,geology of ,devils ,tower ,national ,monument ,wyoming ,by ,,charles ,s4 ,,robinson ,a ,,contribution ,,to ,,general ,,geology ,illustration3 ,,department ,,of ,,the ,,interior ,march #c1 #aidi ,the ,national ,park ,service and the ,devils ,tower ,natural ,history ,association wishes to thank the ,united ,states ,geological ,survey for their kind permission to have this ,bulletin reprinted with minor changes4 ,,contents ,page ,abstract #a ,introduction #a ,geology #c ,devils ,tower #c ,sedimentary rocks #f ,spearfish formation #f ,gypsum ,spring formation #g ,sundance formation #g ,stockade ,beaver shale member #h ,hulett sandstone member #h ,lak member #i ,redwater shale member #i ,stream terrace deposits and alluvium #aj ,talus and landslide material #aj ,structure #aa ,geologic history #aa ,origin of ,devils ,tower #ab ,selected bibliography #ac ,,illustrations ,,figure ,page #eb4--;,index map showing location of ,devils ,tower ,national ,monument #b #ec4;,a4--,northwest side of ,devils ,tower showing how the columns taper or converge and in places unite near the top and are cut by numerous cross-fractures #d ,b4--,southwest corner of ,devils ,tower showing the columns flaring out and merging to form the massive base #d #ed4--;,generalized section of the sedimentary rocks of the ,devils ,tower ,national ,monument #f ,a ,,contribution ,,to ,,general ,,geology ,,geology ,,of ,,devils ,,tower ,,national ,,monument1 ,,wyoming ,by ,charles ,s4 ,robinson ,,abstract ,devils ,tower is a steep-sided mass of igneous rock that rises above the surrounding hills and the valley of the ,belle ,fourche ,river in ,crook ,county1 ,wyo4 ,it is composed of a crystalline rock1 classified as phonolite porphyry1 that when fresh is gray but which weathers to green or brown4 ,vertical joints divide the rock mass into polygonal columns that extend from just above the base to the top of the ,tower4 ,the hills in the vicinity and at the base of the ,tower are composed of red1 yellow1 green1 or gray sedimentary rocks that consist of sandstone1 shale1 or gypsum4 ,these rocks1 in aggregate about #djj feet thick1 include1 from oldest to youngest1 the upper part of the ,spearfish formation1 of ,triassic age1 the ,gypsum ,spring formation1 of ,middle ,jurassic age1 and the ,sundance formation1 of ,late ,jurassic age4 ,the ,sundance formation consists of the ,stockade ,beaver shale member1 the ,hulett sandstone member1 the ,lak member1 and the ,redwater shale member4 ,the formations have been only slightly deformed by faulting and folding4 ,within #b1jjj to #c1jjj feet of the ,tower1 the strata for the most part dip at #c-e towards the ,tower4 ,beyond this distance1 they dip at #b-e from the ,tower4 ,the ,tower is believed to have been formed by the intrusion of magma into the sedimentary rocks1 and the shape of the igneous mass formed by the cooled magma is believed to have been essentially the same as the ,tower today4 ,devils ,tower owes its impressiveness to its resistance to erosion as compared with the surrounding sedimentary rocks1 and to the contrast of the somber color of the igneous column to the brightly colored bands of sedimentary rocks4 ,,introduction ,devils ,tower1 a mass of bare rock that rises abruptly from the surrounding grasslands and pine forests1 is one of the most conspicuous geologic features of the ,black ,hills region4 ,because of its scenic beauty and scientific interest1 ,president ,theodore ,roosevelt in #aijf established ,devils ,tower and a small surrounding area as the first ,national ,monument4 ,the ,devils ,tower ,national ,monument covers an area of about #b square miles near the center of ,crook ,county in northeastern ,wyoming 7fig4 #eb74 ,a paved road from the entrance of the ,national ,monument goes south #g miles to join ,u4 ,s4 ,highway #ad at a point #bi miles northwest of ,sundance1 ,wyo41 and #cc miles northeast of ,moorcroft1 ,wyo4 ,the entrance to the ,national ,monument may also be reached by a road 7paved in ,wyoming7 that goes northeastward from the entrance1 via ,hulett and ,aladdin1 ,wyo41 to ,belle ,fourche1 ,s4 ,dak41 a distance of about #ed miles1 where it joins ,u4 ,s4 ,highways #bab and #he4 ,illustration3 ,figure #eb4--;,index map showing location of ,devils ,tower ,national ,monument4 ,public campgrounds and a natural history museum are maintained by the ,national ,park ,service at the base of the ,tower about #c miles by paved road from the ,monument entrance4 ,the geology of the ,devils ,tower ,national ,monument was mapped during the summer of #aied by the ,u4 ,s4 ,geological ,survey in collaboration with the ,national ,park ,service4 ,the work was part of a study of the geology of the northern and western parts of the ,black ,hills region conducted by the ,survey on behalf of the ,division of ,raw ,materials of the ,u4 ,s4 ,atomic ,energy ,commission4 ,the author wishes to acknowledge the assistance of the ,national ,park ,service and1 in particular1 ,mr4 ,raymond ,mc,intyre1 ,superintendent of ,devils ,tower ,national ,monument4 ,,geology ,the rocks exposed in the ,devils ,tower ,national ,monument may be divided on the basis of their origin into two general types2 igneous and sedimentary4 ,the ,tower itself is composed of igneous rock2 that is1 rock formed directly by cooling and crystallization of once molten materials4 ,the rocks exposed in the remainder of the ,monument are sedimentary2 that is1 they were formed by the consolidation of fragmental materials derived from other rocks or accumulations of chemical precipitates that were deposited either on the floors of prehistoric seas or near the shores of such seas4 ,these rocks1 which crop out around the igneous mass1 are layers of shale1 sandstone1 siltstone1 mudstone1 gypsum1 and limestone4 ,devils ,tower owes its impressiveness to the differing rates of erosion of these rock types--the soft sedimentary rocks erode more easily than the hard igneous rock--and to the contrast of the somber color of the igneous column to the brightly colored bands of sedimentary rock that surround its base4 ,,devils ,,tower ,devils ,tower rises steeply for about #fjj feet from a broad talus slope at its base4 ,the top of the ,tower1 at an altitude of #e1aag feet1 is about #a1bgj feet above the ,belle ,fourche ,river4 ,the ,tower is about #hjj feet in diameter at the base4 ,the sides rise almost vertically from the base for a distance of from #dj to #ajj feet and then slope in more gently to form a narrow bench4 ,above this bench1 the sides again rise steeply1 at angles of #ge to over #he1 to within about #ajj feet of the top where the angle becomes less steep and the top edge of the ,tower is somewhat rounded4 ,the top of the ,tower is almost flat and measures about #ahj feet from east to west and about #cjj feet from north to south4 ,one of the most striking features of the ,tower is its polygonal columns 7fig4 #ec74 ,most of the columns are #e sided1 but some are #d and #f sided4 ,the larger columns measure #f to #h feet in diameter at their base and taper gradually upward to about #d feet at the top4 ,the columns are bounded by well-developed smooth joints in the middle part of the ,tower1 but as the columns taper upward1 the joints between them1 rather than being smooth1 may be wavy and some of the columns may unite4 ,numerous cross-fractures in the upper part of the ,tower divide the column into many small irregularly shaped blocks 7fig4 #ec;,a74 ,illustration3 ,figure #ec4--;,a4 ,northwest side of ,devils ,tower showing how the columns taper or converge and in places unite near the top and are cut by numerous cross-fractures4 ,illustration3 ,figure #ec4--;,b4 ,southwest corner of ,devils ,tower showing the columns flaring out and merging to form the massive base4 ,the columns in the central and upper parts of the ,tower are almost vertical but flare out at the bench about #ajj feet above the base 7fig4 #ec;,b74 ,on the southwest side the columns are nearly horizontal4 ,where the columns flare out1 several columns may join to form a larger1 less distinct column that merges with the massive base4 ,at the base of the tower1 below the bench1 the rock is massive and jointing1 poorly developed4 ,here the joints form large irregularly shaped blocks rather than columns4 ,columnar joints form as the result of contraction within a rock mass4 ,in igneous rock the contraction is the result of cooling2 that is1 the cold solidified rock requires less volume than the same rock when molten4 ,as a rock cools it contracts1 and the resulting tension is in a plane parallel to the cooling surface4 ,when rupture takes place1 three fractures radiate from numerous centers in the plane parallel to the cooling surface4 ,ideally1 the fractures are at #abj to each other4 ,if the centers were evenly distributed1 the fractures from different centers would join forming hexagonal 7#f sided7 columns4 ,these fractures will go deeper and deeper into the rock as cooling progresses4 ,this condition