Association of American Geologists and Naturalists. 181 



The same gentleman next adverted to the origin of conglom- 

 erates and other coarse mechanical strata, attribnting them in 

 many instances to the similar agency of 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. 



Pi^of. 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 YI.) 

 In many districts the limestone has been irregularly denuded, and 

 even to a 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 



