1845.] 551 



deserted village of Jamestown, and seven miles south of Williams- 

 burg, Virginia, a range of cliff about forty feet high, in which green- 

 ish and yellowish sandy marls of the miocene formation are well 

 exposed. At the top of the cliff is a bed of red earth, without fos- 

 sils, about ten feet thick. Below this is a layer of shells almost 

 entii'ely composed of Chmna congregata, both valves in each in- 

 dividual being usually found united. Below is a mass of shells 

 about twelve feet thick, consisting almost entirely of the genus 

 Pecten, but associated with others, of which the Astarte undulata 

 before mentioned is the most abundant. The Pectens are closely 

 packed together, with only a slight quantity of accompanying 

 earth. A geologist who should merely collect the shells which 

 have fallen in great numbers on the beach would imagine that 

 bivalves preponderate, to the exclusion of univalves, which, how- 

 ever, is not the case. The univalves are more readily destroyed 

 by frost, I'ain, and the sun, and have therefore disappeared after 

 exposure, but on digging into a fresh stratum, I met with shells 

 of the genera Conus, Oliva, Marginella, Fusus, Pyrula, Murex, 

 Natica, and others. I found no admixture of freshwater or land 

 shells here or in any other locality. 



At Burwell's Mill, near Williamsburg, I found a bed of marl 

 about twelve feet thick, very rich in shells, so that I collected 

 there more than seventy species, besides seven species of corals, 

 mingled confusedly with the shells, in which last there appeared 

 to be no order of arrangement, except that in one part, near the 

 top, the Chama congregata, accompanied with a Fissurella, and a 

 few others, predominated greatly. Among other signs of the slow 

 accumulation of this mass of sandy marl and shells, I may mention 

 that full-grown barnacles and corals are attached to several of the 

 Pectens and other large shells. About one in five of the species 

 of moUusca procui-ed from this marl pit are not distinguishable 

 from those now living in the neighbouring sea. 



That remarkable variety of miocene marl which is of a bluish 

 green colour, and which I have mentioned as occurring near 

 Coggin's Point, is well exhibited in a valley near the town of 

 Petersbui'g, Virginia, where it is used for fertilising the land. It 

 rests on eocene strata, also containing green earth, but of a darker 

 colour. The blue miocene marl is about sixteen feet thick, rich in 

 shells, and is covered by yellow sand, and mottled red and grey 

 clay, about fifty feet thick, with many other sandy strata still 

 higher in the series, which may be observed near the summits of 

 the hills boi'dering the valley. 



All the miocene strata of the James River are horizontal, but 

 the vipper surface has been denuded very unevenly, and often with 

 a deeply indented outline, after which the whole country has been 

 reduced to one level by the deposition of an incumbent mass, con- 

 sisting chiefly of red clay. The great Avidth of .estuaries such as 

 that of the James and other rivers which have narrow channels in 

 the higher and mountainous region, may probably be attributed 



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