J. D. Dana on the Green Mountain Quarizite. 181 
? 
the beds to the Quebec group on his geological map of Canada. 
The quartzite, however, is still of undetermined relations, some 
regarding it as at the base of the Lower Silurian, and Logan 
placing it at the top. 
propose to state the more important facts which I have ob- 
served in connection with the Green Mountain quartzite at a 
few of its localities, and some of the conclusions which they 
appear to sustain. 
Several sources of uncertainty attend the investigation of the 
quartzite formation. : 
In the first place, there are quartzites of more than one age 1n 
New England, west of the Connecticut river. A Helderberg 
range, whose relation to the quartzite in the gneiss is unascer- 
tained. .We cannot assume, therefore, that this last 1s all of one 
geological age. aoe 
Another difficulty in the way of investigation arises from the 
fact that the quartzite is very generally jointed, and the joints 
are often so numerous and regular that they are ages | mistaken 
for planes of bedding. The only safe course in all cases was 
ound to be, to doubt as to the beddin unless there were 
tal. 
he obliteration of the bedding by impulses of lateral pres- 
sure is well illustrated in the quartzite near Poughquag, 
s, the 
vertical portions, of the whole height of the section ap to 
which have lost entirely the bedding, or division into layers, 
* Pronounced as if spelt Poquaig. 
