74 The American Geologist. August, 1902 
Groups of magnetite octahedra are quite con->mon : but there 
is no trace of leucoxene or epidote. Biotite occurs rarely 
in red-brown plates. 
Green chlorite scales are mingled with the actinolite scales 
abundantly. 
It will be noticed that the centers of many of the amyg- 
dules are dark colored. This is from the accumulation there 
of many larger plates of chlorite and needles of actinolite. 
The feldspar is untwinned, perfectly fresh and so free 
from cleavage that it is diflficult of determination by optical 
methods. In pl.ates showing the central emergence of a pos- 
itive axis the extinction was 14 degrees indicating albite, but 
the cleavage against which the measurement was made was 
indistinct; other measurement indicated oligoclase-albite. It 
is sparingly interspersed among the other constituents, but 
fills the cavities sometimes in a granular form that simulates a 
xQvy fine sandstone. ]\Iore commonly it occurs in broad inter- 
lobate fields that show a perfect granophyric structure : ver- 
m^'iorm and clavate lobes of the one penetrate the other ad- 
jacent grains fill them with many isolated grains and rocks. 
This mixture of granophyric plagioclase with chlorite and 
actinolite seems to have been introduced into the cavities by 
heated solutions in much the same way that the similar lim- 
pid and granular albite mixture was introduced into the steam 
holes in the Triassic traps at Cheapside.* 
This original tilling of the amygdules may be thought to 
have persisted while the volcanic rock was altered to a fine 
giained mass of pale hornblende so entirely simple and regular 
in texture that it gives no hint of its original character. 
The large slide shows not the slightest trace of crushing 
and the perfect metamorphosis has been elTerted without any 
iiidication of dynamic infiuences. 
It and the \Miately rock, with which I have compared it, 
are of much finer grain than any other amphibolytes of the 
region. The hornblendes are of the same size, distribution 
and optical properties. The magnitite is of the same dis- 
tribution and shapes and the white granular feldspar mosaic 
is the same in the ground mass of both. The amygdules and 
their peculiar filling are wanting in the \Miately rock, and the 
*See figr. 1, plate vit, in Diabase Pitchstone and mnd enclosures of the Triassic 
Trap of New England. Bui. Geol. Soc. Am., vol. viii, p. 76, 84, 1S97. 