because of many factors1 is seldom attained in nature1 so the columns may have #d1 #e1 #f1 or even more sides4 ,the rock making up ,devils ,tower is classified as phonolite porphyry 7,darton and ,o',harra1 #aijg1 p4 #f7 and is of ,tertiary age4 ,the fresh specimens have a light- to dark-gray or greenish-gray very fine-grained groundmass with conspicuous crystals of white feldspar--commonly about one-fourth to one-half inch in diameter--and smaller very dark-green crystals of pyroxene4 ,on the weathered surfaces the phonolite porphyry is a light gray or brownish gray4 ,lichens growing on the rock may give it a green1 yellowish-green1 or brown color4 ,using a microscope1 ,albert ,johannsen 7,darton and ,o',harra1 #aijg1 p4 #f7 identified the feldspar crystals as a soda-rich orthoclase and the pyroxene crystals as augite with an outer zone of aegirite4 ,in addition1 phenocrysts of apatite and magnetite1 were identified4 ,the groundmass1 according to ,johannsen1 consists of orthoclase laths in subparallel arrangement1 needles of aegirite1 possibly some nephelite1 small cubes of magnetite1 and secondary minerals of calcite1 kaolin1 chlorite1 analcite1 and a anisotropic zeolite4 ,illustration3 ,figure #ed4--;,generalized section of the sedimentary rocks of the ,devils ,tower ,national ,monument4 ,system ,series ,formation and member2 ,thickness1 in feet2 ,columnar section2 ,description ,,jurassic ,upper ,jurassic ,sundance formation ,redwater shale member2 #ajj2 ,gray and gray-green shale4 ,thin fine-grained sandstones in lower part2 thin fossiliferous limestones in upper part ,lak member2 #dj-fe2 ,yellow soft fine-grained calcareous sandstone ,hulett sandstone member2 #fj-gj2 ,yellow massive fine-grained calcareous sandstone ,stockade ,beaver shale member2 #he-ajj2 ,gray and gray-green shales with thin calcareous sandstones ,,unconformity ,middle ,jurassic ,gypsum ,spring formation2 #ae-ce2 ,white massive gypsum interbedded with thin red mudstone ,,unconformity ,,triassic ,spearfish formation2 #ajj2 ,red to maroon siltstone and sandstone interbedded with some thin shale ,,sedimentary ,,rocks ,the sedimentary rocks that surround ,devils ,tower have a total exposed thickness of about #djj feet4 ,they are divided1 from oldest to youngest1 into the ,spearfish formation of ,triassic age1 the ,gypsum ,spring formation of ,middle ,jurassic age1 and the ,sundance formation of ,late ,jurassic age 7fig4 #ed74 ,,spearfish ,,formation ,the ,spearfish formation crops out in the southern and northeastern parts of the ,devils ,tower ,national ,monument along the valley of the ,belle ,fourche ,river and its tributaries and forms conspicuous brownish-red to maroon cliffs that border the ,belle ,fourche valley for several miles in the ,devils ,tower region4 ,the formation is #dej to #fjj feet thick in the northern ,black ,hills area 7,darton1 #aiji1 p4 #bh72 however1 only the uppermost #ajj feet are exposed within the ,national ,monument4 ,the ,spearfish formation consists of red to maroon siltstone and sandstone interbedded with mudstone or shale4 ,locally1 greenish-blue shale partings are found in the siltstone and sandstone4 ,the formation is poorly cemented and weathers very easily forming1 for the most part1 gentle slopes1 as on the northeast and southwest sides of the monument4 ,where it does form cliffs1 as south of the ,tower1 the cliffs are cut by many sharp gullies4 ,no fossils have been found in the ,spearfish formation in the ,devils ,tower region1 but elsewhere in ,wyoming1 stratigraphically equivalent rocks contain land vertebrates of ,triassic age4 ,,gypsum ,,spring ,,formation ,the ,gypsum ,spring formation is exposed in a thin but almost continuous band around the ,tower on the southwest to northeast sides4 ,it also crops out near the top of the small hill at the eastern boundary of the ,national ,monument1 a few hundred feet north of the ,registration ,building4 ,this formation is composed mostly of white gypsum1 which stands out conspicuously between the red beds of the underlying ,spearfish formation and beds of gray-green shale at the base of the overlying ,sundance formation4 ,the ,gypsum ,spring formation ranges in thickness from about #ae to about #ce feet4 ,it is thickest on the hill at the eastern boundary of the ,monument4 ,here the formation is made up of a lower unit consisting of a bed of white massive gypsum #bj feet thick overlain by #ad feet of interbedded white gypsum and dark-maroon mudstone4 ,the formation