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on 03 October 2021 by guest Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/23/1/463/3413333/BUL23-0463.pdf BULL. GEOL. SOC. AM. VOL. 23, 1911, PL. 25 MAP OF PRE-WISCONSIN CHANNELS IN SOUTHEASTERN SOUTH DAKOTA AND NORTHEASTERN NEBRASKA BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA V o l . 23, PP. 463-470, PLS. 25-27 SEPTEMBER 26, 1912 PRE-WISCONSIN CHANNELS IN SOUTHEASTERN SOUTH DAKOTA AND NORTHEASTERN NEBRASKA 1 BY J. E. TODD (Presented before the Society December 28, 1911) CONTENTS l 'n g o General relations.................................................... 463 Channels of the earlier stage....................... 464 The Creighton-Plainview channel............ 464 The Hartington-Coleridge channel............ 464 Channels of the later stage.............................. 466 General conditions........................................ 466 The ancient Niobrara.................................. 466 The ancient Ponca........................................ 467 The ancient Mosquito.................................. 468 The ancient Choteau.................................... 469 Conclusions.............................................................. 470 GrENEJiAL RELATIONS Nearly 30 years ago it was discovered that in the early Pleistocene the master stream of the southeastern South Dakota region followed the valley of .lames River to its present mouth and then the Missouri below, and also that the present course of the Missouri above Yankton was out­ lined around the edge of the great ice-sheet as late as the Wisconsin stage. Later studies made in preparing the Elk Point folio led the writer to the conclusion that there had been an earlier advance of the ice-sheet down the James River Valley at a time when the drainage level was about 300 feet higher than at present. Whether this was during the Kansan stage or the Iowan stage has not been determined, but probably it was during the Kansan. At that stage the Dakota lobe extended as far south as West Point, Nebraska, and the drainage from the west side 1 Manuscript received by the Secretary of the Society January 10, 1012. (463) Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/23/1/463/3413333/BUL23-0463.pdf by guest on 03 October 2021 4 6 4 J . E. TODD----PKE-WISCONSIN CHANNELS IN DAKOTA-NEBRASKA of the ice and of the country west flowed south through a channel pass­ ing near Creighton and Plainview into north fork of Elkhorn River. This old channel is now at an altitude of about 1,700 feet. As the ice receded the main drainage outlet shifted eastward to a lower valley which passes near Hartington and Coleridge and connects with the valley of Logan Creek. This channel now has an altitude near 1,600 feet. Still later the drainage flowed along the present course of the Missouri, where the altitude is 1,200 feet. During the following interglacial epoch the channels about Elk Point were deepened about 100 feet—that is, nearly to their present level. At that time the valley of the Missouri River above Yankton was not in existence, and the Nio­ brara crossed the line of the present Missouri Valley east of Springfield, South Dakota, and entered the James River Valley a few miles north of Yankton. Ponca Creek also crossed the Missouri Valley and after a northward bend joined the old Niobrara near Springfield. A stream of similar size came past Port Randall—whether from Pease Creek or Lake Andes has not been ascertained—passed several miles north of Green­ wood, South Dakota, crossed Choteau Creek near its mouth, and joined Ponca Creek a few miles farther east. The following facts are the evidence on which the above statements are based. The events are considered in chronologic order: C h a n n e l s o p t h e E a r l i e r S t a g e THE CREIGHTON-PLAINVIEW CHANNEL The principal evidences indicating that an ancient stream flowed past Creighton are the existence of a shallow valley connecting the upper portion of Verdigre and Bazile creeks with the upper portion of the north branch of the Elkhorn and the relations of this valley to the earlier drift. It is about a mile wide and ¡30 or 40 feet deep near Plain- view, where it is least affected by erosion. It lies between the till- covered area to the northeast and the area of Tertiary sands- to the southwest, on which there is but little drift. Traces of the channel northward have been obliterated by the erosion of present streams and by the effects of the Wisconsin ice. THE HARTINGTON-COLE RIDGE CHANNEL That a stream flowed past Hartington and Coleridge is clearly indi­ cated by the extensive gravel deposits shown on the map, plate 25. This gravel is first prominent a few miles east of Niobrara, Nebraska, 415 to 450 feet above the Missouri, and extending eastward across, Bazile Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/23/1/463/3413333/BUL23-0463.pdf by guest on 03 October 2021 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/23/1/463/3413333/BUL23-0463.pdf by guest on 03 October 2021 BULL. GEOL. SOC. AM. VOL. 23, 1911, PL. 26 Figure 1.