52 CALCAREOUS MANURES— THEORY. 



The very small proportions of finely divided calcareous earth compared 

 to the coarse, in some shelly soils, furnish still stronger evidence of this 

 kind. Of the York river soil, (described page 38 No. 5,) 

 1260 grains, yielded of coarse calcareous parts, - - 168 grains. 

 And of finely divided, 8 



1044 of the rich Nansemond soil, (No. 6,) - - - 544 coarse. 



18 fine. 



As many of the shells and their fragments in these soils are in a mould- 

 ering state, it is incredible that the whole quantity of finely divided particles 

 derived from them should have amounted to no more than these small pro- 

 portions. Independent of the action of natural causes, the plough alone, in 

 a few years, must have pulverized at least as much of the shells as was 

 found. 



8. In other cases, where the operations of nature have been applying 

 calcareous earth for ages, none now remains in the soil ; and the proof 

 thence derived is more striking than any obtained from artificial applications 

 of only a few years' standing. Valleys, subject to be frequently flooded 

 and saturated by the water of lime-stone streams, must necessarily retain a 

 new supply of calcareous earth from every such soaking and drying. 

 Lime-stone water contains the super-cai'honate of lime, which is soluble ; 

 but this loses its excess of carbonic acid when left dry by evaporation, and 

 becomes the carbonate of lime, which not being soluble, is in no danger of 

 being removed by subsequent floods. Thus, accessions are slowly but 

 continually made, through many centuries. Yet such soils are found con- 

 taining no calcareous earth — of which a remarkable example is presented 

 in the soil of the cultivated part of the Sweet Spring Valley, (No. 8, 

 page 40.) 



The excess of carbonic acid, which unites with lime and renders the com- 

 pound soluble in water, is lost by exposure of the calcareous water to the 

 air, as well as by evaporation to dryness, [Accum^s Chemistry — Lime,] 

 The masses of soft calcareous rock which are deposited in the rapids of 

 lime-stone streams are examples of the loss of carbonic acid from exposure 

 to the air ; and the stalactites in caves, the deposite of the slow-dropping 

 water holding in solution the super-carbonate of lime, are examples of the 

 same effect produced by evaporation. A similar deposite of insoluble car- 

 bonate of lime, from both these causes, is necessarily made on all land sub- 

 ject to be flooded by lime-stone waters. 



9. All ivoocl ashes contain salts of lime, (and most kinds in large propor- 

 tions,) which could have been derived from no other source than the soils 

 on which the trees grew. The lime thus obtained is principally combined 

 with carbonic acid, and partly with the phosphoric, forming phosphate of 

 lime. The table of Saussure's numerous analyses of the ashes of nume- 

 rous plants,* is sufficient to show that these products are general, if not 

 universal. The following examples of some of my own few examinations 

 prove that ashes yield calcareous earth in proportions suitable to their kind, 

 although the wood grew on soils destitute of that ingredient — as was as- 

 certained with regard to each of these soils. 



and thin but well-marked oyster-shell, (Ostrea Virglniana,) apparently as perfect and 

 as well preserved as when it was dug up, and which was a <jood characteristic specimen 

 of the kind, and as such, has been placed in my cabinet. This shell was part of 

 the dressing spread upon the field for the crop of 1821, and has been since exposed to 

 all the vicissitudes of tillage and of weather for nearly twenty-two years. 

 * Quoted in Agr. Chem. Lecture 3. 



