of the Lafayette Formation. 899 



as truly constitute the beginning of a new era — the Quaternary 

 — as the incipient glaciation of the continent. 



I have heretofore suggested that the extraordinary change of 

 character from the Vicksburg to the Grand Gulf epoch — the 

 substitution of brackish and fresh-water features for the ex- 

 clusively marine — may have been caused by a diversion of the 

 Gulf Stream to the outside of the Antilles, leaving the present 

 Gulf as a receptacle for the continental waters, by the con- 

 tinued influx of which at least the north-shore deposits must 

 have been sensibly freshened. However that may be, it is indis- 

 putable that from some cause there was a great increase of 

 fresh- water influx during the Grand Gulf epoch ; and a still 

 greater one during that of the Lafayette, completely excluding 

 marine features from that formation, even where its beds 

 actually project into the waters of the Gulf. 



I, with Tuomey and others of the older geologists, have 

 sought the origin of this increase of fresh-water influx in the 

 melting of the continental glacier ; and on the evidence before 

 me of the actual translation of moraine material to low lati- 

 tudes by such influx, and manifestly on a much steeper slope 

 than now exists, or could exist during a period of submergence, 

 I have attributed the Lafayette formation to a period of high 

 elevation rather than one of depression ; conceiving such eleva- 

 tion, greater in the northern latitudes, as a possible cause of 

 glaciation. 



As to the extent of such elevation, I have in former papers 

 shown that, adding to the present maximum altitude of the 

 loess summits in Louisiana (450 feet) the greatest depth at 

 which gravel had then been found below sea level (in the 

 bored wells of Calcasieu), viz : 450 feet, we obtain 900 feet as 

 the minimum amount of the oscillation which has occurred 

 since the gravel reached the Gulf shore. I am now enabled 

 to increase this figure to 1200 feet, the gravel bed having been 

 reached at the depth of 760 feet in the latest borings made at 

 New Orleans. In this estimate no allowance is made for the 

 degradation of the land surface, that has occurred since the 

 deposition of the loess. 



But if the Lafayette gravels are found at the depth of 760 

 feet below sea level at New Orleans, it follows that at the time 

 it was deposited, the land was not submerged, but stood higher 

 at least to the extent of that same depth. The only escape 

 from this conclusion is to prove that this gravel, together with 

 that of the Calcasieu wells, and inferentially that of the 

 Natchez profile, is not a part of the Lafayette at all but belongs 

 to the Port Hudson epoch. 



Admitting this for the sake of argument, where do we 

 stand ? We are then forced to conclude that at the beginning 



