THE LOESS OF NACHEZ, MISS. 303 



mining of the underlying sands and gravels it would long resist 

 the action of air and water. Along the N. O. & N. W. R. R., 

 in the cut near the depot, (exposure 1 on the map), the very 

 steep sides still retained the marks of pick and shovel at the 

 time that the photograph reproduced in Plate IV. was taken, 

 though the excavation had been made about seven years 

 before. 



This similarity of the Natchez loess and that of the Mis- 

 souri river bluffs in all excepting fossils suggests the probable 

 source of much, if not all, of the material which composes it. 



The fossils are the most interesting feature of the southern 

 loess. Here, as elsewhere, the characteristic fauna is mollus- 

 can, but differs in many respects from that of the northern 

 loess. Notwithstanding the fact that the fossils formed the 

 special object of the writer's investigations, there were found 

 among them no species which are aquatic, or in any sense 

 even "semi-aquatic." Not even those forms which belong to 

 the fauna of the small pond and shallow stream, and which 

 sometimes occur in northern loess, were found here. Singu- 

 larly, too, such species are quite absent from the modern fauna 

 of the uplands in and about Natchez, for there are no springs, 

 or ponds, or swampy areas in which such snails as Physa, 

 Limn&a, etc., might thrive. It is true that aquatic species 

 have been reported from this loess, but in all cases the reports 

 are either indefinite, or refer to that which may not be loess. 



As early as 1846, Lyell* noted a deposit at Natchez resemb- 

 ling loess and with "land, fluviatile and lacustrine shells of 

 species still inhabiting the same country," but he did not 

 designate them by name. Later, discussing the loess of Nat- 

 chez in the London Times t he said that the deposit "contains 

 abundance of fresh water and land shells, of which I myself 

 obtained more than 20 species .... They belong to the 

 genera Helix, Hcliciiia, Pupa and Succinea, accompanied or 

 rather replaced in a few places where the loam passes into 

 shell-marl by Lymuca, Planorbis, P/iysa, Cylas .... All 



* Athenaeum, Sept., 1846. 



tDec. 8, 1846; reprinted in the Am. Jour. Sci. and Arts, 2nd series, 

 vol. Ill, pp. 267-269, 1847. 



