294 



stones. Ledges of this rock occur in the town of Somerset, section 

 seven, and Moscow, section twenty-nine, and are numerous through the 

 southern part of Jackson County. 



The included stratum. No. 4, (which is reached in general only in 

 wells,) owing to its superior hardness, serves admirably for the above 

 purpose. 



The whole thickness of the sandstones, below the lowest of the beds, 

 which embrace coal plants, will be found to exceed one hundred and 

 sixty feet. 



IV. TERTIARY AND DILUVIAL DEPOSITS. 



It has been already remarked, that in general, all the rocks are cov- 

 ered with a mantle of clays, fine detritus of the lime and sandrocks, or 

 loose water worn fragments of still older rocks, swept from the north 

 by the currents of a universal ocean, and deposited during the general 

 subsidence. 



Some evidences of the direction of these currents were noticed in 

 my Report of last year. Among these are the diluvial furrows and 

 scratches on the surface of the limerock, the appearance and direction of 

 which correspond with observations made in some of the more eastern 

 States. 



The extensive deposits of blue and yellow gravelly clays, which im- 

 mediately cover the limerock in Wayne aud Monroe Counties, were 

 found also to occupy the whole of the eastera slope of the Peninsula. 

 Except in the border Counties, these are overlaid by sand and gravel, 

 to a depth, probably, often exceeding one hundred feet. 



A corresponding clay was found bordering Lake Michigan, through 

 Berrien County, and is said to reach far out into the Lake at its south- 

 ern extremity. 



Pertaining to, or associated with these universal deposits, are beds 

 of clay, erratic masses of primary, transition and secc^ndaiy rocks, and 

 the more recent formations of marl, tufa, peat, and bog-iron ore. To 

 these I shall devote some separate practical consideiations. 



CLAYS. 



The extensive blue and yellow clays which next overlie the lirae- 

 TOck, are in general very gravelly, and contain also a large proportion 

 of carbonate of lime ; the blue in particular, effervescing strongly in 



