270 Prof. Rogers's Address before the 



those geologists who have recently written upon our drift. Never- 

 theless^ the doctrine which ascribes the transportation of the bowlder 

 matter to icebergs driven by currents over a permanently submerged 

 surface, finds evidently the greatest number of advocates. Some geol- 

 ogists however, believing this hypothesis insufficient to explain the 

 phenomena, appeal to the theory which supposes a series of munda- 

 tions of the land engendered by a violent paroxysmal movement of all 

 the northern latitudes. Permit me to examine briefly some 01 the 

 principal features in these doctrines, and the leading arguments con- 



nected with them. 



An extensive submergence of all the northern tracts of the continent 



is of course implied in the supposition, that the detrital matter has been 

 floated to where it now rests by icebergs. Thus Prof. Hitchcock who 

 thinks that the greater part of the phenomena must be explained by 

 icebergs, conceives that nearly the entire surface of the land must have 

 been beneath the level of the sea, and against the opinion that diluvial 

 currents could have rushed across the continent while it stood at nearly 

 its present elevation, he objects that the assigned causes for such, are 

 insufficient to send an ocean to the summit of our mountains, five or six 

 thousand feet above its proper horizon. ^ 



Mr. Hall in like manner, urges that no explanation of the mo eo 

 transport of the bowlders reconcilable with their present situation, can 

 be offered, which does not assume that the whole surface was perma- 

 nently covered with water,* and he thinks that a depression below 

 present level of as much as two thousand feet, is required for the trans^ 

 port and deposition of the bowlders forming the later drift of sout e^ 

 New York. He is led to the conclusion, that they were " not move 

 by any powerful flood." He supposes that the " mountain . cham f ^ 

 New England and New York formed long ranges of islands rising ro^ 

 the ocean to two or three thousand feet above its level, their si es 

 ered with perpetual snow and glaciers, and their bays termina c ^ 

 cliffs of ice from which detached masses floated off, bearing wit ^ 

 bowlders and fragments of rocks," and he thinks, " that it can ^ 

 monstrated that this dispersion of the bowlders and fragments con in^ 

 for a long period, while the land was rising from the ocean. ^ 



the land had risen to within eight hundred or one thousand feet o ^ 

 present elevation, the great valley of Lake Ontario would form ^ haffk 

 bay communicating with the ocean through the valleys of t e 



• See page 336 of Mr. Hall's Rep. Geol. New York 



