CALCAREOUS MANURES— APPENDIX. £29 



those of the oyster kind. Below this stratum, the marl '^as shown by the 

 sample) has no shells or considerable fragments, is of dark jiray color and 

 homogeneous texture, like coarse sand united in a mass by barely enough 

 of clay to serve for that purpose. This apparent texture belongs to most 

 of the Pamunkey marls, and is caused by the shelly matter being so pul- 

 verized as to be in fact a coarse calcareous sand. The specimen of this 

 lower stratum, of which 8 or 10 feet depth had been exposed, contained in 

 100 grains, 35.50 of carbonate of lime; and the upper (shelly stratum) 35. 

 The green-sand in both kinds appeared to be in less proportion than in the 

 marl of the river bank at Northbury, and elsewhere along the river 

 generally. Probably there was not more than 20 per cent, at most. The 

 upper stratum, and larger part as used, of this marl, through a line of 

 several miles in length, is very different in appearance from all the other 

 marls seen on the river. And it must also be different in geological age or 

 manner of original deposition, as the shells show much difference. Very 

 few of the cardita plam'costa were found in the heaps of marl, (which al- 

 ways offer the best exhibition of shells for collection,) and those of very 

 small size, and no saddle oysters. On the other hand, several shells were 

 found, not observed by me at any other place ; and one of them, an oyster 

 shell of large size, of remarkable and peculiar form, and in excellent pre- 

 servation, is very abundant. Though various in form, as are all the ostreas, 

 this, or the more convex of its two valves, has a general peculiarity in a 

 large and sharp hump on the back, and sometimes two such humps. Ano- 

 ther ostrea, of which the shell is very tiiin and very convex, and the out- 

 line of the valves nearly circular, is here abundant, and as large as two 

 inches across. No specimen of the same had ever been seen by me, ex- 

 cept perhaps a few at Newcastle of size so small that the identity was 

 doubtful. The striking differences of kind and of proportions of the shells 

 at Mr. Webb's more recent diggings would be highly interesting to any 

 person possessing that knowledge of geology, and its auxiliary science, fossil 

 conchology, to which I have no claim, and make no pretension. I have 

 done, however, all in my power, to increase the facilities of future com- 

 petent investigators, by collecting and preserving specimens for their 

 examination. My cabinet contains not only some of all the shells that I 

 have found, or have been able to obtain from the several kinds of marl, but 

 also specimens of all the marls of peculiar and marked character, with their 

 localities accurately distinguished. And the time and the labor which 

 I have given to making the collection, with opportunities possessed by but 

 few other individuals, may thus serve greatly to advance the pursuits of 

 scientific and truly competent investigators. 



In the river bank of Mr. Carter Braxton's farm, immediately above the 

 Newcastle ferry, there commences a rapid decrease of the thickness of the 

 calcareous or marl stratum proper, which is substituted by an equal in- 

 crease or rising of the under-lying green-sand earth. A little above the 

 ferry, the marl is at least 10 feet thick; at less than a mile above, the thick- 

 ness of the marl is only 5 feet ; and at the next large exposure, on the 

 adjacent farm of Mr. B. Tomiin, the marl is not more than 2 or 3 feet 

 thick, over-lying green-sand earth marked with a few scattered and small 

 shells, rising to nearly the full usual height of the marl, say 25 feet or more 

 visible above the water. This was as far in regular connexion along the 

 river as I personally examined ; but I learned that still higher, the calca- 

 reous stratum almost ceases, the lower stratum of green-sand earth occupy- 

 ing nearly the whole visible section. The lower stratum of the body at 

 Spring Garden, Hanover, (Mr. Wilham H. Roane's farm,) next above, is 

 stated in Professor Rogers' Report as containing, in 100 parts — 



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