260 =o od. zD. Dana— Geology of Vermont and Berkshire. 
era had nearly or quite passed, we leaniicthiat all the various 
mica and chloritic schists mentioned, and the varieties of 
gneiss, and ‘a6; the other rocks designated, as protogine, gran- 
ulyte, hornblendic, erie epidotic and garnet rocks, were 
in this case a produc a single metamorphic process, acting 
on deposits of lores: iturin age; and, since this wide diver- 
sity of rocks occurs in the eastern or Quartzyte portion alone 
of the limestone area, they have also come from that portion of 
the Lower Silurian to which the Quartzyte group belongs. 
pia setting if the lithological canon is a good one, neither 
of the rocks in the above list can be good for distinguish- 
ing formations ‘of any other geological era than the one here 
conside 
age. And if so, the lithological canon, as far as the varie- 
have not cd it in New England 
hydromica schists of the series we wor distinguishable from 
those of many other geological re 
The lithology of the region ae “still some Lagesage oo 
These are: the absence of hornblendic granite, and syenyte; 
the sparing occurrence of hornblende schist and horublendic 
gneiss, these rocks occurring only in beds subordinate to er 
mica schist or true gneiss; the absence, so far as observed, of 
labradorite rocks; and the certain absence of granitoid labra- 
dorite rocks (those having cleavable labradorite as a prominent 
