6 Geology and Mineralogy of a part of Massachusetts, &c. 
ready referred to, and have supposed it to be connected 
with the gneiss of Middlefield. But I am not certain of 
the gneiss in that part of the section. 
3. MICA SLATE. . 
Colored Green. 
This rock constitutes the principal part of the rocks of 
the range along the eastern boundary of Berkshire. Un- 
der this name is included much that has generally been cal- 
led gneiss. The mica-slate, which appears along the mid- 
dle of Berkshire county, is the common variety, and read- 
ily distinguished. But farther east it is less slaty and the 
ingredients are mingled much more imperfectly. It has 
more of the appearance of layers, like gneiss. It is, how- 
ever, the mica-slate, described by Cleaveland and others, in 
which the “two ingredients alternate in distinct layers.” 
This is the reason that it has been often mistaken for 
gneiss. A careful examination, however, proves it to be 
destitute of feldspar. When I have attempted to melt it by 
the blow pipe, only mica has been found, showing its des- 
titution of one of the essential ingredients of gneiss. It 
seems very certain that. mica-slate is a far more abundant 
rock than has heretofore been supposed. Other geologists 
have lately expressed the same opinion of this rock. It 
lies on both sides of the gneiss, and much of it at a higher 
elevation. Indeed I am rather inclined to the opinion that 
the gneiss should be considered as beds in the mica-slate, 
than as one of the general strata. I have not, however 
examined with sufficient minuteness to state this to be the 
fact. 
The mica-slate appears under a variety of forms. The 
two most common are those already mentioned ; the one, 
the common slaty variety, and the other, in which the ingre- 
dients are in ‘“ distinct layers.’? Besides these, there are 
several others like those mentioned by Mr. Hitchcock, Am. 
Journ. Vol. VI. p. 23—4. It often splits into tabular 
masses, and sometimes has a very distinet grain, so that it 
may be split into most convenient forms for building stones. 
A ledge was shown me by Dr. E. Emmons at Chester, 
