HISTORY OF BOYER VALLEY 497 



be no doubt of this age in its lower portions. If, therefore, Raccoon 

 valley is pre-Wisconsin in origin and its stream flowed to the Des 

 Moines then as now, where was the pre-Wisconsin course of the 

 upper Boyer? In view of the width of the valley of Indian creek- 

 opposite Wall lake, although it is just within the terminal moraine 

 where deposition would naturally be great, and in view also of the 

 narrowness of the valley farther east and of the character of Rac- 

 coon valley, it seems as if we must look for the northward continua- 

 tion of the ancient Boyer valley in this wide segment of Indian 

 creek valley and possibly in the narrower portion to the north- 

 west. Possibly, of course, the old valley above. this larger seg- 

 ment may have been entirely filled up and obliterated. 



It seems evident from the character of the modern upper Boyer 



valley that it has had a dififerent history than the valley in Crawford 



county, and it probably was only a branch which united with another 



which came from the northeast. Macbride indeed sketched such a 



history as this in one of his reports,^ but later in discussing Sac and 



Ida counties- he postulated an eastward flowing Boyer river whose 



headwaters were gathered from the ridge which stretches between 



Sclialler, Odebolt and Herring and now is cut through at the latter 



village. This theory seems to be based on the narrowness of the 



valley at Herring and Boyer, but it seems as though this narrowness 



may well be explained by the presence of the high ridge which would 



naturally require more work to excavate and hence might well be 



cleft by a valley narrower than that above ©r below. It may freely 



be admitted that the unoccupied valley in the vicinity of Wall Lake 



is abnormally wide but this may be accounted, for in part by the fact 



that several streams converged south of Wall lake, and in part by 



; the greater ease with which the river could widen its valley here 



b'.than in the much deeper and more steep-sided part between Herring 



^Sand Deloit. On the other hand it is hard to believe that a stream 



J«|, would normally make such a sharp turn as would be necessary for 



^;' the present upper Boyer if it had to flow eastward past Wall Lake 



^ to the Raccoon. 



Again it is only since the time of the last glacial invasion that 

 these drainage changes could have occurred and in view of the im- 

 maturity of much of the upper part of the Raccoon valley as sketched 

 above v/e should according to Macbride's theory expect similar im- 

 maturity in the Boyer at Herring. However, the valley here is 



'Geolog-y of Cherokee and Buena Vista counties: Iowa Geol. Surv., Vol. 



XII, pp. 330, 331, 337. . , ^ , c, -rr i v^t-t ,. con 



-Geolog-y of Sac and Ida counties: Iowa Geol. Surv., Vol. XVI, pp. 520, 



523, 524, 537. 

 33 



