GNEISS. MICA SLATE. 227 



thus baffling all attempts at classification. The 

 gneiss region in some parts of New-England, as in 

 Worcester county (Massachusetts), furnishes an 

 excellent soil, owing to the sulphuret of iron con- 

 tained in the rock, which causes its rapid disinte- 

 gration. In this state, as a general rule, gneiss con- 

 tains but little iron, and is, consequently, very tough 

 and indestructible ; the soil, accordingly, where it 

 predominates, is thin and poor. Mr. Emmons re- 

 marks, " That in Montgomery, Herkimer, and Onei- 

 da counties, where the primary mass predominates, 

 we find one general character impressed on its sur- 

 face, that of having few inhabitants ; and so well 

 fixed are its limits, that it may in truth be said, that 

 population and that class of rocks are negatively 

 characteristic of each other. The connexion ex- 

 hibited in these counties of rock and soil, furnishes 

 another to the very many instances of the impor- 

 tance of geology to the causes of the difference in 

 the different parts of the earth as to agriculture 

 and its consequent population." 



Much of the primitive range already described 

 as extending south through the Atlantic States is 

 composed of gneiss. This rock forms a fine build- 

 ing stone, and it is very extensively quarried for 

 that purpose in the Easern States, under the name 

 I of granite. 



I Mica Slate. — This rock ranks next to gneiss in its 

 ! situation and age, and, indeed, is generally associa- 

 ! ted with it. Its essential ingredients are quartz 

 I and mica, but the mica predominates. Single speci- 

 mens may contain more quartz, but we must look 

 to the whole mass of the rock. There are ma»y 

 varieties of mica slate as well as of gneiss, Pro^ssor 

 Hitchcock having enumerated as many a» 14; but 

 they are, in general, too unimportant to P^ed descrip- 

 tion. Next to gneiss, it occupies m^re space than 

 any of the other rocks of New England. A great 

 portion of Massachusetts is roica slate, and a broad 



