﻿496 S. V. Wood,jun. — American, and British Surface- Geology. 



1000 feet below the sea-level ; and as this must have brought the 

 sea very high up the valley, its recession was a long affair, and the 

 mud of the Bluff formation consequently represents the long period 

 of this recession which its outspread accompanied, the portions at 

 higher elevations being the oldest. He adds that this submergence 

 brought the waters of the Gulf of Mexico up the valley of the 

 Mississippi until the sea covered all the lower half of Ohio ; and 

 that it was during the maximum of this submergence, and during 

 the acccumulation of the beds 'da, that the action of the shore- waves 

 formed the Kames and Eskers which occur on the watershed be- 

 tween the two basins ; but, as I have before observed, if the sea had 

 thus overflowed the water-parting, we are met with the difficulty 

 that the waters of the lake-basin would have become salt, of which 

 no evidence is offered. Neither does Prof. Newberry offer us any 

 evidence of marine organisms to prove the occupation of the upper 

 parts of the Mississippi valley by the sea. He describes certain 

 clays with sands and gravels, which, occurring in Southern Ohio, 

 belong to the deposits of the Mississippi basin ; and these, he says, 

 overlie a forest gi-owth, which seems to be a continuation of that 

 which, lying within the St. Lawrence basin, occurs over the Erie 

 clay, and appear to be identical in age with the beds 3a. The 

 relation which these clays, etc., bear to the Bluff formation of the 

 Mississippi, he does not point out with sufficient clearness to enable 

 me to apprehend precisely his view about them, but so far as I can 

 gather from his memoir (p. 37), he regards thein as the equivalent 

 of that formation. If, however, the depression about New Orleans 

 was coeval with that to which the marine clays of the Lower St. 

 Lawrence and of the Atlantic coast are due, the Bluff formation 

 would seem to have begun before this. Looking at the subject in 

 the whole light afforded by the examination of the Glacial features of 

 the St. Lawrence basin, as described by Prof. Newberry, it seems to 

 me that the Bluff formation of the Mississippi valley must represent 

 both the Glacial and the post-Glacial periods, and have commenced 

 as far back at least as the Erie clay. Indeed, if the suggestion that 

 the Kames and Eskers of the water-parting between the two basins 

 in Ohio originated from the subaerial dissolution of the ice of the 

 first sheet, when it rested there before shrinking back into the St. 

 Lawrence basin, and forming a lake, be sound, the finer mud carried 

 off by the water in forming such Eskers and Kames must have 

 found its way into the Mississippi valley, and contributed to the 

 material of the earlier part of the Bluff formation, whatever sub- 

 mergence the Mississippi valley underwent having been confined 

 to its lower or Gulf extremity.^ 



1 In reference to this suggestion it would be interesting to learn to what extent 

 rock-fragments have been found in the Mississippi valley which can be identified 

 with rocks in situ in the St. Lawrence area. Prof. Newberry speaks of large 

 quantities of gravel and boulders having been carried through the waste weirs, 

 penetrating the water-parting, and deposited in lines leading towards the valley of 

 the Ohio, so that I infer such rock-fragments of lake-basin origin do aboiuid within 

 the limits of the Mississippi valley, and up to the line of Northern drift limit shown 

 in the map. 



(To be continued in our next Number.) 



