift will be destroyed by drainage4 ,remembering how valleys develop it is readily understood that the heads of the valleys will sooner or later find the lakes1 and drain them if their bottoms be not too low4 ,drainage is hostile to lakes in another way4 ,every stream which flows into a lake brings in more or less sediment4 ,in the standing water this sediment is deposited1 thus tending to fill the lake basin4 ,both by filling their basins and by lowering their outlets1 rivers tend to the destruction of lakes1 and given time enough1 they will accomplish this result4 ,in view of this double hostility of streams1 it is not too much to say that rivers are the mortal enemies of lakes4 ,the destruction of lakes by streams is commonly a gradual process1 and so it comes about that the abundance and the condition of the undrained areas in a drift-covered region is in some sense an index of the length of time1 reckoned in terms of erosion1 which has elapsed since the drift was deposited4 ,in this region there were few lakes which lasted long after the ice disappeared4 ,the basins of the ,baraboo and ,wisconsin lakes were partly of ice1 and so soon as the ice disappeared1 the basins were so nearly destroyed1 and the drift dams that remained so easily eroded1 that the lakes had but a brief history1--a history that was glacial1 rather than postglacial4 ,the history of the little lake on the ,east quartzite bluff as already pointed out1 came to an end while the ice was still present4 ,the beds of at least two other extinct ponds or small lakes above the level of the ,baraboo are known4 ,these are at v and w1 ,plate ,,xxxvii4 ,they owed their origin to depressions in the drift1 but the outflowing waters have lowered their outlets sufficiently to bring them to the condition of marshes4 ,both were small in area and neither was deep4 ,existing lakes4--,relatively few lakes now remain in this immediate region1 though they are common in most of the country covered by the ice sheet which overspread this region4 ,devil's lake only is well known4 ,the lake which stood in this position while the ice was on1 has already been referred to4 ,after the ice had melted away1 the drift which it had deposited still left an enclosure suitable for holding water4 ,the history of this basin calls for special mention4 ,at the north end of the lake1 and again in the capacious valley leading east from its south end1 there are massive terminal moraines4 ,followed southward1 this valley though blocked by the moraine a half mile below the lake1 leads off towards the ,wisconsin river1 and is probably the course of a large preglacial stream4 ,beyond the moraine1 this valley is occupied by a small tributary to the ,wisconsin which heads at the moraine4 ,to the north of the lake1 the head of a tributary of the ,baraboo comes within eighty rods of the lake1 but again the terminal moraine intervenes4 ,from data derived from wells it is known that the drift both at the north and south ends of the lake extends many feet below the level of its water1 and at the north end1 the base of the drift is known to be at least fifty feet below the level of the bottom of the lake4 ,the draining of ,devil's lake to the ,baraboo river is therefore prevented only by the drift dam at its northern end4 ,it is nearly certain also1 that1 were the moraine dam at the south end of the lake removed1 all the water would flow out to the ,wisconsin1 though the data for the demonstration of this conclusion are not to be had1 as already stated4 ,there can be no doubt that the gorge between the ,east and ,west bluffs was originally the work of a pre-,cambrian stream1 though the depth of the pre-,cambrian valley may not have been so great as that of the present4 ,later1 the valley1 so far as then excavated1 was filled with the ,cambrian 7,potsdam7 sandstone1 and re-excavated in post-,cambrian and preglacial time4 ,devil's lake then occupies an unfilled portion of an old river valley1 isolated by great morainic dams from its surface continuations on either hand4 ,between the dams1 water has accumulated and formed the lake4 ,changes in ,streams4 ,in almost every region covered by the ice1 the streams which established themselves after its departure follow more or less anomalous courses4 ,this region is no exception4 ,illustrations of changes which the deposition of the drift effected have already been given in one connection or another in this report4 ,skillett creek4--,an illustration of the sort of change which drift effects is furnished by ,skillett creek1 a small stream tributary