20 () CALCAREOUS JVIAiNUHES— APPENDIX. 



of broken (or water-worn) shells, obviously the same kind dug at anotlier 

 place for manure, and described at page 204, a soft brown sand was reached, 

 apparently destitute ol calcareous matter, and from which rose an abundant 

 supply of pure and soft water to the height, of 13 feet, wiiich stood altoge- 

 ther in this blue marl, without its purity being afiected either by tlie cal- 

 careous matter of tlie marl, or its coloring matter. The continued purity 

 of this water is an additional proof that tlie blue coloring matter is chemi- 

 cally combined with the carbonate of lime — and the combination is a 

 visible illustration of the manner in which marl holds to and fixes putres- 

 cent manures. 



Mr. William Carmichael, of Q,ueen Ann's county, Maryland, an intelligent 

 agriculturist and an experienced and observant marler, is of opinion that 

 there is a perceptible superiority of ellect of blue marls over others of 

 equal (and even greater) strength in calcareous matter. (Farmers' Regis- 

 ter, vol. vii. p. 106.) This superiority of efiect must be caused by the 

 vegetable or other putrescent and alimentary matter being combined with 

 the calcareous, and by its presence giving color to the blue marl. And 

 that the blue color is thus produced is fully proved by the facts stated at 

 page 204, and by my more general observation. 



Excepting then the additional value in the vegetable extract which gives 

 the color, there is no difference between the blue and the yellow marls, 

 other than the difTerence, as of any marls of similar color, in their re- 

 spective amounts of calcareous matter, /.nd the same m"ay be said of wet 

 and dry marls, which are generally, but not always, distinguished by the 

 above colors; and also of any other miocene rriarls, excepting for such 

 proportion of "green-sand" as issometim.es present. But there is reason 

 to believe that wet marls, in many cases, have lost some of their ancient 

 strength, by the continued though very slow percolation and subsequent 

 discharge of water through the mass. If recent rain water penetrates wet 

 marl, it dissolves some carbonate of lime, (by means of the carbonic acid in 

 the rain-water;) and, as the water slowly flows off, or oozes out, instead of 

 being evaporated, the dissolved lime is washed into the nearest stream, and 

 is lost, insteid of being left, crystallized or otherwise, as in dry marl. 

 Again — if water flows over having sulphate of iron (copperas) in solution, 

 (which is not a very rare case,) that dissolved salt acts with the carbonate 

 of lime to produce the decomposition of both the sulphate of iron and the 

 carbonate of lime, and from two of their component parts to form sulphate 

 of lime. And as this is slightly soluble in water, it must be carried olf by 

 the slowly o >zing water, as long as any of these new salts remain. In this 

 case, the carbonic acid is evolved, and the iron is prpcipitated — and often 

 fills, or coats the interior of the spaces before filled by the shells which this 

 chemical process had decomposed and removed. This cfTect, when pro- 

 duced, is seen at the upper part of the marl, where the copperas water first 

 touches the shelly matter. In Henrico, near the western limit of the marl, 

 there is generally over the present highest shells a body of earth of color 

 and general appearance very similar to the marl below, and full of hollow 

 impressions of shells, though no shelly nor even any calcareous matter now 

 remains. Jn other marls, there is often seen an upper layer colored brown 

 by this deposite of iron. Both these are different modes of the same ope- 

 ration; the waters charged with sulphate of iron having in the latter case 

 decomposed and removed but part, and in the former all the calcareous 

 matter, to some depth below the former top of the stratum of marl. 

 The marl, in the upper part of which the shells have been thus dissolved 

 and removed, has a decided sulphureous odor, which is left very perceptible 

 on the hands, after handling the marl as dug; and this odor is still more 



