GLEANINGS 
IN 
SCIENCE. 
No. 19. — July, 1830. 
I— On the Salt- Water Lakes in the Vicinity of Calcutta ; with sug- 
gestions for filling them up Inj JVarping. 
The position of a European city of such importance as Calcutta, upon the very 
borders of an extensive salt marsh, of which the insalubrity is so generally ac- 
knowledged, has often awakened the surprise of intelligent, strangers. Nor is it 
easy to adduce reasons, why the recovery to cultivation of so large a tract has not 
before the present moment become an object of consideration to an enlightened 
Government resident on the spot. 
The inhabitants of the infant factory of Calcutta might with some reason look 
for security in the proximity of an immense impenetrable morass upon their 
flank, and as a defence, would endeavour, with jealous care, to preserve it in the same 
state. But the residents in the capital of an empire no longer exposed to prae- 
datory inroads, must view it in a different light. Health and appearance have 
long taken the place of security and defence, as objects to be kept in view in the 
local improvements of the place ; and there is only one way of accounting for the 
subject having escaped attention, which offers any probability of truth. It would 
seem that the idea of the lake being necessary to the military defence of the city, 
has been succeeded by an impression not altogether unfounded, and which ap- 
pears yet to be rather generally entertained ; viz. that the existence of the salt 
marsh in its present state is indispensable to the perfect drainage of the town. 
Upon this point, then, it is necessary to be most particularly informed, before 
any measures are proposed that would interfere in any way with the present 
system, whether that system he effective or otherwise. I shall offer my observa- 
tions upon this point in the first instance, and hope to place the subject in such a 
light, that its reference to any scheme counected with the city will be at once 
comprehended. 
The river Hooglv, the western boundary of the delta of the Ganges, as well 
through its connection with the great river as from the streams flowing into it from 
the west, is subject to an annual rise, technically called the freshes , commencing 
in June and terminating in October. In the central expanse of the delta there 
are likewise several streams, having connection with the Ganges, which are subject 
to the same influence, rising at the season named, according to the quantity of 
influx of fresh water from the Ganges. 
Tbe surface of the delta intervening between these, is divided into a perfect 
labyrinth by tide backwater creeks, which are subject to no other change of level 
during this season, than what is derived from the vicinity of the great discharge 
of water from the embouchures of the great river, and the effect of this discharge 
upon the tides in the upper part of the bay of Bengal ; added to the trifling dis- 
charge of rain water upon the surface of the coifttry immediately in contact with 
the creeks. 
Calcutta is situated on the Hoogly, below the parallel of latitude to which these 
tide backwaters are found to run ; for in the general slope of th£ surface of the 
delta from its upper fork at Jellingi to the sea, there is of course a limit beyond 
which the tide influence could not extend. And this city built along tbe crest of 
the high banks of the river, which are generally above the elevation of its highest 
known floods, has, immediately behind it, an expanse over which the tides of these 
backwaters spread, thus dissipating part of their force and elevation. 
I may mention here that it is a general principle of these creeks, that they 
either possess at their upper termination a jhil of this nature, over which they 
spread and dissipate their force, or else when they are connected with a continued 