is #ae feet thick along the cliff directly south of ,devils ,tower4 ,at this place1 the formation consists of #ab feet of white massive gypsum interbedded with #a-f inch thick beds of dark-maroon mudstone overlain by #c feet of dark-brownish-red mudstone4 ,the differences in thickness are primarily the result of erosion of the ,gypsum ,spring formation prior to the deposition of the ,stockade ,beaver shale member of the ,sundance formation 7,imlay1 #aidg1 p4 #bdc74 ,,sundance ,,formation ,the ,sundance formation consists of an alternating sequence of greenish-gray shale1 light-gray to yellowish-brown sandstone and siltstone1 and gray limestone4 ,the formation crops out above the gypsum and red shale of the ,gypsum ,spring formation on the bluffs and low rolling hills that surround the ,tower4 ,the formation consists of four members that are1 in order of age from oldest to youngest1 the ,stockade ,beaver shale member1 the ,hulett sandstone member1 the ,lak member1 and the ,redwater shale member 7fig4 #ed7 7,imlay1 #aidg1 p4 #bbg-bgc74 ,stockade ,beaver shale member4--,in general1 this member1 because it is composed mostly of shale1 is poorly exposed4 ,the best exposures of the lower part are on the hill at the east boundary of the ,monument and along the steep slope south of the ,tower4 ,the upper part is fairly well exposed on the south side of the ridge north of the ,tower1 near the north boundary of the ,monument4 ,the member has a thickness of #he to #ajj feet4 ,the composition differs considerably in detail from one exposure to another1 but in general it consists of gray-green shale with interbedded fine-grained calcareous sandstone4 ,at the base of the member1 at nearly all exposures1 is a thin sandstone1 #a to #bd inches thick1 containing black or dark-gray water-worn chert pebbles that have a maximum dimension of about #b inches4 ,above the basal sand1 the lower half of the member is composed mostly of gray-green shale1 which locally contains some interbedded fine-grained calcareous sandstone1 thin sandy and shaly limestone or dolomitic limestone1 and rarely thin beds of red mudstone4 ,the upper half of the member consists of dark-gray to gray-green shale with interbedded fine-grained calcareous sandstone that range from less than #a foot to #f feet in thickness4 ,the contact of the ,stockade ,beaver shale member with the overlying ,hulett sandstone member is gradational4 ,the sandstone becomes more abundant in the upper part of the ,stockade ,beaver shale1 and the contact between those two members is placed at that point where the sandstone makes up more than #ej percent of the rocks4 ,hulett sandstone member4--,the ,hulett sandstone member is resistant to weathering and forms a conspicuous1 almost vertical1 cliff that nearly encircles the ,tower4 ,this member ranges in thickness from about #fj to #gj feet4 ,the ,hulett sandstone member consists1 in general1 of massive fine-grained glauconitic calcareous sandstone4 ,it is typically yellow or brownish yellow but locally may be pink or red4 ,in the lower #e to #aj feet the sandstone is in beds from less than #a inch to #b feet thick separated by gray or greenish-gray shale partings of from less than #a inch to #f inches thick4 ,many of the sandstone beds at the base of the member are ripple marked4 ,the #ej to #fj feet in the middle of the member consists of massive beds that range in thickness from #e to #bj feet4 ,this portion is well cemented and forms the conspicuous cliff seen throughout the area4 ,the upper #e to #aj feet is thin bedded 7beds from less than #a inch to #f inches in thickness7 locally shaly1 and poorly cemented4 ,this grades upward into the overlying sandstone and siltstone of the ,lak member4 ,lak member4--,the ,lak member crops out above the cliff of ,hulett sandstone that almost encircles the ,tower1 and it underlies a broad rolling area in the northwestern part of the ,monument4 ,the member is rarely exposed because it is composed of soft sandstone and siltstone that usually weather to gentle slopes and become covered with vegetation4 ,the best exposure is on the steep hill east of the ,tower and northwest of the bridge across the ,belle ,fourche river4 ,this member is #fe feet thick a few hundred feet east of the ,tower1 but mapping within the ,monument and measured sections within a few miles of the ,monument indicate that the average thickness is about #de feet4 ,the ,lak member is typically poorly bedded soft1 very fine-grained