22 SUB-HIMALAYAN ROCKS OF N. W. INDIA. [CHAP. II. 



Before going any farther, I must anticipate any ambiguity that 



might arise from the uncertain meaning of some 

 Rock-terms used. 



common rock names. The word " slate" is far 



too familiar and appropriate to be limited only to rocks exhibiting 



in some perfection the special phenomenon of cleavage. It is now 



often denned in this sense, but such is not its general use among English 



writers. Such a restricted definition would be an awkward impediment 



in describing these hills where cleaved rocks are not common, though 



there is abundance of indurated argillaceous rocks to which the words 



slate and slaty in their common acceptation are 

 Slate and grit. 



peculiarly applicable. As a correlative word to 



slate, I use th'e word ' grit' to indicate a large intermediate class of rocks, 

 too fine grained and earthy to be called sandstone, and too rough for a 

 slate. Of all sedimentary materials in their unaltered state it is only 

 the very fine silts that become indurated into slates; most clays, 

 earths, and muds would by induration result in grits. In adopting 

 this meaning for the word grit, I am again accepting the practice of 

 English field geologists, so far as my experience goes. The usual 

 glossary-meaning of the word is a sharp sandstone, coarse or fine ; but 

 for the purposes of descriptive geology this definition is almost useless. 

 There is even a direct objection to such an application of the term ; 

 why remove a simple variety, as sufficiently indicated by the term 

 ' sharp,' from under the generic name sandstone ? We cannot do with- 

 out a class name for the rocks I designate grits. I only apply the word 

 1 schist' to foliated rocks, — rocks in which sub- 

 crystalline metamorphism is distinctly seen. Of 

 course the varieties produced by gradations are endless ; but I wish 

 to convey the idea that these terms are only used to designate each 

 a class of rocks. In using compound names to express interme- 

 diate varieties, the noun, or the last word of a compound name is 

 that whose characters preponderate ; as e. g. quartzite-sandstone, to 



