1854.] On the quantity of Silt held in suspension. 283 



This little area is interesting only as proving the former extension 

 of the formation to which these rocks belong, but is economically, of 

 no value whatever, 



No. 334. 



Copy of this letter and of its enclosure forwarded to the Asiatic 

 Society. 



On thv quantity of Silt held in suspension hy the waters of the 

 Hooghly at Calcutta, in each month of the year. By Henry 

 Piddington, Curator, Museum of Economic Geology. 



I some years ago (1842) collected for examination a set of two 

 bottles of the waters of the Hooghly taken on the 1 st of each 

 month, at noon, at Calcutta and at Burisaul, with the view of ob- 

 taining a fair average of the actual amount of silt held in suspension 

 by the waters of the Hooghly and the Burrampooter near their 

 mouths. The time of tide was purposely neglected, as either high 

 or low water, or any intermediate term between these would have 

 given a result perhaps farther from a fair average than taking it at 

 all times. 



One set of these bottles I sent to professor Ehrenberg for his 

 researches on the Infusoria^. His reply did not reach me, but Dr. 

 Falconer informed me that he had received them and spoke highly 

 of the curious results he had obtained. A press of other matter 

 prevented me from following out the enquiry I then proposed to 

 myself, and the bottles remained in the Museum. 



In the course of some private researches connected with ques- 

 tions arising in ray mind as a member of the Hooghly Eiver Com- 

 mittee, I was again desirous of ascertaining the average amount of 

 silt, and I fortunately found that 11 out of 12 of the Hooghly* 

 water bottles were yet forthcoming, but only seven of those from 

 Burisaul ; but the loss of these last was not so much to be regret- 

 ted, as Burisaul is not favourably situated for the collection of 

 specimens of water from the great Ganges. The results here stated 

 then relate to the Hooghly only, at Calcutta. 



2 P 2 



