478 



NATUKE OF THE STEATA 



[Ch. XIX. 



from 



preceded him, has argued that the sediment is thrown down 

 in consequence of the overflowing river being checked by 

 meeting with the still water of the jheels or lakes correspond- 

 to those seen at #/and d e, fig. 31, p. 443. In point of 

 fact, however, the deposition of the coarser matter takes 

 place immediately on the highest part of the banks where the 

 waters first begin to overflow and before thfljjr reach those 

 lakes which occur at a lower level in the alluvial plain on each 

 side of the main river. The banks are of equal height and 

 as continuous where no jheels exist. 



No 



Brahmapootr 



nearer the sea 



miles 



Yet it is remarkable that the boring of an 

 Artesian well at Fort William, near Calcutta, in the years 

 1835 — 1840, displayed, at the depth of 120 feet, clay and sand 

 with pebbles. This boring was carried to a depth of 481 feet 

 below the level of Calcutta, and the geological section obtained 



in the operation has been recorded with great care. Under 



the surface soil, at a depth of about ten feet, they came to a 

 stiff blue clay about forty feet in thickness ; below which was 

 sandy clay, containing in its lower portion abundance of de- 

 cayed vegetable matter, which at the bottom assumed the 

 character of a stratum of black peat two feet thick. This peaty 

 mass was considered as a clear indication (like the ' dirt-bed 

 of Portland) of an ancient terrestrial surface, with a forest or 

 Sunderbund vegetation. Logs and branches of a red-coloured 

 wood occur both above and immediately below the peat, so 

 little altered that Dr. Wallich was able to identify them with 

 the Soondri tree, Heritiera littoralis, one of the most prevalent 

 forms at the base of the delta. Dr. Falconer tells me that 

 similar peat has been met with at other points round Calcutta 

 at the depth of nine feet and twenty-five feet. It appears, 

 therefore, that there has been a sinking 1 down of what was 

 originally land in this region, to the amount of seventy feet 

 or more perpendicular ; for Calcutta is only a few feet above 

 the level of the sea, and the successive peat-beds seem 



to 



* Fcrgusson, ibid. 



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