LYELL ON THE MIOCENE BEDS OF N. AMERICA. 415 



them resting on eocene deposits, or on sand and clay containing an 

 assemblage of shells resembling those of the London and Paris 

 basins. 



2dly. The genera of shells, and the amount of species by which 

 they are represented, agree for the most part with those which 

 characterise the European miocene beds. Many of the most abun- 

 dant species are allied, and some few are identical. 



3dly. The proportion of fossil shells identified with recent 

 species amounts to about 17 per cent, or about one-sixth of the 

 whole, in 147 species collected by me, the recent species agreeing 

 almost entirely with those now living in the neighbouring parts of 

 the Atlantic. 



4thly. There is the same mixture of shells of northern and 

 southern forms as in the French faluns. 



5thly. Of ten species of corals, all but one agree generically 

 with those of the miocene beds of Europe, and two at least speci- 

 fically. One of these is a Lunulite, the same as a fossil from the 

 Suffolk crag and also from the faluns of Touraine ; a second, An- 

 thophyllum lineatum, is also common in the French faluns. 



6thly. Among the remains of fish are several of the shark family, 

 agreeing with species from the miocene beds of Europe, the faluns 

 of Touraine, the molasse of Switzerland, and the tertiary formation 

 of Malta, among which I may mention Carcharias megalodon, 

 C. productus, Lamna xiphodon, L. hastalis, L. cuspidata. The 

 ossicles also of the ears of fishes closely resemble those occurring 

 in the Suffolk crag. 



7thly. The absence of reptiles is another point of analogy, as 

 also the presence of huge cetaceous remains. 



The miocene deposits of the United States consist chiefly of in- 

 coherent sand and clay, and in this respect bear a strong resem- 

 blance to those of the same age in Europe. The associated 

 siliceous sand imparts a sterile character to the space they occupy, 

 but the soil has often been fertilised by the use of shell marl, 

 derived by the agriculturist from parts of the same formation, a 

 practice which Mr. Ruffin, of Petersburg, Virginia, editor of the 

 Farmer's Register, has done much to promote. This use of the 

 miocene marl and fossil shells affords another singular point of 

 coincidence between the American strata, the English crag, and 

 the faluns of the Loire, all of which furnish the same fertilising 

 calcareous materials for improving light soils. 



I began my examination of these middle tertiary deposits in the 

 suburbs of Richmond, Virginia, where I saw in Shockoe Creek 

 red clay and sand, from which I obtained Artemis acetabulum, and 

 casts of miocene species of Astarte and Mactra, reposing on 

 eocene marls with characteristic shells. Between the two forma- 

 tions, a remarkable bed of whitish and yellowish siliceous clay 

 intervenes, from twelve to twenty-five feet thick, of an extremely 

 fine texture. It affords a very sterile soil, and its course through 

 the country is marked on the surface by a band of meagre vegeta- 

 tion, without trees or shrubs. It has been described by Professor 



F F 2 



