348 J. D. Dana—Helderberg rocks in the Connecticut Valley. 
to 28°, with the strike 5. 20°-380° E. But, at both H’ and E”, 
itself in places micaceous, and then becomes true gneiss. 
little north of EK’, the gneiss is well-characterized ; and it is an 
old-looking kind, that might be thought pre-Silurian by a 
believer in the lithological test. The outcrops on the ridge 
too plain for the strongest doubter to questio 
This adds to the Helderberg series, gneiss in extensive strata, 
another of the rocks observed at South Vernon. From the 
relative position of the quartzite and underl ee gneiss in the 
ridge EK’, and the slate in the valley over a hundred feet below, 
the : mica slate must be an. inferior bed in the series, unless there 
is a fault. 
slabs of it a few Steep of the So representing 
among them both of the known kinds of tv 
This adds staurolitic slate to the fickiodeeg series of Central 
New England, 
We are now prepared for our conclusions 
1. This Helderberg series in Central New England comprises 
a large part of the common kinds of metamorphic rocks, gneiss 
of several varieties, undistinguishable lithologically from the 
oldest; hornblende rock and schist; syenitic gneiss; coarse 
mica schist and mica ann: staurolitie slate 
large part of the rocks that have been distinguished as 
of the “Montalban” or “ White Mountain series” in New Ha 4 
shire, and regarded of pre-Silurian age, are here included, am 
are hence nothing but altered Helderberg sediments. It is 
henee far from true that “the crystalline rocks of the Green 
Mountain and White Mountain series” and ‘the whole of our 
crystalline schists of Eastern ener America are not only pre 
Silurian, but pre-Cambrian in a dif. 
3. The passage of poaeingpe at ies is exhibited in @ 
ferent ways. The presence of mica in the quartzite 1s pers 
the steps But, at the locality marked g on the map, sae the 
quartzite is very finely banded with white and gray, @ : 
The 
* Hunt’s Address before the American Association in 1871, pp: 8, 3 ee in- 
rocks referred to the “ White M in series” are stated, i he gses” and 
clude “well defined mica schists interstratified with neg sag « peds 
every variety “do fine-grained schist which *nirnblende 
f wn toa s in oh horn! 
f micaceous quartzite,” ‘ dark-colored gneisses snd neg | in whi h rablen® 
takes the place of mica,” bia “ pass occasiona ally = ba lee 
: i s;” “beds of estan i tise ne stau- 
which are intimately Sasttladed — the highly micaceo schists containing 
Tolite, andalusite, cyanite and garn 
