256 



Cholera in Relation to Certain Physical Phenomena. [part i. 



of the separate annual tables, that it is during April that conditions favouring the disease 

 are most commonly present. 



Average monthly Eainfall 8-20 years ; 

 [Inverted curve]. j 



Average monthly Water-level, 2-3 

 years [Inverted curve]. 



Total Cholera [15 years] 



Bililiiiliiiii 



EQII 

 SHI 



■— ^ HI ill I imiii'iaiw 



 ■Ml 



-10 feet from surface of ground. 



-2 feet from surface of ground. 

 -Maximum Cholera in March. 



Diagram 13. — Illustrative of the average monthly Rainfall, Water-level, and total monthly 



Cholera at Berhampore. 



(c) Dinapore— a transition area : Geological and Meteorological features. 



Dinapore may be said to furnish an illustration of a station in a district forming a 

 sort of border-land between the endemic area and the parts of the country in which 

 experience has shown that cholera is less prone to be constantly present. 



It is situated on the south bank of the Ganges, and geologically may be said to 

 present precisely similar conditions to those of the other alluvial stations to which 

 reference has been made. 



In a memorandum regarding the sites of Military stations in India, Dr. Oldham, 

 formerly Superintendent of the Geological Survey, states, with reference to this group, 

 that " the conditions of the several stations on the banks of the Ganges are pretty nearly 

 the same, that is, Calcutta, Dum-Dum, Barrackpore, Berhampore, and Dinapore, so far as 

 the geological structure of the ground on which they are placed is concerned, may be said 

 to be similar. They are all built on a series of beds of silt, fine sand and clay of immense 

 thickness, and varying much in the succession. These beds are generally quite or very 

 nearly horizontal, and the character of the surface varies according as the uppermost bed 

 at the place is sand or clay. Not one of these places does or can afford any natural drainage. 

 Soil will, of course, absorb and drink in a large amount of moisture and of impurities also, 

 but there is no means by which these can pass off, and they therefore accumulate. The 

 ground, in fact, licks up moisture and sewage as a sponge would, and as a sponge it also 

 loses these by evaporation, only overflowing when full, but nothing more." 



At this part of the country, however, the character of the alluviuvi begins to give 

 evideTwe of a change — a transition from the more recent Gangetic to the old alluvium 

 (^oide page 260). 



The rainfall also undergoes a considerable diminution, for instead of being over 

 60 inches, as in Calcutta, Purneah, Berhampore and other stations, an average of only 



