STATE GEOLOGIST. 125- 



Alluvial and drift materials 92 ft. 



Brown sandstone, ( Woodville,) 19 ft. 



Shales, dark colored above, light below, 40 ft. 



Bituminous coal, : 3 or 4 ft. 



Highly arenaceous fire-clay and sandstones, 20 ft. 



Shales, below, dark, bituminous, 12 ft. 



Sandstone, with thin seams of coal, 10 ft. 



Shale, , 38 ft. 



White sandstone, (Parma,) 105 ft. 



The whole thickness of the coal measures here, between the 

 overlying and underlying sandstones, is thus shown to be 123 

 feet, which is the greatest thickness yet measured. Probably, 

 however, the thickness is still greater at Owosso. 

 ■ Putting all the observations together, (of which it is not nec- 

 essary to make any further details,) it appears that the rocks 

 of the coal measures occupy a shallew basin, th® longest axis 

 of which is nearly coincident with the axis of Saginaw bay. 

 This bay breaks over the northeastern rim of the basin, and 

 near its head the rocks will probably be found to exhibit their 

 greatest depression. It is not likely, however, that this depres- 

 sion varies greatly between Saginaw and Ionia county In 

 other words, the lowest depression of the carboniferous trough 

 lies beneath a line extending from Ionia county into Saginaw 

 bay. Along this line the coal measures will be found to have 

 the greatest thickness, and the coal seams will be developed in 

 greatest number and force. 



When we speak of the carboniferous basin or trough, it must 

 nevertheless be remembered that all these rocks repose very 

 nearly in horizontal^planes, so that the slight undulations into 

 which they have been thrown by gentle disturbances since their 

 solidification, have presented eminences and ridges which have 

 subsequently been more or less worn down. It follows, there- 

 fore, that the Woodville sandstone is hot everywhere found 1 

 covering the coal measures, even within the area that has been 

 described. The denudation has sometimes extended entirely 

 through this sandstone, or into the shales below, or even so far 

 as to reach below the coal seams. The tracts, however, within, 

 the carboniferous area, which have been entirely denuded of coal, 



