m the Southern Old-tertiary. 431 



readily detected in the deposits of the period, which might thus 

 correspond to the Atlantic Miocene. Upon the subsequent 

 irruption of the Gulf Stream through the Antilles chain, the 

 formation of normal marine deposits along the margin of the 

 Gulf would be resumed." 



This and the other hypotheses, to which Hilgard is forced 

 by his observations, appear to me so surprising, that I found no 

 other explanation than that which was expressed by my state- 

 ment, that he accepted the theory of his predecessors as a 

 proved fact. This statement is also attacked with much 

 warmth by Hilgard in his article, but I do not see any reason 

 to withdraw either this or my other statements about his work. 

 In one case, however, Hilgard protests with reason against one 

 of my sentences (p. 65): "Therefore Hilgard made this belt 

 make a sharp curve around Jackson." This may sound, as he 

 understands it, as if he did not find the Yicksburgian south of 

 Jackson, where he maps it. This I d© not wish to say. I 

 withdraw the sentence and replace it by the following: " There- 

 fore Hilgard had here at least to look for a deviation from the 

 regular straight line." 



The only (marine?) shells, so far as I am aware, that are 

 known in the Grand Gulf group, were observed by A. Bigelow * 

 in Alabama. In the lower part of "a sandstone formation, 

 which is quite extensive in the southern part of that State," he 

 observes " very obscure impressions of shells, apparently all 

 bivalves. There are evidently several genera; the outlines of 

 some are quite regular, and in two or three a part of the hinge 

 is discernible." This does not sound like Miocene. Bigelow 

 continues on the next page: "It is questionable whether 

 impressions of shells can be found in any other place than the 

 one I have mentioned." He finishes his article: " The age of 

 this sandstone I am unable to determine; I hope to have the 

 opportunity soon of submitting my specimens to some one well 

 acquainted with fossils." It is to be regretted that Bigelow 

 seems to have found no such opportunity. Can any one give 

 any information in regard to these fossils? 



The Grand Gulf in Louisiana is described by Hopkins. f I 

 fail to see in his report any proof of an overlying of this group 

 over the Vicksburgian. On the contrary, at the southern part 

 of the marine Tertiary belt, in Catahoula parish (p. 16), he 

 states that a bed containing Gorbula alia overlies lignitic beds, 

 and gives an explanation of this fact similar to that of Hilgard. 

 Hopkins's explanation of the absence of fossils in the Grand 

 Gulf is the following (p. 20) : " It is, that the water must have 



* This Journal, II, 1846, ii, pp. 419-422. 



f Second Annual Report Geol. Surv. of Louisiana, 1871, pp. 18-21 



