CALCAREOUS MANURES— APPENDIX. 



195 



or the most tenacious clays. The carbonate of lime also tends to preserve an 

 open and mellow textui'e in true marls, disposing the lumps to readily yield 

 and crumble, or fall to powder or to thin flakes, under atmospherical influ- 

 ences, which would only affect clay by making it an intractable sticky mortar 

 when wet, or lumps of almost stony hardness when dry. Moreover, there 

 seems good reason to believe that in true marl there is a chemical combina- 

 tion (and not merely a mixture) of the argillaceous and calcareous ingre- 

 dients, induced by their suspension in water, when the particles of both 

 were in the finest possible state of division, and most intimate intermixture, 

 while so suspended. Besides the crumbling quality just stated, so different 

 from clay, there is a still stronger reason for believing that the calcareous 

 and the silicious parts of true marl are chemically combined, which is, that 

 they cannot be separated by mechanical means, such as agitation and sub- 

 sidence in water. For the suggestion that the different earthy parts of true 

 marl are in a state of chemical combination with each other, I am indebted 

 to the ' Essai sur la Marne,^ of M. Puvis, which work, in an abridged form, 

 I translated and published in the third volume of the Farmers' Register. 

 The author there also states that the marls of France are principally, if not 

 always, of fresh- water formation, as is shown by the shells they contain be- 

 ing either such as belong to rivers and lakes or to the land. This is dif- 

 ferent from any thing known in lower Virginia; all our known marls, whe- 

 ther properly or improperly so termed, being deposites made in a former 

 sea, and the shells being those of sea-animals.* 



But though it is proper to describe that which only is truly "marl," be- 

 fore speaking of what is improperly so called, it is also true that there is 

 nothing to tell of the use of any true marl in Virginia, and scarcely of its 

 existence in the tide-water region. I have as yet seen it in but few places, 

 and then overlying ordinary beds of fossil shells, and intermixed therewith. 

 This marl was thus found in two of my diggings, one on Coggins Point 

 farm and the other at Shellbanks. In both cases, though perfectly charac- 

 terized, the quantity of true marl was too small to be used separately from 

 the more calcareous and much thicker stratum of shell marl below. This 

 true marl was in many horizontal layers, seldom more than an inch in thick- 

 ness, separated by other layers, sometimes very thin, of almost pure shells 



* " It may be of some interest to scientific investigators to know more particularly the 

 shells of these marls of France. In a catalogue annexed to the original ' Essai sur la 

 Marne,' the author names the following shells: 



In a marl sent from St. Trivier — yellowish, compact, of homogeneous appearance, 

 and coming to pieces finely and easily in water — 

 Land shell — Turbo elegans. 

 River shells — Helix fasicuiaris, Helix vivipara, fHelix tentacula, fMya Pictorum. 



In a marl from Cuiseaux, Saone et Loire — 

 River shell — Melanopside (of Lamarck.) 



In a marl from Leugny, in Yonne — 

 Land shell — -fChassilie ridee (of Lamarck, and Draparnaud,) fHelix lubrica. 



In a marl from St. Priest in Dauphlny — earthy, yellowish, very easy to crumble in 

 water — 

 Land shell — f Ambrette alongee (of Lamarck and Draparnaud, *Helix hispida. 



In an analogous formation of marl, in the basin of the Rhone, beween Meximieux 

 and Montluel, the Helix striee, a land species is found in great abundance." 



M. Puvis states that among these, and among all the species of shells found in the 

 marls of the basins of the three great rivers, Saone, Rhone and Yonne, there are no 

 remains of sea shells. All seem to have been formed under fresh water. " But (he 

 continues) as these marls contain land shells, olten in great abundance, we must con- 

 clude, that the revolution which heaped up the marls, has been preceded by a time in 

 which the land was not covered by water, in which the earth producing vegetables, 

 permitted the multiplication of the species of land shells which were found in these 

 marls." — Essai sur la Marne, p. 8 to p. 24, and translation in Farmer's Register, iii., 

 note to p. 692. 



t Living species are still found in the same region similar to those marked thus. 