calcareous sandstone and siltstone with a few thin gray-green sandy shale partings4 ,at the base and near the top of the member may be a few thin 7less than #a inch to #f inches thick7 well-cemented sandstone beds that form small ridges4 ,the sandstone and siltstone grade almost imperceptibly from one to the other4 ,the color ranges from light yellow brown and yellow to red4 ,in the ,devils ,tower area1 shades of yellow and yellowish brown are most common4 ,the contact of the ,lak with the overlying ,redwater shale member can be observed only in the exposure east of the ,tower4 ,here1 the upper #c feet of the ,lak is a yellowish-brown calcareous silty sandstone with a few discontinuous sandy shale partings 7less than #a inch thick71 and the lower #c feet of the overlying ,redwater shale consists of dark-gray-green shale with interbedded1 thin silty sandstone4 ,redwater shale member4--,this member encircles ,devils ,tower1 but at most places it is covered by talus from the ,tower4 ,even where it is not covered by talus1 it is poorly exposed4 ,it consists mostly of shale that weathers into gentle slopes1 which are usually covered by vegetation4 ,the ,redwater shale is partly exposed on ,fossil ,hill1 northwest of ,devils ,tower1 and on the hill in the northwest corner of the ,monument4 ,the best exposures are on ,fossil ,hill4 ,the top of the ,redwater shale member is not exposed within the limits of the ,monument2 consequently1 the thickness could not be determined4 ,in surrounding areas the ,redwater shale ranges in thickness from #aej to #aij feet4 ,it is at least #ajj feet thick on the hill in the northwest corner of the ,monument4 ,the ,redwater shale consists mostly of light-gray to dark gray-green soft shale4 ,in the lower #bj or #cj feet are beds of yellow soft sandstone1 #c inches to #b feet thick4 ,in the upper part1 ranging from #ej feet above the base to the top1 are lenticular beds of fossiliferous limestone #a inch to #d feet thick4 ,two such beds of fossiliferous limestone are exposed on ,fossil ,hill4 ,the ,sundance formation contains clams1 oysters1 belemnites 7squids71 and other marine fossils that establish its age as ,late ,jurassic 7,imlay1 #aidg1 p4 #bdd-bfd74 ,,stream ,,terrace ,,deposits ,,and ,,alluvium ,stream deposits 7alluvium7 are found in the valleys of the small streams around the ,tower and1 in particular1 in the valley of the ,belle ,fourche ,river1 that cuts across the southeast corner of the ,monument4 ,the deposits consist of unconsolidated gravel1 sand1 silt1 and mud4 ,along the ,belle ,fourche ,river1 northwest of the river and between it and the main road1 the river cut a terrace in the ,spearfish formation4 ,on the terrace were deposited gravel and sand4 ,,talus ,,and ,,landslide ,,material ,the talus and landslides are composed primarily of the material from the ,tower and the ,hulett sandstone4 ,talus from the ,tower forms a broad apron that completely surrounds the ,tower4 ,the talus extends from high on the shoulders of the ,tower down to and across the sedimentary rock4 ,locally1 landslides of this talus have extended through valleys in the sedimentary rock down almost to the level of the surrounding streams4 ,the talus from the ,tower is composed of fragments of the columns that range from a few inches in diameter to large sections of the columns as much as #h feet in diameter and #be feet long4 ,the cliff of ,hulett sandstone that surrounds the ,tower breaks off into rectangular blocks that form talus slopes at the base of the cliffs and locally large landslides down the hill below the cliffs4 ,these blocks of ,hulett sandstone range in size from a few inches to many feet in diameter4 ,the talus material from the ,tower has at several places overlapped the cliff of ,hulett sandstone and become mixed with the material from the cliff4 ,about #a1djj feet north of the ,tower are two patches of what is believed to be talus formed from sedimentary rocks that once surrounded the ,tower4 ,the talus consists of fragments of medium-grained brownish-white sandstone and1 what is apparently1 a highly silicified gray or white fine-grained quartzite4 ,the sandstone resembles that found in the ,lakota 7,darton and ,o',hara1 #aijg1 p4 #c7 that lies about #bjj feet stratigraphically above the ,redwater shale in the area west of the ,monument4 ,the sandstone and quartzite occur in angular blocks that range from less than #a inch to several feet in diameter4 ,the spaces between the blocks are filled