The Cretaceous deposits of Iowa, from time to time, have received the attention of a number of geologists. The most important researches were made by Marcou, Meek, Heer, White and Calvin. Their investigations were carried on chiefly in the vicinity of Sioux City. The formation elsewhere in the State has, with a few exceptions, received no consideration. Its exact extent is yet to be determined; its vertical thickness is yet unknown; the relative ages of some of its beds remain to be established

Lonsdale, E. H.

English

University of Northern Iowa

Proceedings of the Iowa Academy of Science Volume 1 Part 4, 1893; (1887) - Article 16 1893 Southern Extension of the Cretaceous in Iowa E. H. Lonsdale Copyright ©1893 Iowa Academy of Science, Inc. Follow this and additional works at: https://scholarworks.uni.edu/pias Recommended Citation Lonsdale, E. H. (1893) "Southern Extension of the Cretaceous in Iowa," Proceedings of the Iowa Academy of Science, 1(Pt. 4), 39-43. Available at: https://scholarworks.uni.edu/pias/vol1/iss4/16 This Research is brought to you for free and open access by the Iowa Academy of Science at UNI ScholarWorks. It has been accepted for inclusion in Proceedings of the Iowa Academy of Science by an authorized editor of UNI ScholarWorks. For more information, please contact scholarworks@uni.edu. IOWA ACADEMY OF SCIENCES. 39 SOUTHEHN EXTENSION OF THE CRETACEOUS IN IOWA. BYE. IT. LONSDALJ<;. The Cretaceous deposits of Iowa, from time to time, have received the attention of a number of g<,Qlogists. The most important researches were made by Marcou, Meek, Heer, White and Calvin. Their investigations were carried on chiefl.v in the vicinity of Sioux City. The formation elsewhere in the State has, with a few exceptions, received no corniider<ttion. Its exact extent is yet to be determined; its vertical thickness is yet unknown; the .rnlative ages of some of its beds remain to be established. Over western Iowa, in fact, ornr practically the whole State, resting upon the pre-tertiary ucds, whatever these bects may be, is a mantle of debris collected and carriell by the great glaciers as they advanced and receded, then and in thr: cnrl depositing· tirnt material which is now recognilo;ed as drift clays, sands, gravels and boulders. This drift material, as a whole, commonly so extensive in vertical thick-ness, so persistent in its occurrence, and so readily yielding to the weathering agencies, has almost completely concealed the older rocks upon which it traveled and deposited itself. There are, however, occasional exposures of these rocks standing out more or less precipitously along preglacial streams which were of such magnitude or position, as the case may be, to withstand the attack made by the glaciers, and thercb~ continue their existence; along postglacial water courses which have cut through the drift and upper strata of the underlying formations thus developing a narrow or broad channol and growing new exposures along its way. These few outcroppings afford about the only source from which reliable geological results can be gathered. The Cretaoeous, made up as it is of soft layers, such as sandstones, whose particles are commonly loosely or not cemented together, and beds of clay shales, wonld naturally snffer to a llreatcr exLent from the effects of the glaciers and weathering than would the limestones and other hard rocks of older fornrntious. It woult! consequently be expected that the limits of the former would not now be ernn approximately the same as the original restriction of the Cretaceous in Iowa, nor, as nearly the same as are the boundaries of the earlier formations. Again, on aecount of the texture of the Cretaceons the exposures soon became covered with debris, even though at the close of the glacial period they were yet bare. Therefore, only rarely will faces of rocKs be left to view. This is the case not only inland but along the bluffs of large and small streams. White has probably given more attention to the inland exposures of Cretaceous than any one else. In addition to the Sioux City region he 1Lonsdale: Southern Extension of the Cretaceous in IowaPublished by UNI ScholarWorks, 189340 10\VA ACADEMY OF SCIENCES. described beds in situ, in Guthrie and some of the southwestern counties and set them down as Cretaceous. To thobe in Montgomery county, con-sisting of almost wholly of ferruginous grits, he gave the name Nishnabotna sandstone. The exposures farthest to the southeast were located in Guthrie county; the southernmost at Red Oak, Montgomery county. These are all described as outliers, the