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SCIENCE 



[N. S. Vol. XXXIX. No. 999 



Platte, and compelling all the streams men- 

 tioned to find their way around the edge of 

 the ice southward, probably along the line 

 of the present Missouri, or a little west of 

 it, from Sioux City to Nebraska City and 

 quite likely for a time through the Grand 

 River of Missouri. 



We are assured that the ice entered east- 

 ern Nebraska and reached to the south line 

 of Iowa. In Dakota, it probably did not 

 enter the James River valley extensively, 

 for the gap by which it entered was prob- 

 ably narrow and its axis at right angles to 

 the lobe which filled the Red River and 

 Des Moines valleys. 



C. THE MISSOURI DURING THE KANSAN STAGE 



After a recession, we know not how far 

 back, the ice advanced again to its maxi- 

 mum extent. The ice filled the Des Moines 

 valley again, and overflowed southward to 

 central Missouri, westward to Lincoln, 

 Neb., and southwest to Topeka, Kan. As it 

 crowded the great stream which skirted its 

 edge, for the first time it overflowed the 

 divide separating it from the Kansas, at 

 "Weston, Mo., a little north of Leavenworth. 

 This fact is recorded in a stratum of boul- 

 ders, nearly 20 feet thick and extending for 

 miles along the bluffs east of the river. It 

 rests on Carboniferous shales which rise 

 about 140 feet above the present river. 

 Among the boulders are scattering ones of 

 northern origin attesting the vicinity of the 

 ice sheet. Of course, when the ice reached 

 Topeka, that locality of Weston was deeply 

 buried with ice, and the master stream was 

 forced much farther westward, as we shall 

 see. 



Meanwhile, the lobe entering the James 

 River valley found, no doubt, a freer access 

 because of the erosive work of the earlier 

 ice lobe and of the streams attending it, for 

 they worked on soft material. The latter 

 must have been quite large, for they 



drained the western edge of the ice quite 

 extensively. Besides, the head of the ice 

 behind was probably higher than before 

 and the push forward stronger. Moreover, 

 because of the latter condition, the ice over- 

 rode the divide to the north more, and the 

 push was more southward than before, so 

 that in this Kansan stage the Dakota ice 

 lobe reached perhaps as far south and west 

 as West Point, Neb., and became confluent 

 with the west edge of the Minnesota-Des 

 Moines lobe for hundreds of miles. 



As the ice advanced in the James River 

 valley the surrounding streams had to shift 

 laterally westward and when dammed rose 

 and overflowed local divides, working their 

 way southward around the ice. The Mis- 

 souri River entering the James River val- 

 ley from the north, probably with the 

 Souris, skirted the western edge of the ice, 

 through the Dakotas to the Niobrara, being 

 successively augmented by the various 

 streams before mentioned from the west. 

 Reaching the Niobrara it first followed it 

 eastward to the vicinity of Sioux City, but 

 later as the Dakota lobe crowded against 

 the highlands of northeastern Nebraska, 

 the river was choked off and, being dammed, 

 it formed a deep lake, reaching far north 

 along the western edge of the ice and 

 eventually overflowed southward from the 

 south bend of the Niobrara, past Creighton 

 and Plainview, where the channel is still 

 traceable, to the Elkhorn. 



So also farther south, the stream was 

 pushed westward by the advance of the 

 Kansan ice from the former course along 

 the east line of Nebraska, to a line along 

 Logan, Elkhorn and Platte rivers, and pos- 

 sibly for a short time over the divide into 

 the Nemaha to its earlier course through 

 Missouri. 



But eventually when the ice reached its 

 maximum, the stream from the Niobrara 

 before sketched crossed the line of the Elk- 



