104 IOWA ACADEMY OP SCIENCES. 



the relation that the two latter have to each other can not be 

 fully made out from the known exposures. In the well on 

 Thirty-fifth street in Rock Island there seemed indeed to be 

 two soil horizons. The section under the Kansan till was as 

 follows, beginning above: 



FEET. 



Black sticky muck with large fragments of wood . . 4 

 Loess-like, ash-colored material with pulmonate 



fossils 8 



Black muck 4 



Residual clay full of local rock fragments 5 



Coal measures 



All the fragments of wood found in the ancient soils belong 

 to gymnosperms, and this may .be regarded as indicating a 

 boreal climate, such as would precede the advance of the ice. 

 The position of the deposits under the till indicate that they 

 are pre-Kansan in age, and possibly preglacial. The region 

 in which they occur lies to the south of the Driftless area, 

 where the abrasive work of the ice seems to have been 

 small in amount. Erosion contours of two and three hundred 

 feet in elevation lie buried under the drift in this region, and 

 glacial scorings are unknown. Among such surroundings it 

 would be more singular that preglacial surface deposits should 

 be wholly absent than that they should occasionally come into 

 view. 