distance from the assumed eastern and southern limits of the rnam Iowa Cretaceous deposits. of which the Sioux City beds form by far the most important adjunct, varying from twenty to nearly one hundred miles. In individual size these outliers have been considered as only a few miles, perhaps one to less than twenty, in their greatest diameter. Duriug the fielrl season wbieh has recently closed a considerable amount of work was done in southwestern Iowa; additional information pertaining to the Cretaceous outliers in genernl, was secured; the southern limit was extended and conclusions pertaining to areal mileage of the different outliers have been drawn with greater or less satisfaction. Jn the first place let the topography of southwestern Iowa be considered briefly. Eastward from the bluffs which are prevalent along the great flood plain of the Missouri or adjac~ent to the river itself the counties consist of gently rolling uplands, which rise gradually to a height of one hundred to two hundred feet above the near by waterways. The tops of the ridges between the usually parallel streams continue in their axial lines in an almost unbroken plane for many miles. The bottom, level land next to the larger streams varies in widlh from a few yards to one or two miles, this width depending largely upon the size of the stream which penetrates the low land. From the outer margins of these bottoms there rise gradual slopes curving smoothly to the upland llrainage lines. Occasionally are fount! outcroppings of bedded rock in these slopes but they are in no wise extensive in any locality. There are, however, in westeru Iowa beds of the Coal Measures which are exposed, but rarely are any such beds exposed at a great distance above the streams nenr which they are situated. The top of many are but a foot or so ~tbove the water, others tifty or possibly more; but those approximating the former in extent predominate. ln tlIP vicinity of the Cretaceous outliers this is even so and such occurrences would undoubtedly indicate if not certainly prove that these inland streams have cut through friable beds of the Cretaceous and but only a few of the upper beds of the hard Coal Measures, that possi!Jly not unfrequently has the former formation not been passed thro11gh by the streams now existing anti some of the so-called outliers are connected and not separated as here-tofore supposed. The fact that the drift, though omnipresent, in this sec-tion of the State is not excessively heavy, not heavy enough to hide pre-cipitous limestone bluil's, if they be of considerable thickness, makes this state of affairs more plausible. This condition seems even more probable in parts of Guthrie county where the bottom lan<ls are much narrower 1 han those to the southwest. Again, it is quite possible that these outliers in Montgomery and adjoining counties extend farther northward and those in Guthrie county farther northwestward, towanls the sources of and between the streams along which they lio; at the same time shortening the space intervening between the ouLliers and the present limits of the main Cre-taceous body in Iowa. Although no positive information can be given in support of this theory, the exposures being few in number and only adjacent 2Proceedings of the Iowa Academy of Science, Vol. 1 [1893], No. 4, Art. 16https://scholarworks.uni.edu/pias/vol1/iss4/16row A ACADEMY OF SCIENCES. 41 to the streams, one must readily infer that this condition exists at least to a greater degl'ee than heretofore accorded. It is a notable fact that between the Guthrie and Cass county outliers there are no exposures of bedded rock either of the Coal l\lettsu1·cs or of the Cretaceous and it may even he that one or more of these outliers in the one county are connected with those in the other. Further, as results of rnc(~nt ilffestig:itions, new or previously unrecorded, CL'etaceous outcrops luwe been fonnd; the southernmost deposits of this age are no longer coutinc<l to central :\Iontgomery and northeastern :\Iills countieg, In Montgomery connty along the western slope of the ridge lying ad,iaccnt to and east of the East ~islrnalJ1Jtna,, Cretaecons beds were recognized by an almost continuous exposure from Red Oak, the locality where White claimed the southernmost Cretaceous existed, to the south boundary of the county. The charactel' of the bed val'ies here from a tine white to brown non-iirrn sandrock to a compact pudding stone. This latter is composed largely of pebbles from one-fourth to one-half an inch in diameter, imbed-ded in a somewhat to quite siliceous Ji monite