CALCAREOUS MANURES— APPENDIX. jgg 



to small fragments, and which also left, in shaping the surface of the marl, 

 the marks of whirl-pools or other violent disturbance. From such sup- 

 posed causes might be expected such eifects as many of the various marl- 

 beds actually exhibit. In different places, and sometimes in the same 

 place, the shells and their fragments are found of all sizes, and of all condi- 

 tions of preservation ; and intermixed, in various proportions, with such 

 clay, or fine sand, as might be suspended in or borne by currents ; so as to 

 form beds of every degree of texture and shade of color. The shells, and 

 their fragments, or the carbonate of lime, are in various proportions of quan- 

 tity, from 10 per cent., (or even less in rare cases,) to 90 per cent, or more, 

 of the mixture, or whole mass. In different beds, and sometimes in conti- 

 guous layers of the same bed, the shells are in every state of preservation 

 or of decay ; from that of being firm, and often entire in their calcareous 

 structure, and the most delicate parts of their beautiful forms preserved, to 

 that of being mostly broken down, and almost reduced to a coarse powder, 

 and sometimes even forming a homogeneous mass of still finer particles 

 in which the forms of but few if any shells are distinguishable. The ori- 

 ginal bright and various colors of the shells are lost, and they are nearly 

 all white — a few of the hardest only being brown or gray. The texture of 

 the mass also varies, from a loose sand to a firm body of almost stony 

 hardness. The earth intermixed with the shells is generally much more 

 sandy than clayey, and more especially in the poorer marls. Even when 

 the admixture of earth is clay, it rarely makes the marl appear the least 

 clayey in texture, or plastic or adhesive, because the clay is but in small 

 proportion to the shelly matter. The color of the miocene marls is also 

 various— generally either pale yellow or dingy white or blue, sometimes 

 bright, but more often a dull blue, or ash color. The richest marls, of 

 homogeneous texture, are nearly white when dry, and approach in appear- 

 ance to a coarse or impure chalk. There is no true chalk known to exist 

 in this country. 



The shell marls of Virginia are confined almost entirely to the tide- water 

 region, or the space eastward of the granite which forms the falls of all 

 our eastern rivers. But near Petersburg (on the farm of Dr. William J. 

 Dupuy, and other adjoining lands,) there is an exception to this general 

 rule, the marl being found about a mile farther west, over-lapping the 

 eastern part of the granite, and passing under a small stream which emp- 

 ties into the Appomattox, a mile above the lowest falls. A thick stratum 

 has also recently been found in Richmond, above the Penitentiary, and of 

 course above the lower falls of James river. 



The only important fertilizing ingredient of the miocene marls is the 

 carbonate of lime, or shelly matter. There may be, and probably is, some 

 slight additional benefit sometimes, by accidental or peculiar admixtures 

 of other substances ; as, of animal matter still remaining, or of vegetable 

 extract in blue marls, of the oxide of iron, of a small proportion of green- 

 sand generally, and even of the clay or the sand respectively for soils de- 

 ficient in either. But either and all of these additional matters, though 

 giving some value as manure, are of but little importance in miocene marls, 

 in comparison to the main and great agent of fertilization, the shelly or 

 calcareous matter. According then to the greater or less proportion of 

 this main ingredient, and to its state of division or readiness to be reduced 

 to a state of minute division in the soil, may be rated the comparative values 

 of marls for manure. In regard to the much larger proportions of green- 

 sand in miocene marls, as asserted by other authority, some additional re- 

 marks will be hereafter submitted, in the proper order for consideration. 



As might be inferred from the obvious manner of the deposition of the 

 marl, as before stated, by waters of the sea in violent and yet varying 



