CALCAREOUS MANURES— APPENDIX. £01 



the rich marls in and about Williamsburg, and in Surry and that belt of 

 country generally, containing 70 to 80 per cent, of carbonate of lime. 



The different varieties of miocene marls which will now be more par- 

 ticularly described are not always separated in different beds, but some- 

 times form some of the different and even adjoining layers of the same 

 bed or digging. The differences of color, &c., caused by the greater or 

 less quantity of various accidental ingredients, however striking to the eye, 

 are not often of much importance to the value of the marl ; hut only 

 (or principally) such differences as are caused by the greater or less pro- 

 portion of shelly matter, and its state of disintegration and division. 



(a) Yelloiv marl.— This kind, wherever found, always forms the highest 

 layers of the particular body. That is, if there be layers both of yellow 

 and blue marl in the same body, the yellow is always above and the blue 

 below, and never in the reverse position. But sometimes the yellow con- 

 tinues to the bottom, and sometimes the blue forms the top as well as the 

 bottom. 



Yellow marl is usually found dry ; that is, having no springs or oozing 

 waters, which are generally reached on digging lower in the body. But 

 the lower part, where wet, is sometimes, though rarely, of the same yellow- 

 ish or dingy white tint, so as to make it manifest that the color is not de- 

 pendent on the degree of moisture or dryness. The yellowish tint is 

 owing to the presence of oxide of iron, and is pale or deep, approaching 

 sometimes to reddish brown, according to the quantity of that coloring 

 matter. 



Yellotv sandy marl is the kind most abundant in Prince George county 

 on and at some miles distance from the banks of James river, and from 

 which some farms entirely, and others principally, in that neighborhood 

 have been marled. It is of shells left in their original place, the filling 

 earth being mostly of coarse sand, and the whole body poor in calcareous 

 matter, varying in its proportion usually from 20 to 30 per cent, and rarely 

 richer than 35 per cent. But it is of such open and loose texture, (and 

 the more so as the sand is the more abundant,) that this marl is easily and 

 cheaply worked, and the labor so applied is therefore often better compen- 

 sated than in diggings of much richer marl. In this variety of marl, the 

 shells are usually entire, or in large fragments, but are not firm or well 

 preserved. In some beds, or thick layers, they are so finely reduced that 

 the mass seems to the eye to be wholly, as it is indeed principally, a body 

 of silicious sand. From one bed of this kind which its proprietor supposed 

 from its appearance to be merely silicious, it was used as sand to mix in 

 lime mortar for masonry, and it was found to serve well for that purpose. 

 Subsequently this bed of sand was found to be enough calcareous to be 

 used as manure; and was so used, and to such good profit, that the proprie- 

 tor supposed it to be rich marl. In that opinion, however, he was mistaken, 

 at least as to the calcareous contents. 



Yellow clay marl.— But most of the richest as well as of the poorest 

 miocene marls are yellowish. When rich, say containing proportions of 

 carbonate of lime from 45 to 80 per cent,, the marl is usually formed of 

 shells broken down, when under the sea, to small fragments or to powder, 

 by the grinding action of the water in violent motion, and left afterwards to 

 settle in stiller water, according to the specific gravity. Or it is the same kind 

 of rich and finely divided water-borne matter deposited on and filling the hol- 

 lows in and between whole shells remaining in their original place. In either 

 case, the small quantity of earth first suspended in the current, and then de- 

 posited with the finely reduced shelly matter, is mostly if not entirely clay; 

 as silicious sand, having more specific weight, could not be suspended by 



