224 MINERALOGY AND LITHOLOGY. 
Orthoclase often appears in these rocks, but only as an unessential 
accessory, though sometimes it is macroscopically visible. Plagioclase 
is not at all rare. Apatite is found ina section of a Portsmouth quartz 
schist. Pyrites is a very common ingredient. It occurs in both micro- 
scopic and macroscopic crystals, which though so small are often very 
well formed. 
A quartz schist from Connecticut lake is very fine in its texture, and 
contains, as accessories, calcite, plagioclase, biotite, magnetite, and chlo- 
rite. Calcite is not rare in these siliceous schists. Its common pres- 
ence in such acidic rocks points toward the gentle action of the forces 
that have effected their recrystallization. This is apparent in all the 
rocks of the region where these schists are most common. 
GREENSTONES. 
Under this head it is proposed to describe those interstratified rocks 
which are so prominent in the valley of the Connecticut, which are inti- 
mately associated together, and which, in common, possess a more or less 
green color that is induced by the presence in them of hornblende or 
chlorite. No especial significance is intended to be attached to the 
word greenstone, though efforts have been made to dignify it with a 
meaning. I use the word simply to connect together for discussion cer- 
tain rocks, which in any lithological classification would be widely sepa- 
rated. As warrant for their union under this term, there is their close 
geological association, and the precedent established by all those who 
have written upon the geology of the valley region, who have so con- 
stantly spoken of greenstone that all will understand what rocks are here 
referred to. 
All along the valley of the Connecticut, from its source to its mouth, 
there are large accumulations of green rocks, and so characteristic are 
they of the region, that the area has always been colored green on geo- 
logical maps. These rocks are of several kinds, and are interstratified 
with one another, with argillitic schists and with other related rocks. 
One kind is the light green chlorite schist, which the microscope shows 
is essentially composed of minute grains of quartz with chlorite. Another 
is the amphibolite, which is composed of amphibole mixed with more or 
