292 
GEOLOGICAL APPEARANCES 
the proportion of the schistus to the granite increased, the latter 
penetrating the former in less quantity, and frequently only in narrow 
streaks. But the schistus occasionally changed its dark grey colour 
for a lighter hue, and in these places, when fractured, resembled 
gneiss. Still advancing, I reached the spot where the granite seemed 
to rest on the schistus ; the line of separation being very distinct, 
but interrupted by zig-zag streams of granite which passed from the 
great body of granite into the schistus. 
Below the line of junction, a singular appearance was pointed out 
to me by one of my companions. In a part of the schistus, of a 
lighter colour than its principal mass, appeared two distinct portions 
of their natural dark colour, at some distance from each other, but 
having their opposite edges exactly corresponding. I discovered a 
much more palpable phenomenon, of the same character, in a ravine 
to the left of that in which I observed what I have just described. 
Here a mass of schistus was divided by a vein of granite into two 
portions, the vein passing through it in such a manner as to represent 
the legs of a right angle, the apex of which was in the centre of the 
schistus. In this instance also the two portions of schistus exactly 
corresponded. 