matrix. In some of these exposures are absorbed excellent samples of cross bed<ling. At Coburg, only one mile north of the south line of Montgomery county a bluff rises abruptly from the otttcr nrnrgiu of the here rather broad alluvial plain. Near the base of this bluff is a lwd of fine friable sandrock eighteen feet thick lying beneath a fow feet of coarser sand, small pebbles occnrring 111 bands, over which bed rests ahont ten feet from the pudding stone. This entire section presents an <~leg:wl cross bedded character. About half way between this point and Red Oak these same beds occur and are more folly exposed. The total exposed thickness of the lower sandstone is thirty feet while that of the ornrlying p1Hlding o-tone is perhaps as great. This latter rock is very hard and firmer than any Cretaceous rock yet noticed Ill Iowa, and is quite persistent in this vicinity, withstanding to a great degree the ernding agencies, so preserving the under deposits. Two and a half miles eastward from Coh.1rg, on the county line a soft, Cretaceous sandrock rises above lfamp creek forming on the south side of the creek a perpendicular bluff twenty feet in height. South of this bluff, in Page county, small outcrops of such stone arc noticed; some in the slope of the hill higher than the top of the bluff just mentioned. On the hill to the northward a well enternd the sandstone at an elevation some higher than that of the top of the creek hlnff. These facts go to prom tirnt the thick-ness of the lied lwrn is not mm:li less th:w it is found to be in northern Montgomery county. The, bottom of the bluff extends into the bed of the creek and only a short disl:rnc•' np the stream Coal Measure limestone crops out, with no 1rnreeptilile dip in any direction, several feet abo1'e the water, indicating again the uneunformability of the Cretaceous upon the lower rocks. In Page county ahont one mile east of Essex (Tp. 70 N., R. XXXIX \\'.) the pudding stone such as des('rihcHl elsewhere, is found exposetl along the roadside. Here it has about the same relati\'e position above the East Nishnabotna as at points farther northwanl. This outcrop is only twenty miles north of the Missouri line and is decidmlly the southernmost exposure of the formation recorded as existing in lo wa. South of this exposure 3Lonsdale: Southern Extension of the Cretaceous in IowaPublished by UNI ScholarWorks, 189342 IOWA ACADEMY OF SCIENCES. about five miles a well more than 300 feet deep was bored and no bed, definitely recognized as Cretaceous, was shown in the record; though it is possible that some of the upper clays there met were of this age. No samples of the borings were seen. It must be r<Jmembered that the surface of the Upper Carboniferous at the incursion of the Uretaceous sea in Iowa was not regular; perhaps even more irregular and broken than the surface of the strata is to-day. Deep channels, gorges, depressions, and rises marked the entire surface. The Cretaceous as a shore deposit may have wholly filled these Carboniferous channels and hollows, spreading itself in great depth near the floor, or partly leaving protuberances and ridges of higher ele\'ations uncovered. However this may have beeu, the friable Cretaceous was, after the time of its laying down, greatly moditied both by the preglacial weathering agen-cies and the glacial grinding and corroding. During those stages new channels were cut, others more deeply corroded, m~iuy extending through the entire thickness of the formation; large areas were disturbed, only to be obliterated by the repeate(l advancement and retreat of the glacier, and the high and low points were alike mantled with drift debris. The southern and southeastern limits, would, since the glaciers tra\'eled in a southeasterly direction, naturally be more altered than would other portions of this shore deposit, the original shore line would be wholly displaced and a new line, probably a number of miles northward, leH to n11rk the present irregular boundary. Thus it may be seen that the Cretaceous is not one persistent bed everywher'l of the same thickness with its boundary an unbroken line, and its character unvarying. Now extending from some of the outliers notice(l the topography presents itself, just as it appears at the outlier, semetimes for several miles in length. To cite a case, consider the outlier which is exposed at Coburg and in that vicinity. Here for several miles to the southwest, between the \Vest Tarkio and the East Nishuabotna rivers the upland topography such as at Coburg, continues without any abrupt change. Again, while no