168 THE CANADIAN NATURALIST. [Vol. vi. 



It appears that the oldest Post-pliocene deposit in the south is 

 that called by Prof. Hilgard the " Orange Sand." This deposit 

 is spread over the States of Mississippi, Alabama, Tennessee, and 

 parts of Louisiana, Kentucky, and Arkansas, and in some places 

 attains an elevation of 700 feet. It contains water-worn frag- 

 ments of northern rocks, and is supposed by Prof. Hilgard to 

 have been deposited by rapid currents of water, possibly fresh, as 

 the deposit contains no marine fossils. 



Above this, according to Prof. Hilgard, is found in places a 

 swamp, lagoon or estuary formation designated the " Port Hudson 

 group." Succeeding this is the " Bluff or Loess " group, a deposit 

 of fine silt, limited almost or entirely to the Valley of the Missi- 

 sippi. Its maximum thickness is seventy-five feet. 



On this rests a very widely distributed bed, the " Yellow 

 Loam," not more than twenty feet thick, but much more exten- 

 sively distributed laterally than the former, and reaching an ele- 

 vation of 700 feet. 



Under the names of "Second Bottoms or Hummocks," and 

 " First Bottoms," are known terraced deposits of clay belonging 

 to the present river valleys, but indicating in the case of the 

 Second Bottoms a greater amount of water than at present. 



It is obvious that all of the above are aqueous deposits, and 

 there seems to be no evidence whatever in the region referred to, 

 of the action of land ice, though the stones and few boulders in 

 the Orange sand are very probably due to floating ice. There 

 seems reason to believe that the Orange sand is continuous with 

 the Boulder-drift of the north-west ; and if this is, as stated by 

 Newberry and others, a later deposit than the Erie clay, then it is 

 probable that no representative of the latter exists to the south- 

 west, or that the Orange sand represents the whole of the northern 

 deposits. In any case it represents northern currents of water, 

 though whether salt water admitted by the depression of the 

 land, or fresh water resulting from the melting of glaciers, it is 

 not easy to decide, as very great difficulties attend either view 

 in the present state of our knowledge of the deposit. What- 

 ever the conditions of deposit of the Orange sand, it would 

 seem to have been succeeded by a land surface, and this 

 by a depression to the extent of 700 feet or more, before the 

 modern elevation of the land. If this last elevation corresponds 

 with that of the terraces of the St. Lawrence, then the former one 

 must have occurred in the St. Lawrence valley in the interval 



