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 
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 ; but 
they are, in general, too unimportant to need descrip- 
tion. Next to gneiss, it occupies more space than 
any of the other rocks of New-England. A great 
portion of Massachusetts is mica slate, and a broad 
