CALCAKEOUS MANURES-APPENDIX. 207 



manifest in the marl when it has been dug and thrown out, and exposed 

 some days to the weather. Such marl is within a few miles of Richmond, 

 at Dr. Chamberlayne's and Col. C. W. Gooch's farms. It is poor in calca- 

 reous matter. 



The comparative values of marls are fixed by the comparative propor- 

 tions of carbonate of lime contained, other circumstances being alike; yet 

 if these circumstances are very different, they may make a marl containing 

 ■ but 25 per cent, worth more than another of 50 per cent. Tlie more finely 

 reduced, or the more rotten the shells, the quicker the action will be, and 

 the more profitable the marling. But all the white shells, however hard and 

 entire when applied, are dissolved in a k\v years, if the soil really needs so 

 much lime — that is, (according to my views,) if there be acid of soil enough 

 to combine with the lime. But the brown or slate-colored shells seem to 

 be insoluble and almost indestructible, and do very little good as manure. 

 These shells are the several species of scallop (pecten) and of fossil oyster, 

 ipstrea,) and some iew others, all fortunately being but in small proportion 

 to the numerous white and softer shells.' Some beds of marl, however, or 

 layers, have mostly these hard shells, and therefore are worth very little 

 compared to what their chemical analysis would indicate. 



A list of most of the shells found in the miocene marls, and also of the 

 eocene of Virginia, (and of which specimens are in my collection,) will be 

 aniiexed to this article, for which I am indebted to the scientific knowledge 

 and kind assistance of Mr. M. Tuomey. But as the scientific names will 

 be of but little use to many readers, it may be useful to describe in ad- 

 vance a few of the most common shells, peculiar to the miocene marls, and 

 which can scarcely be mistaken. Such are the various large scallop shells, 

 {pecten,) oysters, (ostrea Virginica, S,-c.) — hollow tubes, about the thickness 

 of a large pipe-stem, and open at both ends, (serpula,) and eliptical funnel- 

 shaped shells having a small hole at the bottom, (Jissurella.) These refer- 

 ences will be enough for any person acquainted with the shells by sight, but 

 not acquainted with their scientific names. If however even very slightly 

 informed in the latter respect, the observer will not need any such expla- 

 nations. 



It is not necessary to speak otherwise than very concisely as to the 

 practical applications and effects of miocene shell marl ; for this is the kind 

 in general use throughout lower Viiginia and Maryland and to such small 

 extent as has been used in North Carolina, and therefore ihe operation is 

 well known. All the usual and general and highly beneficial effects of 

 marl known, with but few exceptions in the limited districts of eocene 

 marl, (hereafter to be described,) are due to the miocene marls. And of 

 such effects, there have been numerous statements, general and particular. 

 The operation of the eocene marls, and especially those largely mixed 

 with "green-sand," is different, and superior; but their use has been so 

 limited, and so few statements of effects published, that nearly all the 

 particular results and general statements of effects yet laid before the 

 public, in the ' Essay on Calcareous Manures' or elsewhere, have been in 

 relation to the miocene marls. 



EOCENE MARL. 



(c) — Calcareous marl, containing but little green-sand. — The existence 

 in Virginia of the marl now known as eocene, was first discovered 

 in 1819 by myself in the south bank of James river, underlying the pro- 

 montory of Coggins Point; and in the same year it was tried as ma- 

 nure. The texture and general appearance of this marl were obvious- 



