BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA VOL. 33, PP. 491-514 SEPTEMBER 1, 1922 \ STAGES OF THE ICE AGE 1 BY WARREN UPHAM (Presented before the Society December 28, 1921) CONTENTS Page Sequence of glacial and interglacial stages....................................................... 491 Nebraskan' glaciation.................................................................................................. 493 The Aftonian interglacial stage............................................................................. 495 Kansan glaciation.... t............................................................................................. 499 The Yarmouth interglacial stage.......................................................................... 503 Illinoian glaciation..................................................................................................... 504 The Sangamon interglacial stage........................................................................... 505 Iowan glaciation and loess deposition................................................................. 506 The Peorian interglacial stage................................................................................ 506 Wisconsin glaciation.................................................................................................. 507 The Champlain stage................................................................................................. 510 Estimated time ratios................................................................................................ 512 S e q u e n c e o p G l a c i a l a n d I nterglacial S t a g e s Throughout the Glacial period of growth, culmination, and decline of the North American and European ice-sheets, the 'climate causing the snowfall and ice accumulation fluctuated to such an extent that the boundaries of the continental glaciation were alternately advanced and checked or drawn back. North America had five stages of widely extended icefields. First was the long time of Nebraskan glaciation, followed by a great recession of the ice-borders during an interglacial stage named Aftonian, from its stratified beds and fossils near Afton, in southwestern Iowa. The second and maximum extension of ice accumulation is named, in the Keewatin area of its outflow west of the Mississippi, the Kansan stage, which was broken by the Yarmouth interval of ice melting and retreat. With the Kansan glaciation, but in part spreading across the eastern edge of its 1 Manuscript received by the Secretary of the Society December 12, 1921. (491) Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/33/3/491/3414344/BUL33-0491.pdf by guest on 28 September 2021 492 W . XJPHAM---- STAGES OF THE ICE AGE drift sheet and melting later from the Mississippi, was the thirds or Illi- noian, icefield, belonging to the far extended Labradorian area of glacial outflow. After the Kansan and Illinoian stages, which appear to have been mainly contemporaneous, another retreat of the ice-sheet took place in the Sangamon interglacial stage. Both the Yarmouth and Sangamon areas of wavering glaciation, and the duration of their stages, were slight in comparison with the Aftonian stage, which was the most prolonged interruption of the Ice Age on this continent. Next were the Iowan and Wisconsin stages of glaciation, the fourth and fifth in the list of wide climatic fluctuations that successively amassed and melted back the North American icefields. The Iowan drift was followed by the chief deposit of the loess, a peculiar silt, which was weath­ ered and eroded in the vicinity of Peoria, in Illinois, previous to the re- advancing Wisconsin glaciation. Hence the name Peorian is applied to the interglacial time of recession of the ice-border between these stages of colder climate and ice-advance. Depression of the land during the Iowan glacial stage had given decreased slopes of the Missouri, Mississippi, and Ohio valleys, permitting them to receive the thick formation of the loess. The land subsidence appears to have remained, or even to have progressed for the northeastern part of our continent, during the Wisconsin stage, while the most prominent marginal moraines were amassed at times of pause or often some readvance that accompanied the general melting and final departure of the ice-sheet. After the ice had melted far back, the sea covered the depressed coast and reached inland along the Saint Lawrence, Ottawa, and Lake Cham­ plain valleys, forming fossiliferous marine beds, from which this latest and relatively short part of the Glacial period is named the Champlain stage. It is thus seen that the alternating Iowan, Peorian, Wisconsin, and Champlain stages, comprising the time of greatest subsidence of the continental glaciated area, were attended by the growth, fluctuations, and disappearance of the Iowan and Wisconsin icefields. These four late stages seem to have been somewhat closely continuous with the preceding Kansan and Illinoian maximum glaciation, which was widely separated from the Nebraskan stage by the Aftonian retreat of the ice boundaries. A similar sequence of glacial and interglacial stages has been traced in the British Isles, northern Europe, and the Alps, which indicates that the climatic conditions producing the Ice Age on the continental areas at opposite sides of the Atlantic were approximately contemporaneous, and that their fluctuations of glaciation were caused by like secular changes of climate. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/33/3/491/3414344/BUL33-0491.pdf by guest on 28 September 2021 GLACIATION IN NEBRASKA 4 9 3 N e b r a s k a n G l a c i a t i o n The earliest recognized stage of great extension of the ice-sheet upon Canada.and the United States has been named Albertan and Jerseyan, from its drift in Alberta and New Jersey. Following a suggestion of the late Prof. Samuel Calvin, the preferable name Nebraskan was proposed by Prof. B. Shimek2 for this stage. Thus all the series of North Amer­ ican ice advances and recessions, if the Champlain stage be excepted, are named from the glacial drift and alternating interglacial beds within the drainage basin of the Mississippi. Eroded river valleys have occasional exposures of Nebraskan drift, beneath the Kansan drift and formations of Aftonian age, in eastern Nebraska and in southern and eastern Iowa; but its most western and southern extension in that region was probably everywhere overspread and surpassed by the Kansan icefield. East of the Mississippi the early Patrician transportation of copper fragments and drift boulders from the region of Lake Superior to central and southern Ohio seems referable to the Nebraskan stage of glaciation. Belonging originally to Patrician drift, but later carried onward as a part of the Illinoian drift, Prof. G. F. Wright found boulders of red jasper conglomerate near Cincinnati, borne beyond the Ohio River into the north edge of Kentucky, where they were deposited at the extreme boundary of the ice-sheet after a southward glacial journey of about 500 miles from their parent ledges, east of Lake Superior and north of Lake Huron. In northeastern Pennsylvania and northern New Jersey the attenuated border of the drift, extending 10 to 25 miles south of the terminal mo­ raine, is referred by Chamberlin and Salisbury to the first great stage of our continental glaciation, named by them Jerseyan, probably correlative with the Nebraskan stage and the ancient Patrician drift. It is remark­ ably contrasted with the adjoining drift sheet of Wisconsin age, which includes the thick moraine and spreads thence far north upon New York, New England, and eastern Canada. The thin Jerseyan drift remains in patches, and indeed it may have been originally so deposited. Formed mainly by the local snowfall, the thin border of the early icefield probably had low surface slopes, without sufficient movement in many portions for drift erosion, transportation, and deposition. Reaching more than 1,200 miles from the Missouri River to the At­ lantic close south of New York City, the southern margin of the most ancient known stage of our continental glaciation fell not very far short of the later maximum icefield in Kansas and Missouri. It attained nearly 2 Bulletin Geol. Soc. of America, vol. 20, December 24, 1909, p. 408 ; also in Science, January 14, 1910. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/33/3/491/3414344/BUL33-0491.pdf by guest on 28 September 2021 4 9 4 W . U P H A M ---- STAGES OP THE ICE AGE the same lim it as the Illinoian and Ohio drift, which was early borne southward from the Patrician central area of outflow, but later from the more eastern Labradorian area. On the southwest edge of the very broad Quebec lobe of that eastern icefield, from the reentrant angle of the glacial boundary near the east end of Lake Erie to the coast of New Jersey, the earliest drift extends beyond the latest Wisconsin glaciation, which is bordered by a belt of prominent morainic ridges and hills. 'With so great southward extension of the ice-sheet in the- Nebraskan stage on the east half of our continent, it doubtless covered nearly all of Minnesota and the upper part of the Mississippi basin, excepting the large driftless area, mostly in Wisconsin, which was exempt from glacia­ tion through all the Ice Age. Across the Canadian provinces of Saskatchewan, Alberta, and British Columbia, and over the adjoining border of the United States, the Kee- watin and