16 Mr. A. D. Hall and Dr. N. H. J. Miller. [Mar. 30, 



53 inches, the annual loss of lime is estimated at 630 kilogrammes per 

 hectare, almost exactly equivalent to 1000 lbs. of calcium carbonate per 

 acre. Unfortunately, the proportion of calcium carbonate in the soil is not 

 given, but the agreement with our figures for the removal of calcium car- 

 bonate is very satisfactory. 



Another consequence of some interest follows from these determinations 

 of the loss of calcium carbonate from the unmanured plots. The analyses 

 already quoted of the drainage water from the unmanured plot of Broadbalk 

 Field show about 100 parts of lime per million, equivalent to a loss of about 

 400 lbs. of calcium carbonate per acre in the surface soil instead of 

 800 lbs. estimated from the analysis of the soil. But the deep-seated waters 

 of the chalk contain on the average about 150 parts of lime per million, a 

 deep well at Harpenden, for example, yielding 158 parts per million.* 

 Assuming that the percolation through the unmanured plot on Broadbalk 

 represents the average percolation over the chalk area, then the removal of 

 chalk by solution would be in the ratio of the concentrations of the two waters 

 in question, i.e., the average annual denudation of the chalk by solution alone 

 would amount on the one estimate to 600 lbs., or on the other to 1200 lbs. 

 per acre per annum. As the specific gravity of the chalk is about 2"2, and 

 it contains from 95 to 99 per cent, of calcium carbonate, this would mean a 

 lowering of the surface by solution alone at the rate of either 1/11000 or 

 1/5500 of a foot per annum. These estimates depend upon the assumption 

 that the percolation through this unmanured plot of arable land represents 

 the percolation over the whole area of the chalk, whereas ordinary crops or 

 even grass would cause increased transpiration and allow of less percolation. 

 But on the contrary, the figure adopted for the concentration of the lime in 

 the drainage water from the unmanured plot is based on only a small number 

 of analyses and would appear to be too low. The concentration of the 

 drainage waters would be increased by any use of organic manures, by heavy 

 cropping or by permanent vegetation, all of which would increase the pro- 

 duction of the carbon dioxide causing dissolution in the soil. For example 

 the analyses of the water from the plot receiving farmyard manure every 

 year show an average of 123 parts of lime per million instead of 99 from the 

 unmanured plot. This increased proportion of lime in the water percolating 

 through ordinary land may be set off to some extent against the lessened 

 percolation due to crops, but on the whole the evidence is in favour of the 

 lower rate, so that a denudation of about 1/10000 foot per annum is a more 

 probable figure. 



The accuracy of the sampling is not sufficient to enable any conclusion to be 

 * Warington, 'Trans. Chem. Soc.,' vol. 51, 1887, p. 543. 



