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 art 

 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 coimties of rock and soil, furnishes 

 another to the very many instances of the impor- 

 tance of geology to the causes of the difl'erence in 

 the different parts of the earth as to agricultuf^ 

 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 

 of granite. 



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 

 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 many 

 varieties of mica slate as well as of gneiss, Professor 

 Hitchcock having enumerated as many as 14 j but 

 they are, in general, too unimportant to need descrip- 

 tion. Next to gneiss, it occupies niore space than 

 any of the other rocks of New-England. A great 

 portion of Massachusetts is mica slate, and a broad 



