298 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



deposit. In some cases they may have been brought up from the underlying 

 till by burrowing animals long after the silt was laid down; but in other 

 cases they seem to have been brought in during the process of deposition. 

 A few were found in the unglaciated parts of southeastern Ohio, where their 

 presence seems difficult to explain unless they were laid down with the silt. 

 The pebbles are generally of quartz, though a few other very resistant 

 rocks are represented ; this is true of pebbles in both the glaciated and the 

 unglaciated tracts. 



Chemical constitution. — But ouc aualysis of this silt has been reported. This 

 first appeared in the Greology of Ohio,^ and was made by T. G. Wormley, 

 State chemist. The specimen was obtained on the level upland in western 

 Highland County. 



Analysis of white clay from western Highland County, Ohio. 



Per cent. 



Water combined 5.54 



Silicic acid ' 62.60 



Alumina 18.90 



Sesquioxide of iron 6.30 



Manganese 0.20 



Phosphate of lime 0.63 



Carbonate of lime 1.89 



Carbonate of magnesia 1.82 



Potash and Soda 2.32 



Total • 100.10 



Mineraiogicai constitution. — Two saiuplcs coUectcd by the writer have been 

 examined microscopically by R. D. Salisbury. One is from Beech Flats, 

 in northwestern Pike County, Ohio; the other is from western Highland 

 County, not far from the locality from which the sample subjected to 

 chemical analysis was obtained. One is very near the glacial boundary, 

 the other 15 or 20 miles back froin the boundary. No essential difference 

 was found in the samples. Both consist mainly of quartz grains, among 

 which are feldspar fragments, hornblende, and possibly epidote and augite ; 

 there are also coarse grains of chert and minute concretions of iron oxide. 

 The matei'ial is largely angular, even when the grains are of sufficient 

 coarseness to have been liable to become rounded under favorable conditions. 



PROBABIiE low AN AGE. 



Standing, as it does, above the Sangamon weathered zone and below the 

 Wisconsin drift, the position of the silt is similar to that of the lowan drift. 



' Vol. I, p. 445. 