with a yellowish or brownish-white sand4 ,the ,lakota sandstone at one time surrounded the ,tower and it is believed that these blocks are residual blocks that have not been removed by erosion4 ,,structure ,the sedimentary rocks in the ,national ,monument1 and in the surrounding area1 are gently folded into many small rolls1 basins and domes1 which locally are cut by faults of small displacement4 ,these small folds are superimposed on a large dome that is collapsed in the middle4 ,devils ,tower is near the middle of the collapsed dome4 ,from one-half to about a mile from the ,tower the sedimentary rocks dip gently from #b to #e away from the ,tower to form a broad dome4 ,within a radius of about #b1jjj to #c1jjj feet of the ,tower1 the dips change1 and the rocks dip1 in general1 from #c to #e towards the ,tower to form a shallow structural basin4 ,in the basin itself and on the dome are several small folds4 ,as an example1 ,spring ,no4 #a southwest of the ,tower is in the center of a comparatively sharp syncline or down-fold at the edge of the basin4 ,fossil ,hill northwest of the ,tower is another small structural basin4 ,the beds along the top and on the north side of ,fossil ,hill dip from #ab to #eb ,s4 ,those on the south side of the hill1 north of the road1 apparently dip very gently northward4 ,three faults were observed in the area of the ,national ,monument4 ,two of the faults are in the ,hulett sandstone west of the main road and west of the ,tower1 and the third is in the northwestern side of the ,tower near its base 7pl4 #cj74 ,the faults in the ,hulett sandstone are probably vertical1 and the displacement along them is believed to be less than #aj feet4 ,the fault at the base of the ,tower is a low-angle fault that trends northwesterly4 ,the attitude of this fault at the point where it disappears below the talus is3 strike1 ,n4 #da ,w42 dip1 #ba ,,ne4 ,the fault zone is #d to #ab inches wide and is filled with a yellowish-green clay and sheared fragments of altered phonolite porphyry4 ,the rock of the ,tower below this fault is somewhat altered2 the groundmass is a light greenish gray1 and the normally shiny crystals of feldspar have a dull earthy luster4 ,,geologic ,,history ,the geologic history of the ,devils ,tower area is part of that of the ,black ,hills region4 ,the uplift of the ,black ,hills and the subsequent erosion have exposed the rocks1 from which the geologic history of the area may be interpreted4 ,most of the rocks within the area around the ,black ,hills are composed of sediments deposited by water4 ,these sedimentary rocks1 which overlie much older rocks 7,precambrian71 were deposited in a series of successive layers during time intervals from the ,cambrian period to well into the ,tertiary period4 ,deposits in the ancient seas are represented by limestone1 shale and some sandstone2 deposits on low lands adjacent to seas1 as flood plains and deltas1 by sandstone1 siltstone1 and some mudstone2 and deposits along streams by conglomerate1 sandstone and siltstone4 ,between the periods of deposition were intervals when the land was relatively high1 and in certain areas all of the sediments of an earlier period were eroded away4 ,the oldest formation exposed in the ,national ,monument1 the ,spearfish formation1 was deposited during ,triassic time along flat lands bordering the sea4 ,arms of the sea locally invaded the area to leave deposits of gypsum1 which are found near the base of the ,spearfish in areas outside the ,national ,monument4 ,the ,gypsum ,spring formation was deposited in the sea in ,middle ,jurassic time following a period of uplift and erosion that occurred after the deposition of the ,spearfish formation4 ,after the ,gypsum ,spring formation was deposited1 the sea retreated1 and another period of erosion followed before ,late ,jurassic time when the sea invaded the area again and the ,sundance formation was deposited4 ,the depth and conditions for deposition in this sea changed from time to time1 as shown by the alternating beds of shale and sandstone in the ,sundance formation4 ,following the deposition of the ,sundance formation1 there were several periods when the area was above sea level and when the sea covered the area4 ,during the periods when it was above sea level1 the higher land was eroded1 and the sediments deposited at a lower level4 ,when the area was covered by the sea1 marine sediments1 principally shales1 were deposited4 ,near the end of the ,cretaceous period1 