1854.] On the quantity of Silt held in suspension. 285 



only, when separated from the amount of Carbonate of Lime which, 

 as will be seen below, it was both necessary, and of great interest 

 to obtain. Column D shews the amount of Carbonate of Lime ; 

 and herein a very curious fact, which is of much geological import- 

 ance was disclosed, namely, that in some months so large a portion 

 of Carbonate of Lime is held in solution by the waters of the 

 Hooghly, that, as the Carbonic Acid evaporates, it is deposited in a 

 crystalline crust at the neck and on the sides of the bottle, and in a few 

 of these months it even forms a small cup-shaped stalactite on the 

 apex of the bottom of the bottle ! adding thus very largely to the 

 actual solid contents of the water when we come to consider them 

 geologically.* 



The table thus shews, as a mean result, that while the average of 

 other earthy solid matters amounts only to 6.04 grains, the car- 

 bonate of lime amounts to 7.95 grains, or nearly one-third more in 

 weight ; so that a rock formed of such silt would contain in round 

 numbers 60 per cent, of carbonate of lime ! or be in other words 

 a good Kunhur ! 



Reducing the fluid (apothecary's) ounces of water to cubic mea- 

 sure at 1.73296 inches to a cubic ounce, the average quantity of 

 water 25.33 oz. will be equal to 43.89587 inches ; which, to save 

 decimals, we may call 43.90 cubic inches of water, containing 13.99 

 grains of silt ; which for a cubic foot will give 550.677 grains or 

 1 ith of an ounce by weight of solid silt ! 



I had also collected a small quantity of the silt deposited in the 

 tanks in which the river water at Chandpaul Ghaut is pumped up 

 for the aqueducts of the town, which contains, I find, 10.85 per cent, 

 of calcareous matter, and taking this to be the average of the silt, 

 I found that a cubic inch of it, moistened and beaten hard, and 



* In a paper " On the fertilizing, principle of the inundations of the Hooghly ," 

 published in vol- xviii. of the Society's Transactions twenty years ago (1833) I 

 shewed, page 224, that lime, and not vegetable matter, was probably the fertiliz- 

 ing principle of the silt of the Hooghly, in which it was found to exist to the 

 amount of 6 per cent, I also shewed that the drainings from the mud were highly 

 impregnated with carbonic acid holding lime in solution. Sir Charles Lyall, Ele- 

 ments of Geology ; page 89, vol. I. of edition of 1841, says in reference to this, 

 that it throws great light on the mineralization of organic bodies. 



