12 Geology and Mineralogy of a part of Massachusetts, &c. 
Diallage Rock? Jameson. 
In the mica-slate at Chester, Dr. Emmons has found a 
rock, not extensive, which contains a mineral resembling 
diallage. I am not certain, this is the mineral, for I have 
not sufficient means of comparison. If it be diallage, the 
aggregate is diallage rock. I mention it for investigation. 
It is highly probable too that among the aggregates, of 
which augite forms an ingredient, Dr. MacCulloch would 
find augite rock. 
Connected with mica-slate is 
TALCOSE SLATE. 
Colored yellow and dotted. 
A stratum of this rock, composed of tale and quartz, is 
given by Mr. Hitchcock, Vol. VI. page 26 of this Journal. 
As it comes just within the limits of my map I have laid it 
down, not without strong suspicion that, at least from Plain- 
field southwards, it is merely mica-slate of a finer and sof- 
ter texture. Though lighter colored, it strongly resembles 
certain varieties of mica-slate. 
Associated with the mica-slate in the western part of the 
county of Berkshire, is 
Talco-micaceous Slate. 
By this name is intended that kind of mica-slate which 
contains a small quantity of talc. The talc is sometimes a 
mere ‘‘glazing,” as is remarked in the Geology of the 
Northern States, page 147. This rock is a variety of the 
talcose rock of the Geology just mentioned ; but it differs 
* It is very desirable that this name should be confined to the compound 
intended by Mr. Hitchcock. While talc, steatite, or soapstone, need no 
other name for geological purposes, this compound deserves one. Talcose 
slate is descriptive and appropriate. It may not be the rock intended by 
Bakewell indeed; but his language is so indefinite, both in his definition 
of talcose slate, and i in his remarks upon the substitution of tale for mica in 
some rocks, (Geology, Ist Ed. p. 71 and 358,) that the fact is of little con- 
sequence. This talcose slate is one variety of talcose rock in the Index to 
the Geology of the Northern States, pages 34 and 147. But it is desirable 
to limit the term still more. This is done by confining it toa rock compo- 
sed of “talc and quartz.’’ 
