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Association of American Geologisis and Naturalists. 181 
The same gentleman next adverted to the origin: of conglom- 
erates and other coarse mechanical strata, attributing them in 
many instances to the similar agency f the sea-wave produced 
by earthquakes. The wide and uniform distribution of some 
of the coarser rocks of the Appalachian basin, was appealed to 
in proof that they could have been spread out as we find them 
only by a sheet of water as broad as the entire margin of an 
ocean, breaking in successive sea-waves upon the land, and abra- 
ding and dispersing the fragmentary matter during repeated oscil- 
lations of the crust. 
Prof. Rogers then added some remarks respecting grooved 
and polished surfaces at the contact of ancient secondary strata. 
He thinks he has seen unequivocal instances of these in Penn- 
sylvania.. Their production at periods when the earth’s temper- 
ature was manifestly incompatible with the existence of ice, 
would seem to demonstrate that angular detrital matter, urged by 
Water, is able of itself to score and polish the surfaces of rocks. 
Prof. W, B. Rogers continued the illustration of this subject, 
by calling attention particularly to the evidences of ancient denu- 
dation and drifting action, so strikingly displayed along the place 
of junction of the.Oriskany sandstone, (Formation VII, of the Pa. 
and Va. Reports,) and the subjacent limestones, (Formation VI.) 
Tn many districts the limestone has been irregularly denuded, and 
even toa great extent removed, and at the same time fragments of 
the limestone and fossils, water-worn and blended with coarse sand. 
and gravel, have been accumulated to form the lower beds of the 
Oriskany rock. The rapid fluctuation in thickness of the upper. 
limestones, as witnessed in Virginia, Pennsylvania and western 
New York, (near Black Rock, for example,) Prof. R. ascribed 
rather to the irregular force of the denudation, than to irregularity 
of thickness in the original deposit. He dwelt upon the epoch 
of the close of this limestone series, and the commencement of — 
the overlying sandstone, as one of great interest in the history of 
our Appalachian rocks, marked as it is , throughout a great part of 
the Appalachian belt, by evidences of a sudden and great change 
in the physical conditions of the ancient sea, and by the proofs 
of attendant drifting and denuding action of extraordinary energy. 
He contended that the grooved and worn surfaces of the lime- 
stone which mark the abrading action of a drift at this ancient 
period, together with the same phenomena observed in the rocks 