the sea made its final withdrawal1 and the sediments from late ,cretaceous time to the present were deposited in fresh water4 ,the ,black ,hills uplift developed primarily during early ,tertiary time1 although it may have started in very late ,cretaceous time4 ,at this time the present general structural features of the ,black ,hills area were developed1 and1 probably1 the igneous rocks1 such as ,devils ,tower1 were intruded 7,jaggar1 #aija1 p4 #bff74 ,following this1 the ,black ,hills area was repeatedly uplifted1 and erosion exposed the older sedimentary and intrusive rocks4 ,even today streams continue to strip more and more rock from the country1 leaving only local deposits1 such as alluvium and terrace deposits1 along the valleys4 ,,origin ,,of ,,devils ,,tower ,the origin of ,devils ,tower has been a matter of speculation for many years1 and even today after detailed geologic mapping of the area1 no conclusive proof of its mode of origin can be presented4 ,several theories of the origin have been proposed4 ,one of the more popular of these is that it is the neck of an extinct volcano 7,carpenter1 #ahhh2 ,dutton and ,schwartz1 #aicf74 ,another theory is that ,devils ,tower and ,missouri ,buttes 7a mass of the same type of rock about #d miles northwest of the ,tower7 are the remnants of a laccolith 7a tabular intrusive igneous body1 thickest in the middle1 and with a relatively level floor71 the vent for which was under ,missouri ,buttes 7,jaggar1 #aija1 p4 #bfd74 ,darton 7#aija1 p4 #fi7 believed that the ,tower is the remnant of a laccolith1 smaller than the one proposed by ,jaggar1 the feeding vent for which was underneath the ,tower4 ,much more detailed geologic work will have to be done in the surrounding area before the mode of origin of ,devils ,tower may be proved conclusively4 ,the evidence gathered during the present investigation1 however1 suggests that ,devils ,tower is a body of intrusive igneous rock1 which was never much larger in diameter than the present base of the ,tower1 and which at depth 7#a1jjj feet or more7 is connected to a sill or laccolith type body4 ,the bases for this theory are-- #a4 ,the exposed portion of the ,tower is the result of recent erosion4 ,at the time of its intrusion it was surrounded and probably covered by several hundred feet of sedimentary rock4 #b4 ,the mineral composition and texture are more typical of shallow intrusive rocks1 which are formed at depth1 than extrusive rocks1 which are formed on the surface4 #c4 ,no evidence of extrusive igneous activity has been found in the surrounding area4 #d4 ,missouri ,buttes1 about #d miles to the northwest1 and the ,tower have the same composition so it is assumed that they were derived from a common magma2 possibly the magma of a large intrusive body1 such as a laccolith or sill4 #e4 ,in a well drilled about #a miles southwest of ,missouri ,buttes1 near the center of a structural dome1 rock similar to the ,tower and ,missouri ,buttes was encountered at about #a1djj feet below the base of ,missouri ,buttes4 ,inasmuch as the thickness of the sedimentary rocks in this area is normally much greater than this depth1 the rock in the drill hole probably represents an intrusive body1 rather than the ,precambrian igneous rocks upon which the younger sedimentary rocks were deposited4 #f4 ,the relatively small amount of talus1 slope wash1 or terrace gravel derived from the ,tower and ,missouri ,buttes suggests that they have not been extensively eroded1 and therefore the original igneous bodies were not much larger than at present4 #g4 ,columnar jointing is common in intrusive bodies formed at comparatively shallow depths4 ,the following new material has been added to this booklet by the ,national ,park ,service 7,devils ,tower ,national ,monument1 #aihe7 ,the most recent in depth1 geologic study of ,devils ,tower was done by ,don ,l4 ,halverson 7#aihj7 and presented in a dissertation1 to the ,graduate ,faculty of the ,university of ,north ,dakota4 ,he stated that1 8,the ,missouri ,buttes and ,devils ,tower1 however1 are necks of extinct volcanoes which have been exposed by erosion4 ,this theory was first proposed by ,carpenter 7#ahhh7 and later expanded by ,dutton and ,schwartz 7#aicf74 ,the material which fed these volcanoes came from a minimum depth of #ah km4 ,evidence for this conclusion is listed in the following statements3 #a4 ,the alloclastic breccia in the vicinity of ,devils ,tower and the ,missouri ,buttes is definitely