HISTORY OF BOYER VALLEY 499 



Missouri divide is lower than the minor divide a few miles to the 

 west and that the pattern of drainage on opposite sides of the Mis- 

 sissippi-Missouri divide is the same w'hile that on opposite sides of 

 the minor divide is different. He states his theory in the following 

 language: "In pre-Wisconsin time the Boyer river turned eastward 

 and passed through the Wall lake outlet toward Raccoon river. 

 When the ice-edge blocked this eastward drainage the ponded waters 

 in the valley broke over a low place in the great watershed near 

 Herring, in southwestern Levey township (Sac county), and es- 

 caped to Missouri river. This course was cut so low during ice- 

 occupancy, and the old valley to the east was so much filled that the 

 Boyer continued to flow to the southwest and did not again take its 

 eastward course to the Raccoon." 



Some of the objections to this theory have been set forth in prev- 

 ious paragraphs. The fact that the pattern of drainage on opposite 

 sides of the minor divide is different may be explained by the state- 

 ment that the Boyer is close to the crest of this divide and there is 

 little room for west-to-east tributaries to develop, while the Maple 

 flows, in a nearly parallel course, be it noted, several miles distant 

 Irom the crest, and therefore a well developed system of east-to- 

 west tributaries drains this western slope. 



The question arises as to why this overflow from the ice-ponded 

 waters should seek escape over the highest part of the bounding 

 rim rather than over some lower col. A study of the altitudes of 

 the region shows that in northwest Carroll county along the margin 

 of the Wisconsin moraine, the highest point reached by the railway 

 between Carroll and Wall Lake is 1,366 feet, at Breda. This is prac- 

 tically at the upland level. The railway between Wall Lake and 

 Odebolt crosses the high divide west of the Boyer at 1,378 feet. But 

 in northeast Crawford county, where the Boyer has cut its valley 

 through the ridge, the latter rises 1,500 feet or more above sea level 

 east of the river and over 1,400 feet between the Boyer and Otter 

 creek, while a little farther west, near Schleswig, the hills reach 

 altitudes well over 1,500 feet above sea level. There is no obvious 

 reason wdiy this high plateau, apparently the highest land south of 

 Alta, should be chosen as the locus of overflow for the glacial flood- 

 waters. On the other hand, however, if the southwestward flowing 

 post-Kansan Boyer be conceived of as extending its valley to the 

 northeast by headward erosion there is apparently no reason why 

 one of the vigorous members of its dendritic system should not 

 work its way up the slopes of the highlands and eventually cut 

 through what was once the real Mississippi-Missouri divide and so 



