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 rese mbling 
diallage. I am not certain, this is the mineral, for I have 
not sufficient means of comparison. If it be diallage, e 
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 y a} Se Be Pe 
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 era colored, it strongly resembles 
certain varieties of mica-slat 
Associated with the iea-alite 3 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 
*It is very desirable that this name should be confined to the compart 
intended by Mr. Hi itchcock, While tale, steatite, or soapstone, need n 
° 
riat nded by 
Bakewell indeed; but his language is so indefinite, both in his definition 
of taleose slate, and in his remarks upon the substitution of tale for mica in 
some — eoology Ist Ed. p. 71 and 358,) that the fact is of little con- 
sequence, This t e slate is on Ceomy of talcose rock in the Index to 
the Gecloey of the aieere States, pages 34 and 147. But it is desirable 
to limit the term still more. This is done by confining it to a rock compo- 
sed of “talc and quartz.’’ 
