1(1)2 IOWA ACADEMY OF SCIENCES. 



SOME PREGLACIAL SOILS. 



BY J. A. UDDEN. 



In the region south of the Wisconsin Driftless area an old 

 soil is occasionally found under the Kansan drift, generally 

 resting on the bed rock, and often associated with laminated 

 water-bedded clay and other silt. It is exposed under a bluff 

 of drift in the southern part of Muscatine, Iowa. The material 

 is here dark brown in color, mottled with small black fragments 

 of vegetable tissue. The upper part is a dark mucky clay. 

 The whole bed is only two or three inches in thickness. It lies 

 below what appears to be pre- Kansan drift. At Davenport, 

 Iowa, a similar bed was uncovered in the grading of the river 

 bluff on the east side of Eastern avenue. At this place it had 

 a somewhat darker appearance, owing possibly to the fact that 

 it had been less subject to recent leaching in the exposure 

 made. At Rock Island, 111., the same soil bed has been 

 encountered in several wells which have been dug near the 

 river bluff. One of these wells is near the crossing of Thirty- 

 fifth street and Seventh avenue. The section penetrated by 

 this well consisted of loess, apparently two sheets of till, silt, 

 varying from a black muck to a grayish loess with small 

 gasteropods, and then a greenish sticky clay containing frag- 

 ments of the local bed-rock but apparently no archaean pebbles 

 or bowlders. This latter clay was some five feet in thickness 

 and rested on the soft shales, or clays, of the coal measures. 

 It seemed to be a residual material of preglacical age, lying 

 undisturbed on a slope of the bed-rock. The silt and muck 

 above it contained fragments of wood, one of which measured 

 nearly two feet in length and several inches across. Silt of the 

 same kind and in the same position, but oxidized and without 

 fragments of wood, has been exposed in the grading of some of 

 the streets near by. On Thirty-ninth street it contained the 

 following fossils: 



