374 Chamberlin and Salisbury — Relationship of 



limit were making their contribution of sand and gravel. In 

 this case as in the other, there would necessarily be northern 

 material in the gravel. . The freedom of the Orange sands 

 from all northern material, therefore, seems altogether conclu 

 sive against the reference of its gravels to the time of the first 

 glaciation, or to any time subsequent to the first glaciation. 



We are not oblivious of statements concerning the constitu- 

 tion of the Orange sand and gravel, which are quite at variance 

 with our own. By implication at least, all geologists who have 

 referred them to the Cham plain epoch, assign them a northern 

 origin. Professor Hilgard thinks the difference between the 

 Orange sand formation and the northern drift, " quantitative 

 rather than qualitative," and that the materials of the two 

 " are essentially correspondent,"* but we have been unable 

 to find any basis in the regions we have studied, for such con- 

 clusions. 



If the position of the Orange sands under first-glacial loess 

 be fatal to their reference to the Champlain epoch, and if their 

 unconformity with the loess, and their " perfect peroxidation" 

 antecedent to the deposition of the loess, be fatal to their ref- 

 erence to an epoch immediately preceding that of the loess, no 

 less does the complete absence of glacial material from the 

 Orange sands and gravels, seem to us to preclude their refer- 

 ence to the ice period, or to any period subsequent to the first 

 ice invasion. We are therefore shut up to the conclusion that 

 the Orange sands are Pre-pleistocene. And even if an occa- 

 sional northern Archaean pebble should hereafter be found in 

 the Orange sand, we should not, on the strength of this evi- 

 dence alone, regard our present conclusion invalidated ; for the 

 drainage basin of the'^fississippi reaches well back into the 

 area of Archaean rocks, and it would not be at all surprising if 

 Archaean pebbles from this source should have found their way 

 into the lower Mississippi Valley before the glacial period, f 



It may be an open question whether the formation below 

 the loess in the region under consideration, immediately pre- 

 ceded the Pleistocene, but it is not the purpose of this article 

 to discuss that question. It is pertinent to the subject here 

 discussed, however, to remark that the conditions of drainage 

 during the first glacial epoch were such as to produce only 

 exceedingly sluggish currents, so far as now known. But the 

 Orange sands, whether of fluvial or estuarian deposition, date 



* This Journal, vol. xli, pp. 313 and 315, 1866. 



f Hilgard says (this Journal, xli. p. 318), that there have been found "rare and 

 well worn pebbles of greenstone, porphyry, trappean rock, and even mica schist. 

 .... among the shingle of the Mississippi band," and raises the question 

 whether they may not have originated from Arkansas. Considering the absence 

 of such material in the gravels of the Orange sand formation farther north, this 

 hypothesis seems plausible. 



