142 GEOLOGICAL HEPOKT. [1220 



Within the bed or series of beds, here marked as No. 5, the thickness of the 

 several ledges vaiies greatly, so that detailed sections taken at different points of 

 the bluff, exhibit notable variations in this respect. There are, however, several 

 horizons which may be recognized almost everywhere, if the land slides which 

 have taken place at many points, be left out of consideration. Thus, about 25 to 

 28 feet above bed No. 4 (containing the large oysters), we find a succession of 

 4 to 5 narrow bands (each 8 to 15 inches thick) of marl and laminated clay, 

 which may be identified at all points, and acquire some importance from the 

 circumstance that immediately beneath them, for the next 10 to 12 feet, the 

 purest and hardest limestone (from whose strata most of the building stones 

 and flagstones used at Vicksburg have been quarried) is found. The specimen 

 of limestone analyzed (^305) was taken from a point about 5 feet below the 

 clay seams in question ; while the marl (U278) is derived from the 4 foot 

 stratum immediately overlying the clay bands. Another stratum which, from 

 the abundance and character of its shells, may be recognized easily, lies about 

 16 feet above the clay bands — a reddish, sandy marl, about 3 feet thick. Its 

 shells are white, well preserved and easily washed out by the rains ; among 

 them, Ostrea Viclisburgensis, Area Mississippiensis, Cardium diversum, Den- 

 talium Miss., and numerous species of Pleurotoma, are conspicuous. Immediate- 

 ly beneath it lies a 3 foot bed of semi-indurate marl with large nodular masses 

 of limestone, which can also be identified at most points ; and the whole 

 character of the strata from this bed upwards to the Orange Sand, shows a close 

 correspondence with No. 6 of the Brandon section (Sec. 30, TT218). 



The various clayey strata and bands of the exposure (from which to the marl 

 there are many insensible transitions) give rise to patches of "prairie soil" on 

 the Vicksburg hills. — At some of the higher points where deep washes have 

 exposed the formation, we find at the base of the Orange Sand or its representa- 

 tives, blue sandy clays greatly resembling some of those of the Grand Gulf 

 Group. 



FOSSILS OF THE VICKSBURG GROUP. 



(Mostly occurring at the Vicksburg bluff). 



FISH. 



Carcharodoii angustidens, Ag. Saurocephalus lanciformis, Haul. 



Carcliarodon megalodon, Ag. ? (may Otolithes. 



belong only to the Jackson Group.) Ichtyodorulites, scales and other remains 

 (udeocerdo latidens, Ag. of fish. (Waii.es). 



Teeth of several other species of 



Bqualideae. 



CRUSTACEA. 



In the limestone of Vicksburg Marshal)' and Stewart's quarries, and Brandon 

 iborhood, the plates, claws, etc., of a short-tailed crab are quite abundant. 



[T. A. Co . Sc. of PI 

 Ac. Oct. 1847.] 



BIVALVES. 



Panopaea oblongc Tellina Vicksburgen 



Pholas triquetra. Donax funerata. 



Amphidesma Missis.' i ( h/llierea aslartiforu, ' . 



Psammobia papyria. I tytherea imitabilis. 



Psammobia lintea. Cytherea semi-punctt 



Tellina pecU erea Miss. 



Tellina sci sobrina. 



