No. 161.] 
169 
of debrisj forming a sloping talus. The lively and contrasted co- 
lors of the sandstone add to the picturesque beauty of the third 
fall, near Carthage, and the vast chasm, with its mural precipices 
attests the mighty agency of a cataract, which, by disintegrating 
its rocky bed, slowly recedes up the stream and scoops out a deep 
gorge of several miles in length. The two lower falls of the Ge^ 
nesee are far less elevated than the upper one near Rochester, 
which is 96 feet in height, projecting at the summit, and thus cast- 
ing a grand unbroken mass of water to a considerable distance from 
the base of the rock. This difference in the falls is owing to the 
nature of the strata, which, at the two lower cascades, are com- 
posed of sandstones and slates, many of the layers being friable 
and readily yielding to the force of the current, whilst the great 
cataract has receded until it met a limestone extremely hard and 
compact. This has protected the slates and sandstones beneath, 
and now prevents the bed of the river from being worn away with 
the rapidity of former times. This operation, however, will be 
facilitated by a measure now contemplated of giving a greater 
inclination to the bed of the river above the fall, in order to per- 
mit the water in time of freshets to subside more rapidly than at 
present. In its manner of retrocession this fall closely resembles 
those of Niagara, which, as was first observed by Mr. Eaton, must 
recede more and more tardily the nearer they approach to lake 
Erie, in consequence of the greater thickness of limestone, which 
every new fracture will expose. The same strata have been di- 
vided both by the Niagara and Genesee rivers; allowing for the 
diflference in size and extent, the gorges are very similar, and the 
falls of both rivers commenced their career at the same geological 
epoch, when, in consequence of the rupture of its ancient barrier. 
Lake Ontario subsided to its present level. On the Genesee the 
lowest rocks consist of the predominating red variety of the vari- 
egated sandstone, of which about 80 feet are exposed. It is com- 
posed generally of a mass of nodules of various sizes, alternating 
with layers of more compact rock, and the former is so friable that 
a slight touch is sufficient to detach a mass from the cliff. The 
summit of the sandstone is composed of a gray variety, about four 
feet thick, termed Gray BancC^ by Mr. Eaton, some portions of 
which very slightly effervesce with acids. Among the innumerable 
fragments of sandstone which constitute a portion of the talus be- 
neath, Fucoides Brongniartii occurs, the species common at Medina 
and Oswego, and characteristic of the same series of strata in Penn- 
[Assem. No. 161.] 22 
