J. D. Dana—Helderberg rocks in the Connecticut Valley. 351 
after the Lower Silurian. Facts are against any earlier epoch ; 
and the only other probable suggestion is that the time was 
ter the Carboniferous age, when the Alleghanies were made. 
Hence, the various Helderberg rocks of the Connecticut Valley 
have their actual date as crystalline or metamorphic rocks either 
rom the close of the Devonian, or that of the Carboniferous era. 
The conclusions which have been presented are based on a 
foundation of facts—certainly as far as the region of Bernards- 
ton, Vernon, Northfield and Hinsdale is concerned, where my 
own observations were made; and, judging from the — 
tions of Prof. Hitchcock, they appear to be sustained as regards 
the Cods range to the north. 
I now pass to what is at present hypothetical, since I can 
appeal only to the observations of others, and they are not 
sufficient in detail for positive conclusions. I propose to ex- 
amine the region personally, another season. 
2. The Connecticut Valley in Massachusetts. 
The region of the Connecticut Valley, south of Vermont and 
New Hampshire, commencing in the northern towns of Ber- 
nardston and Northfield, iscovered to a breadth of ten to twenty © 
miles with the Triassico-Jurassic Red Sandstone formation ; so 
that the opportunities for observing the continuation of the 
More northern formations southward are thus much restricted. 
Still there are pertinent facts on record. : 
In the geological map of Massachusetts connected with Hitch- 
cock’s Report, the hornblendic rocks of South Vernon and 
Northfield are made to extend southward in two lines, one 
south of South Vernon, passing by Leverett, Amherst and 
Granby, the other south of Northfield, through seat RARE 
. 
Belchertown, Palmer, Monson and Wilbraham, eac line quite 
slate occur with the hornblendic rocks, as at the north. Quartz- 
ite is spoken of as occurring with the hornblendic rock of 
Northfield, Palmer, Monson and Granby. tas 
‘he varieties of rocks described by Hitcheock are similar to 
those of the Vernon and Northfield region, excepting that no 
3. The Connecticut Valley in Connecticut. 
In Connecticut the Connecticut Valley terminates at New 
Haven Bay—not at Saybrook. The river leaves the great cen- 
