SO-CALLED PORPHYRITIC GNEISS OF NEW HAMPSHIRE 70! 
Archean gneisses and protogenes may also be of igneous origin, 
and their apparent stratification has no connection with sedi- 
mentary or chemical deposition, etc. .... Applying such prin- 
ciples to the classification of the rocks of northern New England, 
we may improve on the report in several particulars. (1) Arch- 
gan rocks are not eliminated from our list. They exist as oval 
areas, such as have been indicated in the Stamford gneiss, and 
south of Mount Killington, Vt., in the Hinsdale, Mass., area, the 
Hoosac Mountain, and elsewhere. I recognize the porphyritic 
gneiss in the Stamford rock, and in the Hoosac tunnel as Arch- 
ean. (2) Our hesitancy about the place of the Bethlehem 
gneiss is met by recent observations. They are batholites, con- 
taining inclusions of the adjacent mica-schists. It does not 
follow that all these protogene areas are of the same character ; 
each one must be studied by itself.’’* 
However satisfactory such conclusions may be in their appli 
cation to most of the formations in the state, a clear statement 
of the true relations of the porphyritic gneiss has not yet been 
made. The author’s recognition of the correct methods which 
must be used in interpreting crystalline schists has as yet not 
been supplemented very largely by their positive exercise in the 
field, and the implication in the foregoing extract that the 
”) 
Archean appears in the state in ‘“‘oval areas,” either igneous or 
non-igneous, is still without demonstration. 
We shall hereafter adhere to the name porphyritic granite, 
for the rock under discussion instead of porphyritic gneiss 
‘which has been so far used. As will appear later, the former 
name, while not embodying all the generalized features of the 
rock, is preferable to the official one of the second geological 
survey. 
Geographical distribution—The porphyritic granite, as shown 
on the survey maps, occupies four large areas with several 
smaller ones. Of these the largest one extends from Mount 
Monadnock, N. 5° E. to the northern flank of Cardigan Moun- 
tain, a distance of sixty miles; while it varies from three to 
*The Geology of New Hampshire. Jour. GEOL., Chicago, Vol. IV, 1896, p. 57. 
