In a report recently made to the State Geological Survey, the writer communicates in detail some facts regarding the brecciated zone of the Devonian in Linn county, Iowa, and the terranes subjacent. The following is in part a brief summary of this report

Norton, William Harmon

English

University of Northern Iowa

Proceedings of the Iowa Academy of Science Volume 1 Part 4, 1893; (1887) - Article 8 1893 Notes on the Lower Strata of the Devonian Series in Iowa William Harmon Norton Copyright ©1893 Iowa Academy of Science, Inc. Follow this and additional works at: https://scholarworks.uni.edu/pias Recommended Citation Norton, William Harmon (1893) "Notes on the Lower Strata of the Devonian Series in Iowa," Proceedings of the Iowa Academy of Science, 1(Pt. 4), 22-24. Available at: https://scholarworks.uni.edu/pias/vol1/iss4/8 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. 22 row A ACADEMY OF SCIENChS. At the town of Hot Springs some portions of the valley are occupied by horizontal beds of a Yery coarse conglomerate that lies unconformahly on the folded and tilted I{ed Beds. The thickness of the conglomerate is about forty feet. It is composed of fragments of all the harrler formations from the crystalline rocks at the center of the uplift to the purple limestone of the Red Beds and the quartzite of the Cretaceous. \Vhen the conglomerate was deposited the valley had essentially its present depth. In some places the streams have just fairly completed the work of cutting through the conglomerate, in other places they have cut twenty or thirty feet below its base. This conglomerate is prolmbly the equivalent of that lying at the base of the 'Vhite river Miocene. if so it would indicate an enormous amount of erosion between the beginning and mitlrlle of the Tertiary as compared with the amount accomplished since. Returning Jin ally to the main object for which these observations were undertaken, it is clear that Eennetlites dacotensis l\Iacbride, belongs to the Cretaceous perioll, and the evidence is practically conclusive that the exact horizon at which the individuals of the species were imbetlded is represented by the uppermost layers of the Dakota santi>tone. NOTES ON THE LOWER STRATA OF THE DEVONIAN SElUES IN IOWA. BY WILLIA}! HARMON NORTON. In a report recently made to the State Geological Survey, the writer com-nrnnicates in detrril somo facts regarding tho breeciated zoue of the Devonian in Linn county, Iowa, aud the terranes suhjacent. The following is in part a brief summary of this rnport: In the breccia which occupies the same horizon from Davenport to Fay-ette, and which has been termed by l\IcGee the Fayette breccia, four stageH are discriminated. The fourth, or upper stage, involves in Linn county to [t greater or less extent several life-zones of the Cellar Valley limestone, including the hor-izons of Acervularirt rlai:irlsoni (E. and H. ), Phil/ ipsastrea gigrts (Owen). Spir, ijera pennata (Owen), aiH\ Spir\ferrt dimesia! is rllall). J.\ilatrix and fragments are alike being fossiliferom; and shaly, and the fragments arc mmall_y large and often but sligl1tl_y disturbed. The third stage is distinguished by the predominance of fragmental masses, often large and rectangnlar, of a tough, grey, crystalline or semi-crystalline, !wavily bedded limestone, containing a distinet fauna, of which a large Uyroceras and Rhynchonella intermedia (B:trris) are the most charac-teristic fossils, and 0 ypirlula occidentrtlis !Hall) and Orth is nutcfrulandi (;\leek), the most common. The limestone of which these fragments is eom-posell is not found in place in Linn county. 1Norton: Notes on the Lower Strata of the Devonian Series in IowaPublished by UNI ScholarWorks, 1893IOWA ACADEMY OF SCIE~CES. 23 The second stage is defined by the abundance of fragments, usually small, of a hard, drab, unfossilifcrous limestone of finest grain, often thinly bedded, often finely lamirrntccl, the laminrn frcq1~ently being flexed or contorted. This limestone also is not found undisturbed in Linn county. The first stage is characterized by an abundant bu II or brown matrix, the fragments being sparse and small. Some of them are quartzose, b.elonging like the matrix to the subjacent terrane. This subjacent tcrrane, locally called the Kenwood beds, consists of mas-sive argillaceous and ferruginous buff and re<ldish-brown limestones, irreg-ularly bedded, often fkxe<I and arched ancl passing horizontally and verti-cally beneath into bull' thinly laminated or shaly limestone, weathering into slopes of marly clay. In these beds nodules of crystalline quartz with cal-cite and angular fragments of the same are common. Beneath the buff shales which constitute the bulk of the Kenwood beds lies a layer of green-ish or bluish fissile shale from a few inches to Jive feet thick. The upper limestones are usually involved. more or less in the Fayette breccia. The total thickness of the Kenwood beds is nearly forty feet. The basal blue shale in especial is lieliernd to represent the horizon of the Irnlependence shales. The latter term, originally designating some sixteen feet of dark car-bonaceous and grey fossiliferous shale pierced by a well near Independence, may readily be extended, however, to include all the limestone and shale of the Ken wooA. The latter term 1s, therefore, used only as a local synonym for the Independence shales, of which it offers many natural sections, the first discovered. Beneath the Kenwood beds in Linn county lies a Devonian terrane not hitherto known, termed the Otis beds. Like the Kenwood beds, from which it is somewhat sharply divided, the Otis linrcstone is remarkably constant and uniform in its lithological features, some layers with special character-istics being traced across the county. lt consists of nearly pure non-mag-nesian limestones, some macro-crystalline and some non-crystalline and compacted of impalpable calcareous silt, often heterogeneous in texture, often lying in hea\·y lenticular masses, pas.