322 



twenty feet. Both, clays contain at least twenty per cent, by weight, of 

 carbonate of lime, and this marly character injures them materially for 

 the manfacture of bricks or potteiy. 



On the western slope of the Peninsula, the place of the yellow and 

 blue clays is sometimes supplied by clay of a reddish color, of great 

 thickness. No fossils have yet been discovered in any of the clays of 

 this formation. 



COAL MEASURES. 



The rocks which include the coal beds of our State, occupy, com- 

 parati\ely but a small portion of that part of the State under conside- 

 ration, and are embraced within the counties of Jackson, Calhoun, Ing- 

 ham, Eaton, Kent, Ionia, Clinton, Shiawassee and Genesee. They con- 

 sist of strata of sandstone, shale, coal and limestone. Covered as these 

 rocks are, with thick deposits of diluviums and clays, they make out- 

 crops at but few points, and the determination of their order and extent 

 has been a matter of no small difficulty. From the dip of the rocks 

 composing these measures, there can be little doubt that the coal basin 

 extends northerly beyond the counties named, perhaps as far as to the 

 head branches of the Tittabawassee and Maskego rivei-s. But that 

 country is, as yet, almost wholly unsettled; and though partial explo- 

 rations have been made through it, since the commencement of the geo- 

 logical surveys, the thick mass of overlying materials has hitherto pre- 

 vented a determination of the northerly extent of these rocks. 



LIMESTONE STRATUM. 



As this stratum, from its position, (being the lowest in the series,) 

 determines the extent of the rocks, consideied as composing our coal 

 basin, I shall, for the sake of greater precision, give to it the first con- 

 sideration. 



A gray limestone, in irregular, detached beds, is found along the ex- 

 treme border of the coal-bearing sandstones. They are evidently re- 

 lics, in place, of a thin but extensive stratum, and as no coal has been 

 found below this rock, I have assumed it as the terminating rock of the 

 "coal measures" proper of our State. Following this rock, as it 

 makes its occasional appearance, the southerly limits of the coal basin 

 may be traced by a line, drawn from the Shiawassee river, at Corunna, 

 through the easterly pari of Ingham and Jackson, between ranges one 



