THE OLD RED SANDSTONE. - 219 
red. It contains pebbles of small-grained, red granite, red 
quartz rock, red feldspar, red porphyry, an impure red 
jasper, red hornstone, and a red granitic gneiss, identical with 
the well-marked gneiss of the neighboring Sutors. This last 
is the only rock now found in the district, of which fragments 
occur in the conglomerate. It must have been exposed at 
the time to the action of the waves, though afterwards buried 
deep under succeeding formations, until again thrust to the 
surface by some great internal convulsion, of a date compar- 
atively recent.* 
The period of this shallow and stormy ocean passed. The 
bottom, composed of the identical conglomerate which now 
forms the summit of some of our loftiest mountains, sank 
throughout its wide area to a depth so profound as to be little 
affected by tides or tempests. During this second period 
there took place a vast deposit of coarse sandstone strata, 
with here and there a few thin beds of rolled pebbles. The 
general subsidence of the bottom still continued, and, after a 
* The vast beds of unconsolidated gravel with which one of the 
later geological revolutions has half filled some of our northern val- 
leys, and covered the slopes of the adjacent hills, present, in a few 
localities, appearances somewhat analogous to those exhibited by this 
ancient formation. There are uncemented accumulations of water- 
rolled pebbles, in the neighborhood of Inverness, from ninety to a 
hundred feet in thickness. But this stratum, unlike the more ancient 
one, wanted continuity. It must have been accumulated, too, under 
the operation of more partial, though immensely more powerful agen- 
cies. There is a mediocrity of size in the enclosed fragments of the 
old conglomerate, which gives evidence of a mediocrity of power in 
the transporting agent. In the upper gravels, on the contrary, one 
of the agents could convey from vast distances blocks of stone eighty 
and a hundred tons in weight. A new cause of tremendous erergy 
had cnme into operation in the geological world. 
