136 S. R. Elson — Gurrents and Tides of the Hugli. [Nov., 



bottom is of a very soft blue clay, with a tenacious substratum which 

 holds the sounding lead much too firmly, sometimes with such tenacity 

 as to break the line. 



But the eastern edges of the whole of them shelve very gradually, 

 and consist of hard, fine sand such as is found high up in the Hooghly. 

 This fine sand has, in very disturbed states of the sea, been deposited 

 on the rigging of vessels, when these have been in from 12 to 15 

 fathoms of water, shining, when dry, like particles of steel filings. 



As elsewhere, the tides of the Hooghly seem to be very much in- 

 fluenced by varying conditions of relative baric pressure over sea and land 

 areas ; both diurnal, when, in the afternoon, within 100 miles of land, the 

 sea area has the superior pressure and vice versa in the forenoon : and 

 yearly or as termed in the tide tables, ' seasonal,' when, from October (as 

 Mr. Blanford tells us, ' the land area is suddenly transformed into a 

 region of high pressure ') to March, the pressure is higher to the north 

 than to the south, and vice versa, when, the sea area becoming the seat 

 of highest pressure, southerly winds as a necessary result, predominate, 

 and raise a high swell at the Sandheads ; this swell becoming more 

 agitated in the shoal water of the estuary is, of itself, doubtless, a cause 

 of the waters of the river standing higher ; but, taken in conjunction 

 with the steepened baric gradient and southerly wind, the mean level 

 of the water in the river rises steadily till the advent of the light- 

 er fresh water in the rains, when it stands higher still, or about 

 four feet higher in September than in January and February, when 

 salt or brackish water reaches far up the river. (In June of this year, 

 immediately before the freshets had set down, I found five and a half 

 grains at low, and five and three quarter grains of salt per ounce troy at 

 high water, at Diamond Harbour.) 



Any abnormal state of the usual relative baric pressure causes a 

 corresponding disturbance in the predicted regularity of the tides, both 

 in times and heights of low and high water : the water, as above-men- 

 tioned, responding to the altered baric gradient before the air has time 

 to do so, much less to raise waves outside, which, of themselves, are 

 known to augment, or exalt, the calm mean sea level. 



From low to high water, in the whole of the river, is a little more 

 than five hours ; and from high to low water a little more than seven 

 hours : but the flowing and ebbing of the water is greatly influenced by 

 the strength of the freshets, and the distance from the sea : so that at 

 Calcutta, in the month of September, vessels in the neap-tides, 

 do not swing to the flood : and, owing to an extraordinary freshet this 

 year, vessels did not swing flood in the height of a perigee spring tide ; 

 but this masking of the flood stream does not affect the rise and fall of 

 the tide, which goes on all the same as the tide tables predict. 



