354 CONTRIBUTIONS TO THE GEOLOGY OF 



(lition of the fossils it contains, merits a description in this place. The 

 strata are follows : 



1. A layer, consisting of common and green sand, the latter in re- 

 markably large grains, and amounting to more than twenty per cent of 

 the whole. A striking feature in this stratum is the immense num- 

 ber of fossils, principally Cytherea ovata (nobis) and Turritella Mortoni, 

 which it contains in the modified condition before described. The 

 shelly matter has almost entirely disappeared, and its place is now 

 occupied by oxide of iron, of a deep brown colour, presenting the most 

 perfect casts, both of the interior and exterior of the shells. This bed 

 contains a notable proportion of green sand, a little mica, and some 

 sulphate of lime and of iron. Its thickness is about eight feet. 



2. A stratum of yellowish white sand, variegated with numerous 

 bright yellow blotches, faintly representing the figures of the shells 

 which they have replaced. These blotches are principally composed 

 of oxide of iron. The chief material of this bed is common siliceous 

 sand, containing a few scattered granules of green sand. Its thickness 

 is about twenty feet. 



3. Diluvium, containing coarse gravel, and some large pebbles. 

 The localities in Staflford, opposite to Fredericksburg, forming one of 



the landmarks of the eocene, above enumerated, are situated near a 

 branch of Claiborne's Run, on a meadow. On Mr Bowen's place a 

 pit has been dug, in which the following strata are exposed : 



1. A bed consisting of green sand mingled with common sand, being 

 the upper layer of the eocene, and, as might be expected, containing 

 no shells. 



2. Two feet of sand and pebbles, mostly of white quartz. 



3. Six feet of yellowish and reddish clay. 



At Dr Wellford's, about one-third of a mile distant from the former, 

 a bed of sand and clay, of six feet thickness, is first penetrated. Be- 

 neath this is found a band of iron sandstone, six inches thick, and im- 

 mediately below this the upper stratum of the eocene. 



At the other points above enumerated, exposures of considerable 

 extent occur, chiefly differing from the foregoing in the larger amount of 

 calcareous matter which they present, and in the usual presence of 

 shell rock in one or more of the strata. At an inconsiderable distance 



