62 



from fish. Along with these are innumerable casts of Eocene 

 shells, Carditas, Turritellas, Crassitellas, Cythereas, &c. Where 

 it adjoins the subjacent mottled stratum the transition is marked 

 by a thin ferruginous band crowded with impressions of Turri- 

 tella, &c., which are deeply stained with oxide of iron. This sub- 

 division, where thickest, has a depth of about twelve feet. 



3. Resting upon the dark stratum just described is a second 

 arenaceous bed of a light yellowish tint mottled with brown and 

 varied by thin ferruginous layers. This also contains numerous 

 impressions of shells. Some distance up the ravine it exhibits a 

 thickness of about eight feet, but is seen irregularly thinning out 

 toward the lower end of the hollow, where its upper surface 

 bears marks of irregular denudation prior to the deposition of the 

 overlying Meiocene deposits. 



4. At the base of the Meiocene strata we find a thin bed of 

 whitish and sometimes ochreous clay mingling towards the top 

 with the lighter material of the Infusorial stratum, which here 

 attains a thickness of from twenty to thirty feet. It is this local- 

 ity that twenty years ago furnished Prof. Rogers the first speci- 

 mens of Tertiary Infusorial earth discovered in the United States, 

 and led him to the recognition of a similar deposit in the Tertiary 

 of other localities in Virginia and Maryland, which, like that of 

 Richmond, have since become so familiarly known to microscopic 

 observers in all parts of the world. 



5. Above the Infusorial stratum, here forming a bench often 

 denuded and in such cases conspicuous from its whiteness, we 

 find a series of strata consisting of various intermixtures of clay 

 and sand, of which the lowest is usually a compact, light colored 

 clay, the next a bluish or grayish, more arenaceous mass, and 

 the uppermost an argillaceous stratum of a light brown and 

 mottled appearance. The highest of these Meiocene strata is 

 overlaid by a deposit of coarse gravel such as forms the usual 

 superficial material of this region in the vicinity of the large 

 rivers. The thickness of that part of the Meiocene which lies 

 between the Infusorial stratum and this surface deposit, amounts, 

 in the neighborhood of the present section, to about twenty-five 

 feet, but at other points where less reduced by denudation it dis- 

 plays a considerably greater mass. Throughout most of these 

 beds the casts of well-known Meiocene fossils are of very frequent 



