396 E. W. Hilgard — Age and Origin 



bly from the same locality, as well as from the gravel beds at 

 Proffit's island, below, that the collection of such gravels, 

 formerly at the capitol at Jackson, Miss., that was destroyed 

 during the war, were obtained. The ledge of ferruginous 

 gravel conglomerate is underlain (as seen at the landing a mile 

 above) by a bluish clay of the peculiar aspect and texture of 

 the typical Grand Gulf Tertiary, which is everywhere else 

 overlain by the Lafayette. We thus appear to have in the 

 Natchez profile the usual regular sequence, in full, of Grand 

 Gulf, Lafayette, Port Hudson beds with calcareous nodules, 

 " Sand Loess," calcareous (typical) Loess, and brown surface 

 loam. 



It has seemed to me, from the outset, but natural that the 

 larger crystalline gravel, coming from beyond the barrier of 

 Carboniferous rocks above Cairo, should remain within a short 

 distance of, or entirely within, the deep central channel which 

 has always coincided closely with the Mississippi trough of to- 

 day ; while the flood waters carrying the lighter gravel and 

 sand would spread over the uplands, laterally, where after- 

 wards, by long subaerial exposure, the small crystalline gravel 

 would disappear completely by weathering, as indicated by the 

 very " rotten " condition of the same class of gravels at Natchez 

 and Proffit's island. To my mind it would.be rather sur- 

 prising if such pebbles had survived up to this time in the 

 upland or lateral portions of the Lafayette deposits ; it greatly 

 surprised me to find them as far south as Petite Anse, for 

 although small and much decayed, there still were some of 

 several ounces weight. I do not therefore see that the absence 

 of crystalline moraine gravels from the lateral portions of the 

 Lafayette in Tennessee, Mississippi and Louisiana, even if as 

 complete as has been thus far supposed, has the weight assigned 

 to it by Chamberlin and Salisbury (this Journal, xli, 859, 

 who contend that on that ground alone the formation must be 

 referred to a period preceding the glacial epoch — inferentially, 

 the Tertiary ; the same observers having found the loess to 

 contain essentially the materials of the Illinois moraines, while 

 the gravels which they consider as contemporaneous with the 

 "Orange Sand" and which they find to reach as far up as 

 Keokuk, are free from such material and are evidently pre- 

 glacial. On the other hand, Call, in his discussion of the 

 formations of Crowley's ridge in Arkansas, refers certain 

 gravels found there to Quaternary time and identifies "Hil- 

 gard's Orange Sand" with underlying deposits in which he 

 finds unquestionable evidence of Eocene age. He is clearly 

 mistaken as to the nature and identity of the much-discussed 

 formation so designated by me ; which as he should have 



