80 PROOFS Or NEUTRAL SOILS. 



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 60 

 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 

 mouldering state, it is incredible that the whole quantity of finely 

 divided particles derived from them should have amounted to no 

 more than these small proportions. Independent of the action of 

 natural causes, the plough alone, in a few years, uaust have pulver- 

 ized at least as much of the shells as was found. 



8th. In other case.s, 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 con- 

 tains the super-carbonate of lime, which is soluble ; but this loses 

 its excess of carbonic acid when left dry by evaporation, and be- 

 comes 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 containing 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 63.) 



[The excess of carbonic acid, which unites with lime and renders 

 the compound soluble in water, is lost by exposure of the calcare- 

 ous water to the air, as well as by evaporation to dryness. \_Ac- 

 cum's Chemistry Lime.~\ The masses of soft calcareous rock 

 which are deposited in the rapids of lime-stone streams are exam- 

 ples of the loss of carbonic acid from exposure to the air ; and the 

 stalactites in caves, the deposit of the slow-dropping water holding 

 in solution the super-carbonate of lime, are examples of the same 

 effect produced by evaporation. A similar deposit of insoluble 

 carbonate of lime, from both these causes, is necessarily made on 

 all land subject to be flooded by lime-stone waters.] 



such, has been placed in my cabinet. This shell was part of the dressing 

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

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

 1842.] 



