J. D. Dana—Helderberg rocks in the Connecticut Valley. 341 
From the time these ideas were first published, I have had a 
strong desire to learn whether facts sustained them. My strati- 
graphical observations over Western New England, in which the 
Taconic rocks were also studied, were begun some’ years since 
with special reference to the discovery of the truth on this sub- 
ject; and through the whole this object was prominent. The 
examination of the Bernardston region, the results of which 
are here given, was undertaken partly for the same purpose. 
Both have led to the conclusion that— 
Lithological evidence of geological age among metamorphic 
rocks of distunt regions is in general* worse than worthless. It 
is easy to use, and presses itself on the mind most insinuatingly 
when a conclusion is eagerly wanted; and on this account 1t 
be treated with extreme distrust. I have further found 
at— 
The Earth did not finish up its metamorphic work in pre- 
Silurian time, or even by the epoch closing the Primordial, as it 
id not its mountain-making. And this should be so, if, as 
Mallet has demonstrated, the motion attending the uplifting and 
folding of rocks, or mountain-making, is, like other motion, 
transformable into heat. 
It is now twenty-two years since the first announcement, by 
Professor Edward Hitchcock, of the unexpected discovery of a 
ids 
Prof. E. Hitchcock, locates a Devonian sea in central Massachu- 
Setts; and the distribution of the underlying roofing slate was 
regarded by him as indicating the extension of this sea north- 
t 
is Massachusetts. On the accompanying map of part of a 
Wn of Bernardston § the position is marked by the letter 4 
* The excepti ei : i hzean (Azoic) rocks, 
ptions here in view are certain of the earlier Arc 
“i dersthenite and other coarsely crystallized labradorite rocks, the very coarse 
da: 
reddish and dar i -aon-avenite, and chrysolitic rocks. At the 
Same time, it is far Ted Govtatn, that thee rocks are exclusively Archean. 
Hig apy, A rn rer gh 2h 
my: a, on ; bd . ny . * ‘ . * 
Oh Ma map is here tinerted that cuca any have no difficulty in Pes! ee 
Rive. referred to, and so verifying the facts. n is on the at weg 
ont Tailroad ; and its depot is the last stopping place for trains going nor™. Ye 
the ve Vermont. South Vernon is about seven miles by road northea 
mage of Bernardston, but hardly six in a direct line. 
