400 E. W. Hilgard — Age and Origin 



of the Port Hudson epoch there existed the elevation of the 

 continent which I have conjecturally assigned to the Lafayette 

 time. According to Chamberlin and Salisbury, the loess, in- 

 dissolubly connected with the Port Hudson, derives its mate- 

 rials from the continental moraine ; and the Natchez profile, 

 showing the moraine gravel lying at the base of the Port Hudson, 

 conclusively settles this point. If then, as McGee contends, 

 the Lafayette was formed during a period of submergence, it 

 would be necessary to assume a reelevation of the land prior to 

 the beginning of the Port Hudson period, which, with the 

 loess and overlying loams, manifestly represents a subsequent 

 period of depression, coincident with the melting of the 

 glaciers. The variations of materials within this Port-Hudson- 

 Loess-Loam (" Columbia ") series should, then, in some measure 

 indicate the advances and recessions of the continental ice 

 sheet. 



The question is whether the " Orange Sand " of the Embay- 

 ment does not represent the first period of recession and ice- 

 melting, and the Port Hudson (or Columbia) series the second 

 and final one. Under this point of view, instead of the double 

 oscillation postulated by McGee, the land would simply have 

 risen at the end of the Tertiary (Grand Gulf) period, assuming 

 at the north a considerably greater altitude than at the south, 

 as is postulated by the transportation of such large gravel to 

 the margin of the Gulf. I gravely question that any such 

 extreme elevation as has been suggested as necessary by 

 Chamberlin (8,000 to 10,000 feet) would even now be required 

 to re-glaciate the northern United States. Half of these fig- 

 ures would come nearer my estimate of the probable require- 

 ments, provided the rise extended into the arctic region, as is 

 the case in Greenland. 



It seems to me that, had the Tertiary climatic conditions 

 (which in the Grand Gulf beds are made manifest by the ex- 

 tended prevalence of tree palms) continued during the Lafay- 

 ette period, we could not help finding in its deposits the same 

 evidences of a subtropic forest growth at some points. But 

 no such evidences exist ; all the fossil woods thus far identified 

 and found within the Lafayette beds are derived from the 

 underlying Tertiary, even though the process of silicification 

 has probably occurred during Lafayette time, concurrently 

 with the formation of the curious local masses of siliceous sand- 

 stone, which show plain intrinsic evidence of the intrusion of 

 siliceous solutions into beds of loose white sand. In these at 

 least, remnants of the peculiar plants of the period might be 

 sought; but a few indistinct indications of what might be con- 

 strued into roots or grass leaves are the only vestiges observed 

 by any one. In the superficial paludal beds to which McGee 



