CALCAREOUS MANURES— THEORY. 5] 



No. 2. — 1000 grains yielded 5 of coarse, 



2 finely divided. 



7 

 No. 3. — 1500 grains yielded 15 of coarse, 



2i finely divided. 



17 



The specimens. No. 1 and No. 2, were obtained by taking handfuls of soil 

 from several places, (four in one case, and twelve in the other,) mixing them 

 well together, and then taking the samples for trial from the two parcels. 

 On such land, when not recently ploughed, there will always be an over 

 proportion of the pieces of shells on the surface, as the rains have settled 

 the fine soil, and left exposed the coarser matters. On this account, in 

 making these two selections, the upper half-inch was first thrown aside, and 

 the handful dug from below. No. 3 was taken from a spot showing a full 

 average thickness of shells, and included the surface. 1 considered the 

 three trials made as fairly as possible, to give a general average. Small as 

 is the proportion of finely divided calcareous earth exhibited, it must have 

 been increased by rubbing some particles from the coarser fragments, in 

 the operation of separating them by a fine sieve. Indeed it may be doubt- 

 ed whether any proportion remained very finely divided — or in other words, 

 whether it had not been combined with acid, as fast as it was so reduced. 

 But without the benefit of this supposition, the finely divided calcareous 

 earth in the three specimens averaged only one and one-fourth grains to 

 the thousand, which is one twenty-fourth of the quantity laid on ; and the 

 total quantity obtained, of coarse and fine, is eight grains in one thousand, 

 or about one-fourth of the original proportion. All the balance had changed 

 its form, or otherwise disappeared, in the few years that had passed since 

 the application. 



Another similar trial of this soil from the same ground was repeated in 

 July, 1842, which showed that the finely divided carhonate of lime, then 

 remaining, was in quantity so small as to be barely perceptible and ap- 

 preciable. The land had then remained undisturbed by tillage for nine 

 months ; and some scattered fragments of shells were exposed to view on 

 the surface generally. For the obvious reasons stated in the preceding 

 paragraph, there will always appear an over-proportion of such fragments, 

 upon the surface of land not recently ploughed ; for this reason, as on two 

 of the three former trials, the upper half-inch of surface soil was thrown 

 aside, and the sample for examination taken immediately below. Of this, 

 2400 grains yielded two grains only of small fragments of shells, and 

 less than one grain of finely divided carbonate of lime ; whereas seven- 

 ty-two grains had been the original quantity furnished to the soil. This 

 result, with those of the earlier trials, agree precisely with what would be 

 expected from the action of acid in soil, and cannot be satisfactorily ex- 

 plained by any other doctrine.* 



* Even of this very small amount of fragments of shells found, (2 grains,) more than 

 half was of the very hard srray shells (oyster and scallop,) which seem almost 

 indestructible in soil. They must contain some chemical ingredient which enables them 

 to withstand the acid or other corroding action of soil, to which all the white fossil 

 shells, whether hard or soft, so readily yiekl in the course of time. 1 recently observed 

 a most striking proof of this well known general fact of the long durability of these 

 gray shells, and consequently their comparative worthlessness as a manure. On like soil 

 to the subject of the above trials, and near the same spot, I recently (1842) found a small 