-;iug into thin calcareous plates. In all the !lumerous exposures of these beds from the Cedar ltirnr above and below Cedar Hapids to near the Jones county line southeast of Spring-ville, Spirifern Ec11imm/1owi (Hall) is found gregarious in a typical form dis-tinct from the varietal form found in the Independence shales at Inde-pendence. On the Buffalo and Wapsipinnicon rivers the numerous sections of the Otis limestone are uufossiliferous. The Otis beds, whose total thickness is thirty feet, include hard thinly-bedded magnesian limestone basal layers by which they pass without unconformity into softer heavily bedded dolomitic limPstones, probalily Si!Lirian in age, pro' isionally called the Coggan beds. It is believed that the Devonian sucecssion in Linn county will be found to obtain elsewhere iu the State where the lower strata of tlrn system are exposed. At Davenport, for example, the lower limestone out-cropping along the Mississippi rirnr from the city northward to Gilbertsville, thinly bedded, arched and partially brecciatecl, is identical in appearance with the frag· ments of the second stage of the Fayette breccia from Fayette to Cedar Hapids. Under the saddles of its folds there emerges a brown ferruginous limestone indistingui:ihahle from the Upper Kenwood, whose horizon it 2Proceedings of the Iowa Academy of Science, Vol. 1 [1893], No. 4, Art. 8https://scholarworks.uni.edu/pias/vol1/iss4/824 lOW A ACADEMY OF SCIENCES. seems to occupy. Lithologically and paleo11tologically the fossiliferous beds resting on these limestones at Davenport, referred by Barris to the Cornifer-ous, are believed to be equivalent to the Gypiclula occidentalis and Rhyncho-nella interrnedia limestone, whose presence defines the third stage of the breccia in Linn county, and which in Buchanan county has been named the Gyroce1tas beds. At Davenport, as in the counties to the northwest, the Gyroceras beds are succeeded by a soft, shaly limestone with a character-istic fauna. The writer has felt the need of delinite terms to designate these bed:s, and therefore suggests for the consideration of workers iu this ticld the name, Lower Davenport be(l8 for the lower unfussiliferous limestone at Davenport, the limestone which furnished the fragments for the second stage of the Fayette breccia. If a geographical as well a paleontological term should be found convenient for the fossiliferous limestone overlying these lower beds, the term Upper Davenport beds could be appropriately used as a synonym of the Gyroceras beds. The change in fauna is so distinct at the summit of the Gyroceras beds that it seems to the writer that they should be separated from the Cedar Valley limestones, as tlrn Independence shales have been. 1f the inferences we have drawn are correct, the "Upper Helderberg" of Hall, and the "Corniferous" of Barris, at Davenport, are superior to the horizon of the Independence shales. They must therefore be included in that broad biotic unity whose termini are the Independence shales and the Lime creek shales, whose fauna have been shown by Calvin to be so similar. It is an interesting fact that the new Devonian terrane, the Otis beds, found beneath the Independence shales, contains, as we have staled, as its characteristic fossil a Hamilton ancl Chemung species, and carries no species, so far as known, allied to pre-Hamilton faunas in other states. Geological Laboratory of Cornell College, December 28, 1893. CRETACEOUS FORMATIONS OF NORTIHVESTERN 10\V A. BY CHARLES R. KEYES. (Abstract.) Until recently little definite information has been accessible concerning the distribution and subdivisions of the Cretaceous deposits of Northwestern Iowa. Strata of Cretaceous age have been recognized from time to time at various poinis, but, as a rule, little detailed information has been recorded. As early as 1840 Nicollet called attention to certain sections near the mouth of the Sioux river which he regarded as Cretaceous in age. Since that time Cappellini, Marcou, Meek, Hayden, White and others have been through this region. In all these cases the rocks noted were in the imme-diate vicinity of the Missouri river. \Vhite gave more attention, perhaps, to 3Norton: Notes on the Lower Strata of the Devonian Series in IowaPublished by UNI ScholarWorks, 1893

Notes on the Lower Strata of the Devonian Series in Iowa

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Notes on the Lower Strata of the Devonian Series in Iowa

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