CALCAREOUS MANURES-PRACTICE. 25 j 



present before it will be dug for manure. From all the scattered evidences 

 of the presence of this deposite, it may be inferred that it lies beneath 

 nearly every part of our country between the sea and the granite ridge 

 which forms the falls of all our rivers. It is exposed where it rises, and 

 where cut through by the deep ravines of hilly land and by the courses of 

 rivers — and concealed by its dips, and the usual level surface of the coun- 

 try. The rich tracts of neutral soil on James river, such as Shirley, West- 

 over, Brandon, and Sandy Point, seem to have been formed by alluvion, 

 which may be termed recent compared to that of our district in general ; 

 and in these no marl has been found, though it is generally abundant in 

 the adjacent higher lands. Fresh-water muscle shells are sometimes found 

 in thin layers, (from a few inches to two feet thick,) both on these lands and 

 others— but generally near the surface, and always far above the deposite 

 of sea shells, found under the high land. These two layers of different 

 kinds of shells are separated by a thickness of many feet of earth, contain- 

 ing no shells of any kind. Muscle shells are richer than the others, as 

 they contain much gelatinous and enriching animal matter. On this ac- 

 count, the earth with which muscle shells are found mixed is a rich black 

 mould. Most persons consider these beds of muscle shells as artificially 

 formed by the Indians, who are supposed to have collected the muscles for 

 food, and left the shells Vv'here the fish were consumed. There are some 

 strong reasons which may be adduced both to sustain and to oppose this 

 opinion. But whatever may be the origin oT these collections of muscle 

 shells, it does not affect their qualities as manure for the soils in which 

 they are found, or for others to which they may be removed. 



Neither the fossil sea shells, nor the earth mixed with them, are supposed 

 to contain any important or considerable proportion of putrescent matter 

 — and this manure has been considered thi'oughout this essay as being 

 valuable only as containing calcareous earth. This, no doubt, is the only 

 ingredient of any worth, in the great majority of cases. But sometimes 

 there are other ingredients— which must be considered merely as excep- 

 tions to the general rule. One of these exceptions has already been stated, 

 in the descrl^Dtion of gypseous marl, (page 92 ;) and some others have be^n 

 discovered since the publication of that statement. A kind of earth, contain- 

 ing a large proportion of carbonate of magnesia, as well as of carbonate 

 nate of lime, has been found in Hanover county, Va. {Farmers'' liegister, 

 vol. i.) Professor Rogers, of William and Mary College, has discovered, in 

 many of the marls of lower Virginia, some proportion of the " green 

 sand" of geologists, or what is itself called " marl," (another misapplication 

 of that name,) in New Jersey, and which has there been found highly va- 

 luable as manure, though containing not a particle of the carbonate of liine, 

 which constitutes the sole value of shells and calcareous manures in gene- 

 ral. The formation or body of this green-sand, separate and distinct from 

 any marl, I had discovered long before, and of which a full account will be 

 given in a subsequent pait of this essay. But however interesting may be 

 the discovery of these different ingredients of particular bodies of marl, 

 and however valuable they may prove as manures, still they are not to be 

 considered as treated of in this essay under any general observaliims on 

 marl — which observations are dosigued to be applied simjily to iiianure of 

 which the only useful ingredient is the carbonate of lime. 



More than a hundred kinds of sea shells are found in the beds of marl, 

 that I have worked, without counting any of very small size. Many kinds 

 would escape common observation., and others wuuld re((uire the aid of a 

 magnifying glass to be distinguished. Generally the shells, though fragile, 

 are entire, but are much broken by the digging,: and after -opei-ations. The 



