273 Prof. Rogers's Address before the 



erosion of the rocky floor, were produced by currents of the nature of 

 broad shallow rivers, and that subsequently the land subsided and con- 

 tinued beneath the ocean long enough for the deposition of the Cham- 

 plain tertiary, upon which the icebergs at the same time brought bowl 

 ders from the north to form the upper or later drift.* 



The hypothesis of a general depression of the surface at the detrital 

 epoch is objected to by Mr. Vanuxem, who has himself been a careful 

 explorer of the phenomenon of the drift in New York, on the ground 

 that " the absence of all marine productions whatever, excepting those 

 which form a part of the materials of the alluvium, (meaning the post 

 pleiocene clays,) is in opposition to any but a very transient submer- 

 sion." This argument, as I have already intimated, appears to me con- 

 clusive. The whole method of geological reasoning requires, that we 

 should find a marine deposit before we can assume the presence of the 

 ocean, while analogies derived from every other geological period show 

 that in the supposed condition of general submergence, the great, steady 

 currents which floated those fleets of icebergs must also have wafted 

 in some sedimentary matter and left continuous strata, however thin, 

 of clay, fine sand, or marl, if not every where, at least in the more 

 tranquil tracts of that extensive sea. Yet not even outside of the drift, 

 along its southern border, do we find a trace of any such deposit. This 

 total deficiency of all proofs of a permanent overflowing of the land, 

 must, I think, be viewed as fatal to the iceberg theory. During the 

 progress of the limited post pleiocene marine deposit, it is quite con- 

 ceivable that ice from the neighboring lands did play some part, drop- 

 ping bowlders from time to time on the bed of those inlets of the sea 

 which occupied the present valleys of the St. Lawrence and Lake 

 Champlain ; but these very bowlders I would trace to the adjacent 

 earlier drift. Such icefloes belong in reality less to the epoch of either 

 drift, than to an intermediate one in which the physical circumtances 

 were more nearly those of the present time. 



But if we admit, for the sake of concession, that the wide-furrowed 

 floor of the drift was permanently beneath the water, the explanations 

 given will be found to be still at variance with several incontrovertible 

 considerations. The idea that the icebergs may have come from the 



• Since this address was read, Prof. Emmons has sent to the Association a brief 

 paper, containing, I believe, some essential modifications in his views respecting 

 the origin of the earlier drift. He now attributes it, if I understand him correctly, 

 to a general and rapid movement of waters from the north, the explanation advo- 

 cated for the last three years by my brother and myself. 



