

272 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- 

 elusive. 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 6f 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 



rflowing of the land, 

 _ theory. During the 

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

 ccivable 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 

 which occupied the present valleys of the St. Lawrence an 

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

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

 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 " furr °* e ftS 

 floor of the drift was permanently beneath the water, the ex P lanatl ° le 

 given will be found to be still at variance with several incontrover i 

 iderations. The idea that the icebergs may have come frorn^ 



brief 



V 



consi 



• Since this address was read, Prof. Emmons lias sent to the Assoc,atl °" *: 



spectmg 



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



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



to a general and rapid movement of waters from the north, the exp a 



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