Cretaceous has been noted as occurring between the East Tarkio and the \Vest Nodaway rivers, the topography in Page county between these streams resembles, in many respects, that between those streams to the west, along which Gretaceous beds have been found in Montgomery county. It would appear, therefore, from surface features of this county, that the upland between these four streams are made up large!y of Cretaceous depos-its covered only by a mantle of drift. If this is so, it is probable that in the two counties lying in the most northwestern portion of Missouri, along the northern border, and through the entire length of Page county, Iowa. will be found jnst such beds of Cretaceous age as occur farther northward in the latter State. Additional examination of the region at hand may bring out definite results and prove that Cretaceous beds do now in reality exist in the donbtful localities jnst mentioned. In doing this work it must be borne in mind from what has been said, that because the topography appears so in any place it does not necessarily follow that under such topography rests the Cretaceous; the marginal shore deposits may have been so modified and the debris from the Ice age so unevenly laid down that the existence or non-existence of the Cretaceous can no longer be recognized by mere topographic features of the land surface. 4Proceedings of the Iowa Academy of Science, Vol. 1 [1893], No. 4, Art. 16https://scholarworks.uni.edu/pias/vol1/iss4/16IOWA ACADEMY OF scrn::-;;cEs. 43 Near Coburg the Crntaceous appears to be quite heavy, but if this forma-tion is found to externl southward and into Mh;souri where no areas, how-ever limited in extent, have yet beeu found, it would no doulit be quite thin unless in exceptionally rare cases, for towards the southern boundary of Page county the Carboniferous rocks are not infrequently found, where exposed, a considerable distance above the drainage line, the ridges are not more elevated above them nor the drift less thick upon the upland. Just how far the shore line of the Cretaceous sea extended southward cannot definitely be tigured now, but. considering the position and abun-dance of outliers to the south and southeast along the present border, the direction the glaciers advanced and the readiness with which the friable beds could be broken off and carried away, one can immediately conceive how this shore line and the main deposit have been extensively altered, and how the present southern boundary may be far northward of the southern shore-line of the then probably continuous deposit. For the present, however, it seems desirable to call the exposure near Essex at least very near the farthest south any Cretaceous in situ exists in Iowa; realizing at the sa111e time the possibility, if not probability, that such may yet be found southward and iu Missouri. The finding of Cretaceous boulrlers amongst the !lrift is by no means uncommon. At the foot of the Missouri bluffs near Henton, in Mills county, a number of irregularly shaped masses of pudding stone were secured. Those were qnite similar to the bedded stone in some of the coun-ties further eastwi1nl. Jnst across into l\lissonri from Blanchard, Iowa, on the bank of the \l\'csl Tarkio is, in a cut recently made, a fifteen-foot bed of more or less clayey sandstone doubtless Cretaceous in origin but modified on being removed and dcposite!l here IJy the glacier. It would not seem that this sand bed nor the pudding stone had been carried away any great distance from their place of original deposition but their sources are yet to be traced. TOPOGRAPHY OF THE GRANITE AND PORPHYlff REGION OF MISSOURI. BY E. H. LONSDALE. When speaking of the Archrnan hill,., of Missouri Pumpelly has likened them unto "an archipelago of islands in the Lower Silurian strata which surrounded them as a whole and separate them from one another." To one who knows this interesting territory with its isolated and grouped knobs hills and mountains of crystalline rocks standing out more or less promi-nently and dotting the broad expanse of more recent sedimentaries, this 1igure is an exceedingly happy one; one most admirably taken. In order to appreciate the picturesqueness of the scenery there presented it becomes requisite that not merely a binls-eye view be taken but also to 5Lonsdale: Southern Extension of the Cretaceous in IowaPublished by UNI ScholarWorks, 1893

Southern Extension of the Cretaceous in Iowa

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Southern Extension of the Cretaceous in Iowa

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