38' FOURTH REPORT — 1834. 



rolina. Throughout this great area it has scarcely received any- 

 geological examination, our only accurate information being 

 that procured by Conrad in his researches among the fossils in 

 Suffolk county, and again at York town, and some recent exa- 

 minations made by my brother, W. B. Rogers, along the James 

 and York rivers and the peninsula embraced between them. The 

 general distribution of the formation, however, is well known, 

 because the fossiliferous parts of the deposit are soxight over 

 nearly the whole region for the fertilizing action of their carbo- 

 nate of lime and shells upon the soil, in consequence of which 

 the whole deposit bears the name of marl in all the States in 

 Avhich it occurs. I select for description the beds upon the 

 James and York rivers, as being best known to us, and probably 

 characteristic of the deposit generally. 



On the James river, along the cliffs in the counties of James 

 city and Warwick, the fossiliferous strata are finely exposed. 

 My brother. Professor Rogers, thus describes the locality : " By 

 far the most striking exhibition of the tertiary strata which I 

 have yet seen is on the bank of James river, from a little above 

 King's Mill upwards. The bank has an average height of sixty 

 feet, and from the water-line to a few feet from the top is occu- 

 pied by shells : in some places huge blocks of the deposit have 

 fallen down, exposing the specimens in a very perfect state. The 

 mass in which the shells are imbedded is usually a stratum of 

 sand, sometimes covered by, but mostly resting upon, blueish 

 clay, which also includes the same fossils. The sand, as in 

 Maryland, is mostly yellowish, though it has often a green hue, 

 like that called turtia by the French. It is sometimes indu- 

 rated into a rough concreted mass by the cementing action of the 

 carbonate of lime of the shells. An interesting fact is, the oc- 

 currence among it of the green grains so chai'acteristic of the 

 secondary greensand of New Jersey." 



My brother states, that after examining at least thirty distinct 

 localities, he has found the greensand an invariable ingredient 

 in all, some having as much as thirty per cent, of this mineral. 

 At Burwell's Mill the stratum over the shells for five feet is an 

 olive and red clay, containing from thirty to forty per cent, of 

 the greensand, from which it receives its colour, olive or green, 

 precisely as certain beds of similar clay in the secondary tracts 

 of New Jersey acquire the same tint. 



A section upon the side of a mill-pond recently drained near 

 Williamsburgh, about midway between the York and James 

 rivers, affords the following arrangement: 1st, reddish sand, 

 about eight feet, containing near the bottom a stratum two feet 

 thick of shells, chiefly Fenus and Area idonea, very large : 



