PEBKUARy 20, 1914] 



SCIENCE 



271 



horn at Norfolk, went up Taylor Creek, 

 over the divide south at Creston, to the 

 Platte, and over the divide south of that, 

 near or east of David City, into the Big 

 Blue. From there the course is clear. 



The course from the Elkhorn to the Big 

 Blue is largely conjectural. There may 

 have been no distinct channel much of the 

 way, for any considerable time. Drift de- 

 posits in Nebraska seem more than usually 

 of a stratified or banded character espe- 

 cially toward the margin. There may have 

 been extensive shallow lakes over much of 

 the way. 



Some present altitudes along this course 

 will be instructive. Through the Dakotas, 

 the altitude may have been 1,600 to 1,700 

 feet; Plainview is 1,683, Norfolk, on the 

 Elkhorn, 1,525; Creston, 1,604; Schuyler on 

 the Platte, 1,350 ; David City, 1,607 ; Miller- 

 ton, on the Big Blue, 1,590. It may possi- 

 bly have reached the Big Blue by Skull 

 Creek and Oak Creek passing a little west 

 of Lincoln and over the divide near Berks, 

 without finding an altitude over 1,500 A. T, 



After reaching the Big Blue the course 

 was clear. The course was unobstructed to 

 the Kansas at Manhattan, Kan., and east- 

 ward by the latter stream around the ice to 

 the Mississippi. So at first, but as the ice 

 continued southward it for a time dammed 

 the Big Blue, a little below Blue Rapids, 

 Kan., forming a short-lived lake which cov- 

 ered the eastern half of Washington county, 

 Kan., and possibly at about the same time 

 formed a similar lake, Kaw Lake as it has 

 been called, in the valley of Kansas River, 

 by filling the trough of that stream with ice 

 from Wamego to Leeompton, a distance of 

 more than sixty miles. Kaw Lake, soon 

 fiUed and found an outlet over the divide 

 south 200 feet higher than the present 

 stream, and from the valley of one small 

 tributary of the Kansas to another, till 

 southeast of Topeka it reached the valley 



of the Wakarusa, which conveyed it around 

 to the valley of the Kansas below the barrier. 

 At Kansas City the ice sheet crowded 

 against the heavy limestone ledges in the 

 northern part of the city, while the river 

 occupied the valley in the southern part of 

 the city, which leads eastward to the Mis- 

 souri again. 



This course was occupied through Kansas 

 long enough to cut down quite a channel 

 and to pave it with boulders and gravel, 

 before the recession of the ice opened up 

 the channel of the Kansas again. 



D. WHILE THE KANSAN ICE WAS RECEDING 



Though the ice sheet of the Kansan stage 

 seems not to have paused in any one posi- 

 tion long enough to form a marginal mor- 

 aine anywhere, its advance and recession 

 must have been very slow. After the Kan- 

 sas resumed its preglacial course it cut 

 down considerably before it ceased to re- 

 ceive the drainage of the ice, or before main 

 drainage of the ice had shifted back to the 

 line of the present Missouri, south of 

 Dakota. 



Omitting many details that might be 

 given in the progress of shifting, I will 

 simply give one which has been studied. 



Wlien the Kansan ice was at its maxi- 

 mum, the master stream of drainage flowed 

 past Plainview at an altitude of 1,683. As 

 the ice receded to the east and north the 

 stream found a way at a lower level along 

 the edge of the ice for several miles and 

 then over the divide at Coleridge at 1,552, 

 and then down Logan Creek. This allowed 

 the rapid lowering of the water in the tem- 

 porary lake in the Niobrara, and caused 

 the deposition of much gravel along the 

 line. As the ice receded farther the stream 

 followed the ice front till it reached the 

 line of the former course of the Niobrara, 

 which passed northeast from its present 



