W. Whitaker — On Geology and Consumption, 503 



that the physical features of the districts are not taken into account, 

 and therefore the classification of the soils as pervious and imper- 

 vious is in some cases delusive ; for a veiy low-lying tract of 

 pervious beds may, from its position, be saturated with water that 

 cannot escape, and would therefore be in no better case, as regards 

 the draining away of water, than a tract of impervious beds ; indeed 

 not so well off perhaps as a high-lying sloping tract of the latter kind. 



The second method of numerical analysis adopted by Dr. 

 Buchanan was calculated to lead to more exact and valuable results. 

 Its pl£in was, to quote his own words, "to select out of the fifty- 

 eight districts such as are most comparable with each other in regard 

 of their position and geological structure, and to see how their 

 phthisis is affected by the perviousness or imperviousness, elevation 

 or lowness, slope or flatness, in the members of such more limited 

 series," a method which involved various comparisons of districts 

 and formations. 



Firstly, as regards the amount of consumption on pervious soils 

 from which water can drain away, compared with that on more 

 impervious or retentive soils. The great tract known as " the 

 Weald," contains within itself good materials for such a comparison, 

 the districts that are chiefly on the more sandy and more sloping 

 Hastings Beds contrasting with those on the flatter Weald Clay. 

 In no case indeed is a district wholly sand or wholly clay, but the 

 proportion of the population living on clay or on sand varies greatly ; 

 moreover many of the districts are partly on other formations. 

 Parts where the Weald Clay is covered by gravel, being of an inter- 

 mediate character, were treated as half pervious and half retentive. 

 There were found to be fifteen registration-districts in which the 

 greater part of the population lived on the various divisions of the 

 Wealden series, and an examination of these showed that the 

 districts with the higher consumption death-rates have the larger 

 proportion of their population on retentive beds, and that those with 

 the lower rates have the larger proportion on the more pervious beds ; 

 the numbers varying from 95 per cent, of the population on per-vdous, 

 and 5 per cent, on retentive soils in the case of Hastings (which, 

 after proper correction has been made for the influx of invalids, 

 seems to be the second best district on the Consumptive Bill of 

 Health), to 30 per cent, and 70 per cent, respectively in the case of 

 Petworth, which is the worst district but two out of the whole fifty- 

 eight. 



Like results were got by the comparison amongst themselves of 

 the ten districts in which the greater part of the population live on 

 the Lower Greensand. 



Secondly, a comparison was made between districts composed 

 mostly of pervious soils at a fair height and with a good slope, in 

 short in which there were good facilities for the draining away of 

 water ; and other districts of like beds, but which from their position 

 and character were more liable to saturation. In this case the slope 

 of underlying impervious beds is sometimes important, as a shallow 



