1864.] Note on a tank Section at Sealdah. 157 



afforded thereby of a general depression of the delta. * The trees In 

 question, specimens of which I submitted to Dr. Anderson, were 

 pronounced by him to be Sundri, a species, the range of which, as 

 regards level, is restricted to from 2 to about 10 feet below high 

 water mark. It grows only on mud, or where the surface is too 

 frequently flooded to allow of the growth of grass, but at the same 

 time it requires that its roots be exposed to the air for at least 

 several hours of each tide. It is evident therefore that the trees at 

 Sealdah could not have grown at the level at which they are now 

 found, but that unless low water level in the Hoogly be 18 or 20 

 feet above that of the outer Soonderbuns, (where the Sundri now 

 grows,) there must have been a depression of the land surface to a 

 depth of several feet since they grew. I have not been able to obtain 

 any data showing the relative low- water levels of the Hoogly and 

 the outer Soonderbuns,f but Mr. Leonard informs me that there is but 

 very little difference between the levels of the Hoogly and the Mutlah 

 at Canning town, and this is not many miles above the actual geo- 

 graphical range of the Sundri, while the channel is so broad and deep 

 as to forbid the assumption that there should be any material elevation 

 of the low tide level of the former. 



I think therefore we may safely infer, remembering the range of 

 the Sundri, and that it never grows to within 6 or 8 feet of the lowest; 

 tide levels, that there must have been a depression of land to not less 

 than 18 or 20 feet, since the trees grew, the stumps of which are now 

 found at the bottom of the Sealdah tank. 



If at the Fort, the wood found above and below the peat bed be, 

 in situ, as I think most probable, there must have been a depression 

 at this spot to a depth of not less than 46 to 48 feet ; but whether 

 the two land surfaces thus indicated were contemporaneous, and the 

 relative depression, consequently, unequal to the extent indicated by 

 these figures, the evidence before us, is I think, insufficient to establish. 



# Or rather, additional evidence, for several proofs of subsidence were 

 afforded by the section of the Fort boring. 



f Since the above paper was read before the Society, I have obtained from 

 Col. Gastrell and subsequently from Major Walker's Eeport of the operations of 

 the G. T. Survey the accurate height of the sea level at Kidjiri with refe- 

 rence to Calcutta. 



The mean height of sea level above the Calcutta datum line of Kydd's dock 

 sill is 9,053 feet : the mean height of neap low tide levels above the same datum 

 line, 5,51 feet. The height of the ground surface at Sealdah above the datum 

 line is 22 feet, and therefore 16,49 feet above low tide level at Kidjiri. 



Hence the tree stems at the bottom of the Sealdah tank are (30 — 16,49)™ 

 13,51 feet below the mean level of neap low tides. 



