J. D. Dana—Tacome Rocks and Stratigraphy. 275 
limestone belt, which has there a width of 84 miles, comes, on 
the south, bluntly against the high range of hills of Sharon, 
Cornwall and Kent, and sends off a southward branch either 
side; this obstruction is the occaszon of the subdivision of the 
lmestone into two branches, mentioned on page 271, one in 
eastern New York to Towner’s, the other in Connecticut to 
New Fairfield. Now, this range of hills has much quartzyte 
in some parts over the northern end, and also, beyond the 
quartzyte, gneisses and other rocks, part of which at least 
(as chondroditic limestones, and other characteristics show) are 
Archean. Archean hills which antedate in uplift and erosion 
the limestone seem to have determined in tis case the shore 
lines of the early Paleozoic seas, and the area of limestone- 
making in the waters. At the southern end of this Archzean 
range (Percival’s K1) the two branches of limestone, as Perci- 
val first pointed out, make a junction across from Dover to 
South Kent, which is about half the way to Towner’s and New 
Fairfield ; thus binding in one mass the chief range of Canaan- 
Salisbury hmestone that goes to Towner’s with the more east- 
ern part that goes to New Fairfield, although the latter has its 
course among mica schists and gneisses. 
e. Another region of abrupt change in the Taconic outlines 
is that of Pittsfield, at the summit level of the great valley of 
Berkshire. The height of the wide plain is about 1,000 feet 
above tide level. It is the place of union of the headwaters of 
the Housatonic River. The longest of the tributaries, which 
carries the name of the river, comes in from the eastward along 
the valley which is made use of by the Boston & Albany rail- 
road. For this and other unexplained reasons, the Pittsfield 
plain spreads eastward of the usual limestone-limit (as the map 
shows) by more than a mile; and it is equally remarkable that 
while, both to the north and south of Pittsfield throughout 
Berkshire, the limestone area is intersected from north to south 
by two or more ridges of schists, the Pittsfield region, for a 
breadth from north to south of four miles, isall limestone, from 
the Taconic range on the west to the eastern limit in Dalton. 
Further, this eastward extension of the Pittsfield part of the 
limestone area is accompanied by a long eastward extension 
also of the quartzyte formation adjoining it; this formation 
occurring to the southward of the extension over a large part of 
northern Washington, to and beyond Ashley Lake, and from 
there returning westward to Dewey’s Station ; and less widely 
to the northeast of the Pittsfield plain. Moreover, within two 
or three miles east of the quartzyte formation occur zircon- 
bearing hornblendic rocks, and in one region (in Hinsdale) 
chondroditic limestone, giving definiteness to the indications of 
Archean age. 
