TiiK srctKssioN OF I )i: I "OS ITS. 4() 



uitli the (1('('|» liullows ('\t('M(liii^' (MitWiird t'luiii lli(!ii\('r 

 iiKtiitlis III' (lie Aiiicricau coasts under the dccaii, di' 

 [H'rliaps llicy arc like tlxisc inlcrvciiiii,!;' liclwccii ihc hanks 

 cast u[) hy i\\i'. arctic currents on llie j»rcsent American 

 coast, and like those (U'cp cliannels of the arctic current 

 in th(! Atlantic recently I'Xiilori.'d hy l)r. Cariicntcr. 

 Their arran_t>'('inents ueonruphically, as well as their 

 geolo^yical relations, corres|tond with such \ie\vs. 



The I'ornier consideialion with regard to the ^reat lakes 

 desci'vcs especial notice. Drs. Hunt, Newhcrry, and 

 Spencer ha\e collected many facts to show that the lake 

 basins are connecteil with one another and with tlu; sea 

 hy deep channels now lillcd up with drift-dcjiosits. it is 

 therefore certain that much of the erosion of these hasins 

 may have occurred before the ailvcnt of the ,^laciiil i)erio(b 

 in the I'liocene a^c, when the Aniericiin continent was at 

 a- higher levcd than at present. I )r. Newberry lias _i;'i\en 

 in the l'e[)ort in tlie (ieolo^uy of ( )hio, u lai\t;e collection 

 of facts ascertained by boring or otherwise, which yo far 

 t(j show that were the olil channels (deared of drift and 

 the continent slij^htly (devaled, the ercat lakes would be 

 drained into each other and into the oceun l)y the \alleys 

 of the Hudson and llu! Mississi})iii, without any ro(d< 

 cutting, and if the barrier of the Thousand Islands were 

 then somewhat higher, the St. Lawrence valley nnght 

 have been cut oil' froui the l)iisiii ol the great lakes. 

 Spencer has, howc\er, shown, on the evidence of dilt'eren- 

 tial elevation, that a portit^n at least of the tlrainage of 

 the I'liocene lake country may have found its way d(.)wn 

 the present course of the St. Lawrence valley. 



The latter cause, namely, the possible eroding action of 

 ocean currents, is one more ditticult to estimate, yet 

 5 



