327 



The rocks in the above section embrace all those which arc included 

 in the division marked C, in the Geological Section^ prefixed to this re- 

 port 



SANDSTONES IMMEDIATELY BELOW THE COAL. 



These sandstones, (marked D, in the plate,) as well as most of the for- 

 mations below the coal, were fully described in my report of last year. 

 I shall, therefore, now notice them only so far as to exhibit their relative 

 position in the series, viewed as a whole, and the extent of country oc- 

 cupied by them. 



These sandstones, which, in the report alluded to, are described under 

 the name of fossiliferous, fen-uginous sandstones, excepting in some of 

 the uppermost gtrata, are generally fine grained and of a yellow color. 

 Some strata of the latter abound in marine fossil shells, among which 

 the genus Nucula is very abundant, and there were observed species of 

 Atyrpa, Bellerophon, Euomphalis, and Pterinea. 



Though here classed as beneath the coal rocks, these sandstones are 

 associated with that series of rocks which are usually regarded as be- 

 longing to the carboniferous era. They occupy nearly the whole of 

 Calhoun county, the lower half of Jackson, and the northern half of 

 Hillsdale county ; through which counties their outcrops may be obser- 

 ved at numerous points, or they are reached in almost all the deep wells. 

 It is probable, also, that these rocks occupy most of the eastern portions 

 of Jackson and Shiawassee counties, east of the limestone stratum above 

 described ; and they make their appearance, at its eastern edge, on Lake 

 Huron, near the entrance of Saginaw Bay. 



The aggregate thickness of these sandstones may be estimated at up- 

 wards of 300 feet. 



CLAY, CONTAINING KIDNEY ORK OP mON. 



This very valuable formation immediately succeeds to the sandstones 

 above described, underlying them and cropping out at the extreme 

 southerly bend of the basin. It occupies a part of the south-western 

 portion of Calhoun county, the whole north-eastern portion of Branch 

 county, or nearly so, and part of the western and central portions of 

 Hillsdale. 



It consists of an indurated, grayish brown clay, having much the ap- 

 pearance of a shaly limestone or dark gypsum, regularly stratified, in 