to the ,baraboo1 southwest of the city of that name4 ,for some distance from its head 7a to b1 ,fig4 #dc7 its course is through a capacious preglacial valley4 ,the lower part of this valley was filled with the water-laid drift of the overwash plain4 ,on reaching the overwash plain the creek therefore shifted its course so as to follow the border of that plain1 and along this route1 irrespective of material1 it has cut a new channel to the ,baraboo4 ,the postglacial portion of the valley 7b to c7 is everywhere narrow1 and especially so where cut in sandstone4 ,the course and relations of this stream suggest the following explanation3 ,before the ice came into the region1 ,skillett creek probably flowed in a general northeasterly direction to the ,baraboo1 through a valley comparable in size to the preglacial part of the present valley4 ,as the ice advanced1 the lower part of this valley was occupied by it1 and the creek was compelled to seek a new course4 ,the only course open to it was to the north1 just west of the advancing ice1 and1 shifting westward as fast as the ice advanced1 it abandoned altogether its former lower course4 ,drainage from the ice then carried out and deposited beyond the same1 great quantities of gravel and sand1 making the overwash plain4 ,this forced the stream still farther west1 until it finally reached its present position across a sandstone ridge or plain1 much higher than its former course4 ,into this sandstone it has since cut a notable gorge1 a good illustration of a postglacial valley4 ,the series of changes shown by this creek is illustrative of the changes undergone by streams in similar situations and relations all along the margin of the ice4 ,illustration3 ,fig4 #dc4--,skillett ,creek1 illustrating the points mentioned in the text4 ,the picturesque glens 7,parfrey's and ,dorward's7 on the south face of the ,east bluff are the work of post-glacial streams4 ,the preglacial valleys of this slope were obliterated by being filled during the glacial epoch4 ,the ,wisconsin4--,the preglacial course of the ,wisconsin river is not known in detail1 but it was certainly different from the course which the stream now follows4 ,on ,plate ,i the relations of the present stream to the moraine 7and former ice-front7 may be seen4#aj ,as the ice approached it from the east1 the preglacial valley within the area here under consideration was affected first by the overwash from the moraine1 and later by the ice itself1 from the latitude of ,kilbourn ,city to ,prairie du ,sac4 #aj ,the preglacial course was probably east of the present in the vicinity of ,kilbourn ,city4 ,it has already been stated that the ice probably dammed the river1 and that a lake was formed above ,kilbourn ,city1 reaching east to the ice and west over the lowland tributary to the river1 the water rising till it found an outlet1 perhaps down to the ,black river valley4 ,when the ice retreated1 the old valley had been partly filled1 and the lowest line of drainage did not everywhere correspond with it4 ,where the stream follows its old course1 it flows through a wide capacious valley1 but where it was displaced1 it found a new course on the broad flat which bordered its preglacial course4 ,displacement of the stream occurred in the vicinity of ,kilbourn ,city1 and1 forced to find a new line of flow west of its former course1 the stream has cut a new channel in the sandstone4 ,to this displacement of the river1 and its subsequent cutting1 we are indebted for the far-famed ,dalles of the ,wisconsin4 ,but not all the present route of the river through the dalles has been followed throughout the entire postglacial history of the stream4 ,in ,fig4 #dd1 the depression ,a1 ,b1 ,c1 was formerly the course of the stream4 ,the present course between ,d and ,e is therefore the youngest portion of the valley1 and from its lesser width is known as the narrows4 ,during high water in the spring1 the river still sends part of its waters southward by the older and longer route4 ,the preglacial course of the ,wisconsin south of the dalles has never been determined with certainty1 but rational conjectures as to its position have been made4 ,the great gap in the main quartzite range1 a part of which is occupied by ,devil's lake1 was a narrows in a preglacial valley4 ,the only streams in the region sufficiently large to be thought of as competent to produce such a gorge are the ,baraboo and the ,wisconsin4 ,if the ,baraboo was the stream which flowed through this gorge in preglacial time1 the comparable narrows in the north quartzite range--the ,lower narrows of the ,baraboo--is to be accounted for4 ,the stream which occupied one of these gorges probably occupied the other1 for they are in every way comparable except in that one has been modified by glacial action1 while the other has not4 ,illustration3 ,fig4 #dd4--,the ,wisconsin valley near ,kilbourn ,city4 ,the ,baraboo river flows through a gorge--the ,upper narrows--in the north quartzite range at ,ablemans1 nine miles west of ,baraboo4 ,this gorge is much narrower than either the ,lower narrows or the ,devil's lake gorge1 suggesting the work of a lesser stream4 ,it seems on the whole probable1 as suggested by ,irving1#aa that in preglacial time the ,wisconsin river flowed south through what is now the ,lower narrows of the ,baraboo1 thence through the ,devil's lake gorge to its present valley to the south4 ,if this be true1 the ,baraboo must at that time have joined this larger stream at some point east of the city of the same name4 #aa ,irving4 ,geology of ,wisconsin1 ,vol4 ,,ii4 ,the ,driftless ,area4 ,reference has already been made to the fact that the western part of the area here described is driftless1 and the line marking the limit of ice advance has been defined4 ,beyond this line1 gravel and sand1 carried beyond the ice by water1 extends some distance to the west4 ,but a large area in the southwestern part of the state is essentially free from drift1 though it is crossed by two belts of valley drift 7valley trains7 along the ,wisconsin and ,mississippi rivers4 ,the driftless area includes1 besides the southwestern portion of ,wisconsin1 the adjoining corners of ,minnesota1 ,iowa and ,illinois4 ,in the earlier epochs of the glacial period this area was completely surrounded by the ice1 but in the last or ,wisconsin epoch it was not surrounded1 since the lobes did not come together south of it as in earlier times4 7,compare ,plate ,,xxxiii and ,fig4 #cf47 ,various suggestions have been made in the attempt to explain the driftless area4 ,the following is perhaps the most satisfactory3#ab #ab ,chamberlin and ,irving4 ,geology of ,wisconsin1 ,vols4 ,i and ,,ii4 ,the adjacent highlands of the upper peninsula of ,michigan1 are bordered on the north by the capacious valley of ,lake ,superior leading off to the west1 while to the east lies the valley of ,lake ,michigan leading to the south4 ,these lake valleys were presumably not so broad and deep in preglacial times as now1 though perhaps even then considerable valleys4 ,when the ice sheet1 moving in a general southward direction from the ,canadian territory1 reached these valleys1 they led off two great tongues or lobes of ice1 the one to the south through the ,lake ,michigan depression1 the other to the south of west through the ,lake ,superior trough4 7,fig4 #cf47 ,the highland between the lake valleys conspired with the valleys to the same end4 ,it acted as a wedge1 diverting the ice to either side4 ,it offered such resistance to the ice1 that the thin and relatively feeble sheet which succeeded in surmounting it1 did not advance far to the south before it was exhausted4 ,on the other hand1 the ice following the valleys of ,lakes ,superior and ,michigan respectively1 failed to come together south of the highland until the latitude of northern ,iowa and ,illinois was reached4 ,the driftless area therefore lies south of the highlands1 beyond the limit of the ice which surmounted it1 and between the ,superior and ,michigan glacial lobes above their point of union4 ,the great depressions1 together with the intervening highland1 are therefore believed to be responsible for the absence of glaciation in the driftless area4 ,contrast ,between ,glaciated and ,unglaciated ,areas4 ,the glaciated and unglaciated areas differ notably in 7#a7 topography1 7#b7 drainage1 and 7#c7 mantle rock4 #a4 ,topography4--,the driftless area has long been exposed to the processes of degradation4 ,it has been cut into valleys and ridges by streams1 and the ridges have been dissected into hills4 ,the characteristic features of a topography fashioned by running water are such as to mark it clearly from surfaces fashioned by other agencies4 ,rivers end at the sea 7or in lakes74 ,generally speaking1 every point at the bottom of a river valley is higher than any other point in the bottom of the same valley nearer the sea1 and lower than any other point correspondingly situated farther from the sea4 ,this follows from the fact that rivers make their own valleys for the most part1 and a river's course is necessarily downward4 ,in a region of erosion topography