496 IOWA ACADEMY OF SCIENCE Vol. XXVI, 1919 



in the thickness of the moraine. The sag just south of Wall lake 

 is filled with gravel to a height of thirty feet above the original floor 

 and similar gravel no doubt underlies the lake. The assemblage of 

 facts seems to indicate that while the ancient valley may have in- 

 cluded the sag, the western part of Wall lake and the wide part of 

 Indian creek near Lake View, it could hardly have included the 

 lower part of the creek to the east. 



If Raccoon river above the mouth of Indian creek once formed 

 part of the Boyer system we should' expect to find some differences 

 in the character of the valley above and below this point. The valley 

 above the creek mouth should show some evidence of being older 

 than the lower part. But the evidence does not point in this 

 direction. 



Opposite the mouth of Indian creek valley Raccoon valley is re- 

 markably wide, stretching nearly a mile from rim to rim. How- 

 ever, the actual flood plain is quite narrow, and is nowhere more 

 rhan two hundred or three hundred yards wide. The remainder 

 of the valley is occupied by a high second bottom or terrace which is 

 really a valley filling of gravel and clay from the Wisconsin glacier. 

 The old walls rise rather gently above this terrace and mark the 

 former limits of the valley. A very significant feature of the valley 

 filling is the fact that it extends from two miles above the mouth of 

 Indian creek at least two or three miles below that point. That is, 

 there is no change in the character of Raccoon valley near the mouth 

 of Indian creek. In fact all along its course below here the valley 

 shows evidences of its pre-Wisconsin age in its dimensions and its 

 form. 



Above the point already mentioned where the valley widens out 

 and is partly filled by Wisconsin drift materials the valley is narrow 

 and deep, steep bluffs flank the narrow flood plain and in its present 

 aspects the gorge presents the appearance of post-Wisconsin age. 

 Similar features are the rule in the valley from here to and beyond 

 Sac City and as far at least as the north county line. In a few 

 places, however, the valley shows what seem to be remnants of an 

 original pre-Wisconsin drainage course. One of the best of these 

 is in sections 25 of Delaware and 30 and 31 of Douglas townships, 

 where the valley flares out into a wide open bay about a long oxbow. 

 Another is just above Sac City, where the valley shows evidences 

 of filling, and other indications of the incomplete filling of an old 

 valley are not wanting. 



'Jlie conditions seem to point, then, to a pre-Wisconsin age for 

 Raccoon valley throughout its extent across Sac county. There can 



