314 



C Upper coal and shales. 



r^ ri ^ I Lower coal and shale. 



U. Coal measures, s t i j i j <. 



I Included sandstones. 



Limestone stratum. 



D. Sub-carboniferous sandstones. 



E. Clay and kidney-ironstone formation. 



F. Sandstones, of Point aux Barques. 



G. Argillaceous slates and flags, of Lake Huron. 

 H. Soft, light colored sandstones. 



I. Black, aluminous slate. 

 K. Limerocks, of Lake Erie. 



These will now be considered, as nearly as may be, in their consecu- 

 tive order, beginning with the highest in the series. 



ERRATIC BLOCK GROUP, OR DILUVIAL DEPOSITS. 



These consist of sand, pebbles, and large water-worn masses of pre- 

 viously existing rocks, with occasional small, local beds of clay. They 

 have a thickness varying from one to upwards of one hundred feet ; 

 they form a universal mantle to the rocks, and constitute the soils of all 

 the interior counties. 



As this whole deposit is one of transport by water, and is made up of 

 the detritus and disruptured fragments of heterogeneous formations, its 

 character depends upon that of the rocks from which it is derived. For 

 instance, sand constitutes by far the greater proportion, and this circum- 

 stance may be, in part, accounted foi', from the fact of the immense 

 extent of sandstone rocks existing farther to the north ; and in part, by 

 the fact, further disclosed by the geological researches in the Peninsula, 

 that an immense thickness of rocks, mostly sandstone, which composed 

 the upper series of the coal measures, has been broken up and removed 

 from our geological series. Fine gravel constitutes the diluvium in the 

 next proportion, and is the result of a similar abrasion of rocks of 

 harder materials. Owing to the friable nature of the sandstones, as 

 might be expected, few lai-ge boulders of that material occur. Lime- 

 stone pebbles and boulders are abundant ; a condition which also might 

 be looked for, when we take into view the immense extent and thick- 

 ness of the limerocks of our State, they being by far the most promi- 

 nent formation above the primary. 



