in the Southern Old-tertiary. 429 



does not make now the simple conclusion, that the Vicks- 

 burgian overlies the Grand Gulf, but he argues : as the 

 Vicksburgian overlies these strata, they cannot belong to the 

 Grand Gulf, they must belong to the Vicksburgian. These 

 strata have precisely the characters of the Grand Gulf group, 

 and Hilgard says expressly: " and so I referred them until I 

 found them overlaid by a siring of limestone nodules containing 

 Orbitoides, about forty -five feel above the uppermost sands of the 

 Viclcsburg group." Limestone with Orbitoicles is certainly ma- 

 rine Tertiary and is considered by Hilgard always as Vicks- 

 burgian. Therefore I fail to see not only why he does not 

 conclude from this observation that the marine Tertiary over- 

 lies the Grand Gulf, but also why he does not mention it as a 

 case where the Vicksburg group "dips up," or has a northern 

 dip, since this follows from his statement of the heights. 



If Vicksburg is at the top of the marine Old-tertiary we 

 should expect to find below it the Jacksonian and Claibornian. 

 AVe cannot expect to find exactly the same species as at Jack- 

 son and at Claiborne ; for during the Jacksonian and Claiborn- 

 ian time a different fauna may have lived in Vicksburg, con- 

 sisting perhaps of a few species only. But what we have to 

 expect is to find at least marine Tertiary. What is, however, 

 the base of the Vicksburg Tertiary at Vicksburg? I have not 

 observed it, but according to Hilgard, I, p. 141, there are below 

 my " Lower Vicksburgian" at first " 25 feet of gray or black lig- 

 nitic clays or sands with iron pyrites, exuding salts and sul- 

 phuretted hydrogen." Then "3 feet solid, lustrous lignite, 

 with whitish cleavage planes," and then follows the top of a 

 limestone without fossils. This is what we should expect 

 according to my profile — lignitiferous strata without marine 

 fossils; even the salt, which according to Hilgard (I, p. 148) 

 characterizes the Grand Gulf, is not wanting. 



What is under the Jacksonian at Jackson and neighborhood? 

 We find (I, p. 123): "In the wells bored in South Madison by 

 the Rev. Mr. Lambuth, the fossiliferous marine strata of the 

 Jackson group were passed through at about 90 feet, after 

 which 'blue dirt,' with selenite, several ledges of sandstone 

 and a lignite bed of 40 feet thickness were struck, but no more 

 marine strata were reached at a depth of 415 feet." We see 

 here that the non-marine lignitiferous strata, which crop out at 

 a few places in Vicksburg, appear here near Jackson, but north 

 of it, in a depth of 90 feet, and then have a thickness of at 

 least 325 feet. Hilgard continues: "At Jackson, however, at 

 the Penitentiary well, after passing through 32 feet of surface 

 material and fossiliferous strata of the Jackson age, lignitic 

 clays were penetrated for 418 feet, after which a bed of shells 



