February 20, 1914] 



SCIENCE 



273 



posits, moraines and till, show that the ice 

 pushed westward up each of the valleys 

 nearly to the line of the present Missouri. 

 In other words, the ice filled the present 

 James Eiver valley so completely that all 

 the western streams were dammed and the 

 waters rose in each till an outlet was found 

 southward. Between the Missouri and 

 Cannon Ball and Grand rivers the divides 

 were low and of soft material. But be- 

 tween the Grand and the Cheyenne was a 

 prominent ridge capped with Fox Hills 

 sandstone rising over 2,000 A. T. North of 

 this was formed Lake Arikaree, reaching 

 lip the line of the present line of the Mis- 

 souri to or beyond the mouth of the Yellow- 

 stone. Into it at several points the ice 

 sheet at its maximum dropped small ice- 

 bergs, by which boulders were scattered 

 over the bed of the lake, and particularly 

 on its southern margin, which is now in 

 places marked by a line of boulder-capped 

 buttes and ridges apparently correspond- 

 ing to an old water level or lake margin. 



The divide between the Cheyenne and 

 White rivers was again comparatively low, 

 but that between White and the Niobrara 

 was again high, nearly 2,000 feet A. T., 

 and capped with Tertiary sandstone. 

 Through this an outlet was started which 

 now is an imposing gorge, 750 feet deep. 

 The ice also blocked the Niobrara from 

 Springfield to Yankton, but did not force it 

 over the divide southward as during the 

 Kansan stage. Instead the river was 

 crowded up on the south side of its valley 

 where it excavated so deep a channel before 

 the retirement of the ice that it became 

 permanent. 



So we have the present course of the 

 Missouri from Ft. Stevenson to Yankton as 

 a direct result of the Wisconsin stage of 

 the ice sheet, as the course from Sioux City 

 to Nebraska City was probably determined 

 by the Nebraskan stage and from Nebraska 



City to Kansas City and possibly to its 

 mouth by the Kansan stage. 



G. DURING THE RECESSION OF THE WISCONSIN 

 STAGE 



The Wisconsin was the last great in- 

 vasion of the ice sheet, and its recession was 

 long and marked by long pauses, when 

 belts of knobs and ridges of debris were 

 dropped from the nearly stationary edge 

 of the ice. The first of these and the most 

 voluminous was formed a few miles within 

 the maximum extent of the ice. Before the 

 next was formed there was recession far 

 within the line of the second moraine and 

 then an advance and a pause to form the 

 second moraine. So that the Wisconsin 

 stage had many substages similar to the 

 stages already reviewed except that they 

 were shorter and with ever-waning extent. 

 During the recession from the first moraine 

 there was the unloosing of great volumes of 

 water as there was at the close of the Kan- 

 san, laden with much sediment, coarse and 

 fine. The coarse dropped near the edge of 

 the ice-formed valley trains, the fine, car- 

 I'ied far, formed a deep accumulation of 

 silt, particularly in broader and stiller 

 portions of the streams. Such deep de- 

 posits are found well-preserved at many 

 points. Their upper surface seems origi- 

 nally to have been nearly flat like a river 

 terrace, but is now not only deeply eroded, 

 but is more or less increased in height by 

 the wash from the upland back. The lower 

 limit is of course uneven, but usually is 

 only a few feet above the present level of the 

 streams. This deep silt and sand deposit is 

 frequently from 80 to 120 feet deep. It 

 closely resembles the loess often found on 

 the uplands in the vicinity. In fact they 

 have often been confused, nor is it any 

 wonder. 



This lower loess or early Wisconsin flood 

 deposit is finely exposed at Kansas City, 



