AND THE SALT DEPOSIT ON PETITE AXSE ISLAND. 29 



at a distance from any great channel, the drift pehblcs occur at a depth of four 

 hundred and fifty feet: it cannot be surprising that at the grand outlet of the con- 

 tinental waters, they should lie a few hundred feet deeper. 



THE DRIFT PERIOD, SOUTH AND WEST. 



Assuming for the present that tlie four hundred and fifty feet r(^])resent the; 

 maximum depth at which the drift is found on the Gulf coast, it would seem 

 necessary to assume, in order to account for the transportation of the northern 

 pebbles to that latitude, an elevation of the Gulf coast by nearly that amount above 

 the general sea-level, at the time the transporting currents began to flow. So far 

 as I am aware, the transportation of large pebbles is practically confined to streams 

 of shallow water. Deep currents riu'gJd, of course, assume a velocity sufficient to 

 transport them ; but I fail to remember any actual case of the kind, save perhaps 

 in the sudden breaking of dykes, natural or artificial. And even then, transporta- 

 tion must substantially cease so soon as a large reservoir, or tlu^ sea, is reached. 



It might be said that, since just before the Drift period the Gulf of INIexico was 

 disconnected from the ocean, its level may have been difl:crent from that of the latter. 

 Such may have been the case; but if so, the level of the Gulf, forming the common 

 reservoir of the continental waters, could only have been higher, but not possibly 

 lower, than that of the ocean. The above estimate of the amount of upheaval can- 

 not, therefore, but be a mininnim. And whatever may ultimately be found to be 

 the maximum depth at which the drift pebbles lie beneath the Gulf level, m.ust be 

 assumed as representing, approximately, the amount of elevation during the Drift 

 epoch. Moreover, in order to account for the transportation of coarse materials, 

 the general southward slope of the country must be assumed to have been greater 

 than is the case at the present time. Hov/ far these phenomena of elevation may 

 go to account for a glacial epoch at the North, we can at present but conjecture; 

 yet it cannot be questioned that even Ae minimum of probable uprising might 

 liave essentially aided in accomplishing the result, which a cutting off of the Gulf 

 stream or Kuro Siwo from the Arctic ocean might, alone, have been inadequate to 

 bring about.^ 



As regards the origin of the great flood which has been instrumental in covering 

 so large a portion of the States bordering on the Lower ^lississippi, witli sand and 

 sliingle derived from higher latitudes, Tuomey and myself have early suggested 

 that it might liavc been the result of the melting of the northern glaciers; in con- 

 sequence, perhaps, of a rather rapid depression. In the former portion of the 

 hypothesis I still substantially believe; for it is obvious, from both the litliologieal 

 and pala^ontological features of the southern Drift, that no marine current could 

 have been concerned in its formation. But as regards the second part of the sug- 



' Some of the "Western geologists are emphatic in stating that they "find no reason to suppose an 

 elevation of the continent during the Drift period." It is not easy, indeed, to see how direct jiroofs 

 of such an event could exist, to a verv obvious degree, in Ihe interior of a continent. 



