410 J. D. Dana—Taconic Rocks and Stratigraphy. 
its two (or more) sides, and can be settled in this and other 
cases, only after a careful consideration of all the stratigraphic 
facts. 
The quartzyte of Stone Hill and the quartzytic mica schist 
of Deer Hill, in Williamstown, may be either of the upper or 
lower quartzyte formation, if judged only by the facts the hill 
presents. But the position of these areas, in the Williamstown 
valley, between high ridges of hydromica schist suggest rather 
that it is the underlying Cambrian; and this is to be inferred 
also from the quartzyte spur of the Bennington range reaching 
toward.it from the borders of Pownal. 
The northern end of the Greylock range has an area of 
quartzyte as a continuation of that of Bald Mountain, as stated 
on page 406; and the mica schist near this quartzyte north and 
east of it may be Cambrian, as well as the quartzyte. The 
mica schist has much resemblance to that of the western part 
of Hoosac Mountain; and whatever the fact about the for: 
mer, there is some reason for making Hoosac Mountain Cam- 
brian. In its western part the mica schist is highly arenaceous, 
like much of the mica schist of the Quartzyte formation, and it 
is scarcely less destructible. I know of no evidence from my 
own observations, or from published accounts, that proves it to 
be Archean. Prof. H. Hitchcock long since supposed a fault 
to separate it from the limestone formation of Adams; but the 
fault has not been proved to exist, and, if existing, it is no 
necessary evidence of true unconformability. Farther south, 
between the quartzyte of Cheshire and central Savoy (see map), 
the mica schist is probably, like the quartzyte, Cambrian. 
This subject will be considered again in a following part of 
this memoir treating of the Lower Quartzyte formation. 
5. Conclusion as to the age of the Taconic Rocks. 
When the paper on southern Berkshire was published two 
years since, the evidence as to the age of the Taconic limestone 
and schists consisted in the occurrence of fossils in the eastern 
belt of limestone in Vermont, near Rutland and farther north, 
and in the western limestone and schists of Dutchess County, 
N. Y., near Poughkeepsie and elsewhere. Since then, as 
already reported in this Journal,* the discovery of Lower 
Silurian fossils in Canaan, N. York, has given additional proof 
from the limestone at the western base of the main Taconic Range 
—the localities found occurring within one to two miles of the 
schists of the range, and but ten miles west of Pittsfield, Mass. 
Professor W. B. Dwight joined me in the search there for 
fossils, but did all the finding. The first account of them, by 
* Vol. xxxi, 241, 248, 1886. 
