Fic. 2.—A tragment of the chloritic rock showing, diagrammatically, stretched 
and dislocated veinlets of quartz. One-third natural size. 
main argument,—the disseminated grains of quartz in the 
chloritic rock. To begin with, the free silica or quartz appears 
to be wholly or almost wholly wanting in a considerable portion 
of the chloritic rock; and it is probably this materiaf that is 
represented by Mr. Smyth’s analysis. A considerable part of 
the quartz, also, occurs, or has occurred, in the form of veinlets, 
Fic. 3.—Another fragment of the chloritic rock showing, diagrammatically, 
angular inclusions of quartz, the most of which, at least, are probably 
due to the comminution of quartz veinlets. One-half natural size. 
varying from a line to possibly an inch or so in width. Al- 
though undoubtedly secondary features of the rock, the veinlets 
clearly antedate the final or complete alteration ; and especially 
do they antedate a large part of the hydration, expansion and 
consequent slickensiding of the mass, for they have been very 
extensively broken, dislocated and even granulated by this dif- 
ferential movement. The chloritization or greenstone altera- 
tion of a trap, it is well known, involves the liberation of a 
large amount of silica, which commonly takes the form of vein- 
lets in the rock, and then during the later stages of the alter- 
ation the veinlets may be broken and disarranged. How com- 
plete the destruction may be is well shown by figures 2 and 3, 