igneous in origin and probably represents periods of violent eruption4 #b4 ,a very definite similarity exists between these two features and the volcanic necks in the ,taylor ,mountain area of ,new ,mexico4 #c4 ,the distinctive columns with basal flare are also found in the volcanic necks of the ,taylor ,mountains 7,dutton and ,schwartz #aicf71 but have not been reported in columnar-jointed laccoliths4 #d4 ,the ,missouri ,buttes and ,devils ,tower were intruded directly through horizontal sediments without disrupting them1 even in the immediate vicinity of the igneous bodies4 #e4 ,recent research indicates that many of the laccolithic intrusions in the ,black ,hills region may have been less passive than previously considered4 ,sundance ,mountain may be a mixed volcanic cone consisting of welded ash fall1 massive quartz latite1 and ash flow tuffs4 ,nearby ,sugarloaf ,mountain is composed of layered tuffs 7,fashbough #aigi74 #f4 ,collapse of materials into partly evacuated reservoir chambers accounts for the depressions surrounding the ,missouri ,buttes and ,devils ,tower4 ,the #ij m of depression at the southern end of the ,buttes is difficult to explain with a laccolithic model4 #g4 ,flow directions deduced from oriented thin-sections and field observations indicate mostly vertical flow4 ,it must be noted that in both igneous bodies orientation of some grains is horizontal2 this could1 however1 simply indicate turbulent flow4 #h4 ,the stability field for the analcime-liquid system is #e kbar minimum 7,roux and ,hamilton #aigf71 which indicates that the original melt of ,devils ,tower and ,missouri ,buttes rock had to originate at a minimum depth of #ah km4 #i4 ,it is unlikely that magma which had ascended from great depths and had just penetrated the resistant ,hulett ,member of the ,sundance ,formation1 as well as the ,lakota and ,fall ,river ,formations1 would be stopped abruptly by the less resistant shales above4 ,when the magma reached the shale beds1 the weight of the column of igneous rock could have exceeded the strength of the shale1 causing the magma to flow horizontally4 ,no indication of horizontal spread1 however1 is observed4 ,the continuously cylindrical shape of the intrusions indicates that the magma moved steadily upward and probably reached the surface4 #aj4 ,carbonatites have been found1 and formally reported1 in the nearby ,bear ,lodge ,mountains1 and also as fragments in the alloclastic breccias of the ,missouri ,buttes4 ,their presence suggest a high volatile content for the magma and the possibility of explosive volcanism40 ,illustration3 #a4 ,illustration3 #b4 ,illustration3 #c4 ,,selected ,,bibliography ,carpenter1 ,f4 ,r41 #ahhh1 ,notes on the geology of the ,black ,hills3 ,preliminary report of the ,south ,dakota ,school of ,mines1 ,rapid ,city1 ,s4 ,dak4 ,darton1 ,n4 ,h41 #aiji1 ,geology and water resources of the northern portion of the ,black ,hills and adjoining regions in ,south ,dakota and ,wyoming3 ,u4 ,s4 ,geol4 ,survey ,prof4 ,paper #fe4 ,darton1 ,n4 ,h41 and ,o',harra1 ,c4 ,c41 #aijg1 ,description of the ,devils ,tower quadrangle1 ,wyoming3 ,u4 ,s4 ,geol4 ,survey ,geol4 ,atlas1 folio #aej4 ,dutton1 ,c4 ,e41 and ,schwartz1 ,g4 ,m41 #aicf1 ,notes on the ,jointing of the ,devil's ,tower1 ,wyoming3 ,jour4 ,geology1 v4 #dd1 no4 #f1 p4 #gag-gbh4 ,imlay1 ,r4 ,w41 #aidg1 ,marine ,jurassic of the ,black ,hills area1 ,south ,dakota and ,wyoming3 ,am4 ,assoc4 ,petroleum ,geologists ,bull41 v4 #ca1 no4 #b1 p4 #bbg-bgc4 ,jaggar1 ,t4 ,a41 ,jr41 #aija1 ,laccoliths of the ,black ,hills3 ,u4 ,s4 ,geol4 ,survey #bast ,ann4 ,report1 pt4 #c1 p4 #afc-bij4 ,pirsson1 ,l4 ,v41 #ahid1 ,on some phonolite rocks from the ,black ,hills3 ,am4 ,jour4 ,sci41 #c;d ser41 v4 #dg1 p4 #cda-cdf4 ,zuidema1 ,h4 ,p41 #aidh1 ,the touring public discovers ,mato ,tipi 7,devils ,tower1 ,wyo473 ,earth ,science ,digest1 v4 #c1 no4 #a1 p4 #c-g4 ,halverson1 ,d4 ,l41 #aihj1 ,geology and petrology of the ,devils ,tower1 ,missouri ,buttes and ,barlow ,canyon ,area1 ,crook ,county ,wyoming1 ,dissertation4 ,transcriber's ,notes --,publication information is from the original print copy--this e-text is public domain in the country of publication4 --,silently corrected palpable typos2 left non-standard spellings and dialect unchanged4 --,split single captions describing multiple images1 into multiple captions4 --,in the text versions1 delimited italics text in underscores 7the ,,html version reproduces the font form of the printed book47