502 W. Whitaker — On Geology and Consumption. 



Clay is favourable for holding back the same, and therefore the 

 districts formed by the two clays are quite different in this important 

 particular. 



Comparisons of the Districts taken up hy the Outcrops of the London 

 Clay and of the Weald Clay. 



Weald Clay, 

 (1). Less covered by gravel. 



London Clay. 



(1) . Often covered by gravel, especially 

 in tbe populous districts. 



(2). The capping of gravel is mostly 

 of fair thickness. 



(3). Forms a comparatively high 

 country (except in the gravel-flats 

 bordering the Thames), and is not closely 

 bordered by higher ground of other 

 formations. 



(4). Has, for the most part, a gently 

 undulating surface (except for the gravel- 

 flats). 



(5). With comparatively few rivers, 

 and those almost wholly from its own 

 drainage (except where the larger rivers 

 flow directly across it, through valleys). 



(2). The gravel is comparatively thin, 

 and often insignificant. 



(3). Forms a low country, bordered ou 

 both sides by higher ground. 



(4). Forms a flatter country, less 

 varied by undulations, and those of less 

 height. 



(6). Is a channel for many rivers, 

 which carry off not only its own drainage, 

 but also that of the higher ground on 

 either side, and which meander over it 

 for long distances, and with slight fall. 



At first sight, and in a purely geological aspect, the general result 

 of the enquiry might be summed up as follows : that the consumption 

 death-rate varies roughly as the age of the formations (disregarding 

 alluvium, gravel, &c., which are distributed pretty fairly over all) : 

 the districts of the Tertiary beds and the Chalk holding, as a rule, 

 the highest place, that is to say having the lowest death-rate ; those 

 of the Wealden beds taking the lowest place ; and those of the inter- 

 mediate Greensand, &c., coming in the middle. But this would 

 give a very illusive view, for there are many exceptions. 



Two methods of analysis of the obtained facts were used by Dr. 

 Buchanan. Firstly, grouping the registration-districts in their order 

 of consumption death-rate, to see what proportion of the population, 

 in each group, live on pervious or impervious soils. For this purpose 

 fifty of the districts (the remaining eight being left out as having 

 exceptional characters, and needing further examination) were classed 

 in five groups of ten each, vsdth the following result : — 



Groups of Ten Registration Districts. 



1. With Lowest Consumption Death-rate 



2. „ Higher „ „ 



"• » ft )) )> 



4. „ 



6. With Highest Consumption Death-rate 



Percentage of Population. 



r- 

 On Pervious 



On Impervious 



Soils. 



Soils. 



90-9 



91 



87-7 



12-3 



79-5 



20-5 



79-2 



20-8 



64-2 



35-8 



These gross results, though at first sight more exact than the 

 rough general result first given, are however open to many 

 objections, one of the chief, in a geological point of view, being 



