1894. ] NEW YORK ACADEMY OF SCIENCES. 201 
secondary, and Prof. Judd * enumerates among instances of 
chemical change induced in rocks by the combined influence of 
pressure and ‘high temperature, the production of pyroxene- 
actinolite rims between olivine and feldspar. 
Dr. Adams states that the reaction rims are independent of 
the cataclastic and gneissic structure developed in the rock. 
But the metamorphism due to crushing at great depths may be 
considerably different in character and “effects from the paramor- 
phism due to chemical and molecular action at less depth and 
with perhaps the assistance of water. The two are, it is true, 
usually associated, but either may occur without the ‘other, and 
it is the latter to which, if secondary, the actinolite zones must 
be ascribed. The former m may be said to be more characteristic 
of the Canadian highlands and the Adirondack region ; the latter 
of the bordering ‘and outlying metamorphic rocks ‘along the 
Atlantic coast and elsewhere. 
If the view here taken as to the origin of hypersthene-actino- 
lite reaction rims be correct, one would expect to find, in the 
unaltered rock, olivine with a hypersthene zone but no actino- 
lite. No sections of the St. John gabbros were fresh enough to 
show this, but it may be noted that in the Lizard gabbros Dr. 
Teall} found in one case a pyroxene zone instead of the usual 
anthophyllite and actinolite. 
Prof. Kemp, in an article on Adirondack gabbros{ has given 
a review of the literature of reaction rims ‘around “olivine, to 
which the present writer is much indebted. 
ALTERATION.—Much of this knob is considerably altered, so 
as not to be recognizable except by tracing the successive grada- 
tions to the unaltered parts. The change in appearance of the 
dark silicates is very marked. They are replaced, at first in 
part, then completely, by fine needles of pale green actinolite, 
which appears dark green and satiny in the hand-specimen. 
With increasing alteration this becomes quite coarse and 
bladed, with some schistose structure. The feldspar meanwhile 
has become opaque white, with a tinge of green at the margin, 
and in thin sections shows much actinolite, especially near the 
edge. The last thing to disappear is the mottled appearance, 
and by the time it is gone there is left only a granular to schis- 
tose diorite, composed of small grains of compact dark green 
hornblende, with some feldspar. ‘This rock is indistinguishable 
from the metamor phosed argillites of the Laurentian series. 
* Jour. Chem. Soc., May, 1890. 
+ Loe. cit. 
_{Gabbros from the westera shore of Lake Champlain. Bull. Geol. Soc. Amer., 
Vol. V., p. 213, Feb., 1894. 
