J. D. Dana on the Quartzite of Poughquag. 251 
mica schist, part of it gneissoid ; and this schist unquestionably 
underlies conformably the limestone. Along the plane of junction 
of the limestone and schist, both here and to the north, occur 
beds of limonite, which are a result of the alteration of iron- 
bearing minerals in the schist, as stated by Percival, the beds 
often retaining in some parts the structure of the schist.* The 
strike of the schist is N. 10°-40° E., and the dip about 50° to 
the eastward. It is a southern extension, as recognized by Per- 
cival, of the schist or slate of Taconic mountain. It has the 
tom a specimen I collected from one of the ridges on the ascen 
of Graylock. 
About a mile and a half southeast of Poughquag (and four 
from Pawling) the mica schist is left for a light-gray fine-grained 
thick-bedded gneiss, partly granitoid. The gneiss has essentially 
the same strike and dip as the overlying mica schist, the 
strike being N. 10°-35° E., and the dip mostly 50° to 60° to the 
* Specimens collected by Mr. Charles A. Brinley at Richmond, Mass. show that 
the principal one of the minerals there altered to limonite is siderite (spathic iron 
or “pla ga of iron). The limestone in some limonite localities is the underlying 
Tock. \ 
“des ter 
ing like a taleose schist, it contains only a 
Sterry Hunt has confirmed this conclusion 
Canada rocks. d : 
I have examined the rocks of Taconic Mountain myself only in Mt. Washing- 
ton. Percival, in his Geological Report of Connecticut, describes — Agee iid Ta- 
i . ; . schis 
8 
o 
oO 
Fs 
(=) 
&. 
oh 
po 
5 
2 
g 
8 
5. 
8 
8 
= 
™m 
chlorite, and yet hs a 
inerals [garnets and staurolites]. This is particularly the case in the south an 
Rortheast part of Taconic Mountain.” 