—Eroded gravel Stratum in Bottom of ancient Channel Looking east from point E on the map Figure 2.— Gravel over volcanic ash. Stratum Four miles south of Santee. Nebraska, looking west-southwest from point D. The shoulder marks the gravel stratum and the white spots in the road the volcanic ash Figure 3.—View east-northeast across the Hartington-Coleridge Valley PRE-WISCONSIN CHANNELS IN NORTHEASTERN NEBRASKA Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/23/1/463/3413333/BUL23-0463.pdf by guest on 03 October 2021 CHANNELS OF THE EARLIER STAGE 4 6 5 Creek to Weigand Creek. It forms a distinct terrace in places and there are also numerous gravel-topped knobs. South of Herrick a portion of it has either been let down by the undermining of the Tertiary sands below or been rearranged at a lower stage of the stream. Some years ago2 I regarded these gravels as remnants of a high ter­ race of the Missouri and not part of the Coleridge channel, an interpre­ tation based on a record of elevation at Coleridge which was given 100 feet too high. Later when the gravel was traced past Hartington its relations were made clear. In places where the deposit has been cut through by later drainage the gravel remains as a cap on adjacent bluffs and knobs somewhat resembling moraines,3 and they were so regarded by Aughey.4 A view of such is given in figure 1, plate 26. South of Santee agency the gravel is underlain by a stratum of vol­ canic ash several feet thick, which lies on laminated clay containing fresh-water shells.5 This ash is shown in figure 2, plate 26, from a photograph taken at D on the map, plate 25. At Coleridge, where the Coleridge-Hartington channel passes through the divide at an altitude of 1,550 feet, it is represented by a valley 3 to 4 miles wide, with its floor about 150 feet below the adjoining loess plain. This wide valley includes two or three subordinate channels or intervales 20 to 30 feet deep, with broad, flat ridges intervening which may have been bars or islands in the ancient streams. A view across the valley at Coleridge is given in figure 3, plate 26. Some features of these old channel gravels suggest that they may have had a similar history to that of the Aftonian gravels, lately described by Professor Shimek,6 as exten­ sively developed in western Iowa. No correlation can be offered, but the difference in altitude appears to show that they are not contemporaneous. It is likely that at the time of deposition of the gravels in the Coleridge- Hartington channel the drainage to the south was farther west than .the present Missouri River, and probably passed into a lake or series of lakes in eastern Nebraska which may transiently have drained southward into Big Blue River.7 It seems not impossible that both formations are to be connected with the Kansan ice-sheet, and that the thin deposit of till, which is found overlying the Aftonian in places, may belong to the 2 Bull. U. S. Geol. Survey, No. 158. 3 See also U. S. Geol. Survey, Geol. Atlas IT. S., Elk Point folio, No. 156, p. 5. * Physical Geography and Geology of Nebraska, p. 256. 6 Bull. U. S. Geol. Survey, No. 158, p. 70. 6 Iowa Geol. Survey Reports, vol. 20, and Bull. Geol. Soc. America, vol. 21, p. 81, 7 See Trans,. Kansas Acad. Sci., vol. 22, p. 107, Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/23/1/463/3413333/BUL23-0463.pdf by guest on 03 October 2021 4 6 6 J . E. TODD---- PRE-WISCONSIN CHANNELS IN DAKOTA-NEBRASKA Iowan stage, the occurrence of which is so problematical, especially in western Iowa. C h a n n e l s o p tt iid l a t e r S t a g e GENERAL CONDITIONS As already stated, the other channels considered belong to the. drain­ age of a later epoch when the conditions were considerably changed. The Kansan ice had disappeared and the larger streams were running much as before its advent. For convenience these channels are named after present streams which occupy portions of the old channels. They will be described in the order of their size, namely, the Niobrara, Ponca, Mosquito, and Choteau. THE 'ANCIENT NIOBRARA There will here be considered only the old course from Niobrara, Ne­ braska, to the James. Presumably its former course elsewhere was the same as that of the present stream.

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