therefore1 tributary valleys lead down to their mains1 secondary tributaries lead down to the first1 and so on2 or1 to state the same thing in reverse order1 in every region where the surface configuration has been determined by rain and river erosion1 every gully and every ravine descends to a valley4 ,the smaller valleys descend to larger and lower ones1 which in turn lead to those still larger and lower4 ,the lowest valley of a system ends at the sea1 so that the valley which joins the sea is the last member of the series of erosion channels of which the ravines and gullies are the first4 ,it will thus be seen that all depressions in the surface1 worn by rivers1 lead to lower ones4 ,the surface of a region sculptured by rivers is therefore marked by valleys1 with intervening ridges and hills1 the slopes of which descend to them4 ,all topographic features are here determined by the water courses4 ,illustration3 ,fig4 #de4--;,drainage in the driftless area4 ,the absence of ponds and marshes is to be noted4 ,the relief features of the glaciated area1 on the other hand1 lack the systematic arrangement of those of the unglaciated territory1 and stream valleys are not the controlling elements in the topography4 #b4 ,drainage4--,the surface of the driftless area is well drained4 ,ponds and lakes are essentially absent1 except where streams have been obstructed by human agency4 ,the drainage of the drift-covered area1 on the other hand1 is usually imperfect4 ,marshes1 ponds and lakes are of common occurrence4 ,these types are shown by the accompanying maps1 ,figs4 #de and #df1 the one from the driftless area1 the other from the drift-covered4 ,illustration3 ,fig4 #df4--;,drainage in a glaciated region4 ,walworth and ,waukesha counties1 ,wisconsin1 showing abundance of marshes and lakes4 #c4 ,mantle rock4--,the unglaciated surface is overspread to an average depth of several feet by a mantle of soil and earth which has resulted from the decomposition of the underlying rock4 ,this earthy material sometimes contains fragments and even large masses of rock like that beneath4 ,these fragments and masses escaped disintegration because of their greater resistance while the surrounding rock was destroyed4 ,this mantle rock grades from fine material at the surface down through coarser1 until the solid rock is reached1 the upper surface of the rock being often ill-defined 7,fig4 #dg74 ,the thickness of the mantle is approximately constant in like topographic situations where the underlying rock is uniform4 ,the residual soils are made up chiefly of the insoluble parts of the rock from which they are derived1 the soluble parts having been removed in the process of disintegration4 ,illustration3 ,fig4 #dg4--,section in a driftless area1 showing relation of the mantle rock to the solid rock beneath4 ,with these residuary soils of the driftless area1 the mantle rock of glaciated tracts is in sharp contrast4 ,here1 as already pointed out1 the material is diverse1 having come from various formations and from widely separated sources4 ,it contains the soluble as well as the insoluble parts of the rock from which it was derived4 ,in it there is no suggestion of uniformity in thickness1 no regular gradation from fine to coarse from the surface downward4 ,the average thickness of the drift is also much greater than that of the residual earths4 ,further1 the contact between the drift and the underlying rock surface is usually a definite surface4 7,compare ,figs4 #cb and #dg47 ,,postglacial ,,changes4 ,since the ice melted from the region1 the changes in its geography have been slight4 ,small lakes and ponds have been drained1 the streams whose valleys had been partly filled1 have been re-excavating them1 and erosion has been going on at all points in the slow way in which it normally proceeds4 ,the most striking example of postglacial erosion is the dalles of the ,wisconsin1 and even this is but a small gorge for so large a stream4 ,the slight amount of erosion which has been accomplished since the drift was deposited1 indicates that the last retreat of the ice1 measured in terms of geology and geography1 was very recent4 ,it has been estimated at #g1jjj to #aj1jjj years1 though too great confidence is not to be placed in this1 or any other numerical estimate of post-glacial time4 ,,index4 ---------------------------------------- ---------- ,,pages ,ablemans #ff1fg ,baraboo ,lake #acj ,baraboo ,quartzite ranges #b1 #fe ,constitution of #ad ,dynamic action in #ae1 #ag1 #ah ,gaps in-- ,devil's ,lake ,gap #c1 #ac ,lower ,narrows #e1 #ac1 #fg ,narrows ,creek #ff ,upper ,narrows #e1 #aj1 #ag1 #ai1 #fg ,igneous rock in #ah ,structure of #ae ,topography of #e1 #ac ,base-level #dg ,base-level plains #ej ,bowlder clay #ig ,breccia #ah ,castle ,rock #ga ,cleopatra's ,needle #fe ,cold ,water ,canyon #gj ,conglomerate #aj1 #bh ,basal 7,potsdam7 #bi ,corrasion #cf ,cross-bedding #cj ,cycle of erosion #dd1 #dg ,dalles of the ,wisconsin #fi ,origin of #ec ,scenery of #fi1 #adj ,dell ,creek #ec ,deltas #cj1 #ef1 #abj ,deposits-- ,by extra-glacial waters #aae-abc ,by ice #he1 #id ,by rivers #ee1 #ef ,by subglacial streams #abd ,of drift classified #abg ,devil's ,doorway #fe ,devil's ,lake #acb ,history of #acb ,in glacial times #acb ,location #c1 #i ,origin of #acb ,devil's ,nose #e1 #aaj ,divides1 ,shifting of #dd ,dorward's ,glen #aj1 #ad1 #bi1 #fh ,drift #gc ,characteristics of #if ,constitution of #id ,deposits classified #abg ,effect on topography #he1 #hh ,relation of stratified to unstratified #abe ,stratified #aaa ,topography of #aja1 #ajc ,driftless area #gi1 #adb ,drainage-- ,adjustment of #fb ,changes in1 effected by the ice #abh1 #adb ,establishment of #fa ,glacial #aac ,of drift-covered area #add ,of driftless area #add ,postglacial changes in #adf ,endmoraene #ajh ,erosion-- ,by rain1 and rivers1 general outline of #cf-eh ,elements of #cf ,of folded strata #ej ,of rocks of unequal hardness #dg ,of the quartzite #be ,preglacial #fj ,topography #ab ,without valleys #cg ,eskers #abd ,falls #dh ,fossils-- ,in limestone #ab ,in sandstone #i1 #aa ,friendship mounds #ga ,geographic features1 general #c-bj ,glacial drainage #aac ,glaciated area #gh1 #ia1 #adc ,glacier ice-- ,deposition by #he ,direction of movement #hh ,erosive work of #gi-hd ,formation of #gd ,movement of1 affected by topography #hi ,glens #fh ,green ,bay lobe #ia ,gibraltar rock #fc ,ground ,moraine-- ,constitution of #ii ,location of #ig ,topography of #aja ,groundwater level #da ,ice sheets-- ,formation of #gd ,history of #aad ,movement of #ge1 #hh ,north ,american ice sheet #gh ,igneous rock #ah ,intermittent streams #db ,kames #aae ,lakes-- ,wisconsin ,lake #abi ,baraboo ,lake #acj ,devil's ,lake #c1 #i1 #acb1 #acg ,limestone1 see ,lower ,magnesian4 ,lower ,magnesian limestone-- ,fossils of #ab ,history of #ca-cb ,occurrence of #aa ,origin of #aa ,position of #ab ,structure of #h ,lower ,narrows #e1 #ac1 #fg ,mantle rock #bj1 #add ,metamorphism #ad1 #bd ,monadnocks #ea ,moraines 7see terminal moraine and ground moraine74 ,morainic aprons #aai ,narrows #di ,in quartzite #ff1 #fg ,natural bridge #fi ,navy ,yard #fi ,niagara limestone #cc ,north ,american ice sheet #gh ,nunatak #hi ,osars 7see ,eskers74 ,outwash plains #aah1 #abj ,overwash plains #aah1 #abj ,parfrey's ,glen #aj1 #ad1 #bi1 #fh ,peneplain #dg1 #ej ,pewit's nest #i1 #ec1 #fi ,pine ,hollow #fi ,postglacial changes #adf ,potsdam sandstone-- ,fossils of #i1 #aa ,history of #bg-ca ,origin of #i-aa ,relation to quartzite #ai ,structure of #h ,quartzite 7see also ,baraboo quartzite ranges7-- ,dynamic ,metamorphism of #bd ,erosion of #be ,origin of #bc ,submergence of #bg ,thickness of #bf ,uplift of #bd ,rapids #dh ,rejuvenation of streams #ef ,ripple marks #i1 #ae ,roches moutonnee #ha ,sandstone 7see ,potsdam and ,st4 ,peters74 ,sauk ,prarie #aag1 #aah1 #aai ,skillett ,creek #h1 #ec1 #ach ,slope of upper surface of ice #aaa ,snow fields #gd ,soil #g1 #add1 #adf ,stand rock #gj ,steamboat rock #gj ,st4 ,peter's sandstone #cb ,stratified drift #aaa-aab1 #abe ,streams1 changes in #ach ,subaqueous overwash plains #abj ,subglacial till 7ground moraines7 #ii ,sugar ,bowl #gj ,talus slopes #fe ,terminal moraines-- ,across the ,united ,states #gh ,development of #ajb ,in ,devil's ,lake region #aje ,boundaries of #ajf ,location of #ib1 #ic1 #ajh ,on the main quartzite range #ajg ,width of #ajf ,topography of #ajc ,till #ig ,topography-- ,effect of1 on ice movement #hi ,erosion topography #ab ,of drift-covered country #h1 #adc ,of driftless area #f1 #g1 #ab1 #adc ,of plain surrounding quartzite ridge #f ,of quartzite ridges #e ,transportation by streams #ee ,tributary valleys #ci ,turk's ,head #fe ,unconformity #ai ,underground water #eh ,unglaciated areas #gi1 #adb1 #adc ,unstratified drift #ii1 #ajb1 #abe ,upper ,narrows #e1 #aj1 #ag1 #ai1 #fg ,valley1 the-- ,beginning of #cg ,characteristics of1 at various stages #eb-ed ,course of #ci ,how a valley gets a stream #dj ,limits of #dc ,valley trains #aaf ,waterfalls #dh ,weathering #cf ,webster's ,prarie #aai ,wisconsin ,lake #abi ,wisconsin ,river #aci ,witch's ,gulch #gj