204 CALCAREOUS MANURES-APPENDIX. 



down the country, it sometimes forms the whole of low-lying beds, but 

 more usually only the lower layers of a bed, of which the upper part is 

 yellow. 



Blue marl is generally such as remains "in place," or where the shells 

 were left by the death of the enclosed animals, and the intermixed earth 

 is mostly siliclous sand ; and therefore, (and not because of its color,) this 

 marl is rarely found as rich as 45 per cent., and is still more rarely equal to 

 the yellow clay marls, though generally richer than the yellow sandy marls. 

 Blue marl in the bed is always wet, being made so by water slowly 

 oozing from every part, though seldom fast any where, or showing springs 

 or veins of running water. The blue color is not caused by moisture, (for 

 some yellow marls are also permanently wet,) but by vegetable extract, or 

 other dark-colored putrescent matter, brought in the percolating water. 

 This inference I have drawn from extensive observation of the natural 

 beds, and also from several accurate though accidental experiments, of 

 which the first that was observed will be here stated. A small stable 

 yard was covered 6 to 10 inches thick with a rich dry yellow marl, for the 

 purpose of retaining by chemical combination the juices of the putrescent 

 manure which was to be thrown there from the stable. After remaining 

 for this use a year or more, this flooring of marl was dug up and carried 

 out for manure; when it was found to be changed in color to a deep and 

 vivid blue, and precisely like the natural color and appearance of the under- 

 stratum of the same body of marl, which being an open and almost pure 

 mass of pulverized (and water-borne) fragments of shells, was readily pene- 

 trated by and always full of water. A general fact confirming this view 

 is that all marls found lying immediately under swampy soils, full of vege- 

 table matter, are blue. And this coloring vegetable matter in marl is not 

 merely intermixed with, but must be held in chemical combination by the 

 calcareous matter ; and serves, according to its quantity, in blue marls, as 

 an an addition to the fertilizing power of the calcareous matter alone. The 

 particular body of marl above referred to, the under-stratum of which is 

 the most marked or vivid blue ever seen in marl, is at Shellbanks farm, 

 Prince George, and from which I dug and applied a large quantity. The 

 greater part, and all the richest layers seemed to be of shells broken down 

 to a coarse powder, or of sizes less than fine gravel, through which clear 

 water rose and passed so freely as to forbid diL'ging to the bottom. The 

 small quantity of clay or other earth intermixed with the calcareous earth 

 of this marl is altogether insufficient to hold so much coloring matter; and, 

 moreover, if the coloring matter were not chemically combined with the 

 calcareous, the continued free passage of water must have dissolved and 

 washed off any uncombined vegetable extract. This whole body of marl, 

 both the dry and yellow lying at top, as well as the blue and wet below, 

 was all brought and deposited by currents, as is manifest by the different 

 layers of different specific gravity, and still more by the many intervening 

 layers of a fine calcareous clay, (before mentioned,) which may be consi- 

 dered as the true marl of mineralogists, though in very small quantity. Ana- 

 lyses were carefully made of every different quality, and the results may be 

 interesting as showing how much one layer may vary from the one next 

 adjoining ; and different specimens not more than a few inches apart. 

 Upper dry part, yellow, and loose as sand, varying (by unevenness of sur- 

 face) from 3 to 7 feet, contained of carbonate of lime - 53 per cent. 

 Next layer below, brownish yellow, through which water 



passes, - - - - - - - 25 " 



About 12 inches lower, in the blue, - - - 64 " 



" " " " " another specimen below 69 " 



Layers of clay marl, interspersed through the above - 9 " 



