Schiston Rocks. 



11 



etable matter ; and this limestone is common in Berkshire County. 

 But it occurs there in beds, alternating with the pure carbonate of 

 lime, and I apprehend rarely produces any bad effect. 



Quartz Rock. 



It will be seen by the map that one variety of this rock is associ- 

 ated with mica slate, and another with gneiss ; so intimately, indeed, 

 that its agricultural character may be considered the same as that of 

 these rocks. When it occurs in the state of pure quartz, it is so lit- 

 tle acted upon by the common decomposing agents, such as air, heat 

 and moisture, as to exert little or no influence upon the superincum- 

 bent soil ; except in the town of Cheshire, where it produces a pure 

 white sand. 



Chlorite Slate, Talcose Slate, Mica Slate. 



The first of these rocks occupies too little space to deserve any no- 

 tice in respect to the soil resulting from it. The second is in general 

 a mere variety of mica slate, talc taking the place of mica, or being 

 superadded to it. Where the talcose slate, however, is most pure, so 

 as in fact to be little else but slaty talc, with more or less quartz, the 

 soil which its decomposition produces, is decidedly inferior to that re- 

 sulting from mica slate ; and probably this is owing to the large quan- 

 tity of magnesia which talc contains. 



Mica slate produces a soil of a medium quality. Some varieties of 

 it underlie tracts of superior quality. But the most extensive tract of 

 mica slate in Massachusetts, consists of the high and mountainous re- 

 gion west of Connecticut river : so that it is difficult to compare the 

 soil lying over it, with that of formations at a lower level. The deep 

 ravines, however, so common in the mica slate, furnish many very 

 fertile, though limited patches of ground ; while the mountain sides 

 are very superior for grazing. 



Hornblende Slate, Gneiss, 



Gneiss, which differs from granite only in having a slaty structure, 

 occupies more of the surface of the State than any other rock. It 

 sometimes takes into its composition the black mineral called horn- 

 blende ; even losing its common ingredients : and then it is denomin- 

 ated Hornblende Slate. 



The soil resulting from the decomposition of gneiss is so well mark- 

 ed, as not to be easily mistaken by an experienced eye. Its predomi- 



