1856.] 



Silt held in suspension in the Hooghly. 



161 



Comparing now the results of our estimated mean average at 

 Calcutta as given at p. 156 with these at the Gasper, we find them 

 as follows. 













a> 



T3 'T$ 







>>*S 



O 





a 



^3 S S3 

 O £ cS 







r& i ~ i 













^*S 







*ti A 



fl -is . 





Water, 

 oz. 



u °° 



OS U 

 02 



cS 



M a 



U •-! 

 03^ 

 O 



o 



a 



feiD 



03 



° 9 



XII 



Total of 

 matter i 

 ter ; sil 

 solution 



Calcutta, 



24.51 



6.03 



4.63 



0.00 



0.00 



10.66 



Oasper channel, 



24.89 



1.69 



6.94 



7.60 i 



2.03 



18.92 



So that we find that three-fourths of the more earthy detritus 

 is already dispersed by being diluted by the water of the ocean, and 

 indeed if the whole were to be deposited the river channels would 

 quickly be choked up, and that the sea water has largely added mag- 

 nesia as an element to the salts in solution ; for the river water at 

 Calcutta which always contains a sufficiency of lime shews, as will 

 be observed (p. 153), only a trace of magnesia as the hunhurs are 

 found to do. 



I thought it well worth while also, to know what is really the time 

 which the whole of the sediment in the water takes to settle, and I 

 found that the silt of the surface water of the Hooghly, in the 

 month of November, took exactly nine days to sink through one foot 

 of water in a cylindrical glass vessel ! this rate would give fifty-four 

 days for a single fathom ! and in salt or brackish water the rate 

 would be still slower from its greater density ; and this accounts for 

 the finer sediment being carried so far out to sea, and for the slow 

 rate of decrease of soundings in the sea channels and on the Sand 

 Heads or ridges which extend along the head of the Delta. 



Postscript. 



In connection with this research, and as affording us some little 

 light as to the processes going on in the river, I may here mention 

 that I have been favoured by Mr. Bensley, H. C. Pilot Service, now 

 the river-surveyor, with two very interesting specimens ; being a kun- 

 Jcur now forming on the beach at Kedgeree and some dredgings 

 from Lloyd's Channel which is between Kedgeree and Saugor roads, 

 I describe them in the order in which I have mentioned them. 



