PRELIMINARY CHAPTEK. 5 



day: piecc of float mineral are found, sometimes in con- 

 siderable quantities, and before the solid strata are found, 

 apparently lying /// #//M. unworn by water, and becoming 

 more numerous, until the solid rock is reached, as if they 

 v.ere harder fragments of the original rocks, which have 

 withstood the general decay of the ma--. 



Fragmentary patches of the lead region are undoubtedly 

 drift less regions, but in many places the drift has invaded 

 the lead regions. In the north-western portions of Carroll 

 county, where the indications are strong that the soils and 

 clay are derived from the decomposition of the Underlying 

 rocks, fragmentary boulders are often found on the surface 

 of the ground and in the ravines, showing, as it seems, that 

 even the>c driftless lead regions have been submerged, per- 

 haps many times, since their uplift from the Silurian seas. 



The finely comminuted, greenish and creamy yellow col- 

 ored clays, forming the sub>oil over small extents of Xorth- 

 western Illinois underlaid by the Cincinnati shales, would 

 >eem to indicate an origin from the decomposition of the 

 earthy shales below. 



But in many places and over large extents of this part of 

 the State, the transportation of soils and clays, and a uni- 

 versal mingling and mixing of the surface materials of the 

 earth, is a fact patent to the most casual oliserver. The 

 gravel hills of Ogle county, and the long gravel beds of 

 AVinnehago and Boone counties, mingled with white sand; 

 the stratified and partially stratified clays and sands to be 

 met with almost everywhere: the boulders scattered over 

 the prairies all owe their present arrangement to the drift 

 forces. Over these places the underlying rocks are hidden 

 by the concealing drift. Laminated clays cover the indu- 

 rated ro.-k-. The>e days are in some ca<e> nothing but the 

 M -diluents and precipitates of peaceful, shallow seas: but 

 the boulders and gravel beds indicate mightier forces and 

 belong to the true glacial drift. That vast glaciers of ice 

 once extended over large portions of Xorth America is now 



