Nortvich Geological Society. 577 



quantity of water in the sea remained the same, would to some ex- 

 tent be counteracted by the reduction in vohmie consequent on the 

 formation of the ice. AVith regard to the delta of the Mississippi, the 

 data on which he argued had considerably altered since first he wrote 

 on the subject, inasmuch as recent calculations had doubled the esti- 

 mated volume of water flowing into the sea, and thus it was capable 

 of producing the same efiect in half the previously calculated time. 

 The progress of the delta at any spot was of necessity variable, as 

 the position of the mouth changed. The American engineers had 

 allowed only 40 feet as the depth of the fluviatile deposits, whereas, 

 from boring, Sir Charles had concluded it to be at least 500 or 600 

 feet. There was now reason to suppose that it was much more, pos- 

 sibly as much as 1500 feet. This being the case, notwithstanding 

 the amount of work done by the river being doubled, his calculation 

 as to the time required for the formation of the delta might not after 

 all be so excessive. 



Mr. Prestwich suggested that Mr. Croll's theory only involved a 

 transfer of ice from one Pole to the other, and not a diminution of 

 volume of the sea. The raised beaches round the coast of Britain 

 varied considerably, and were not on one uniform horizon, as they 

 would have been had they resulted from a lowering of the sea. 

 The elevation of the old sea-beds during the Glacial period were not 

 accounted for by any supposition of the mere alteration in the 

 volume of the sea. 



Mr. Evans pointed out that, the Cyrena being a fresh-water shell, 

 its position at a certain level was not connected directly with the 

 height of the sea. He doubted the curve of the rivers being in all 

 cases parabolic. 



Mr. Mallet had already remarked that the beds of rivers, especially 

 near their sources, appeared to assume curves closely allied to a para- 

 bola. He considered that the form was due rather to the elevatory 

 forces than to erosion. He doubted, however, whether they were 

 really parabolic curves, or, indeed, any other mathematical curve. 



Mr. Tylor replied that he had not found definite evidence as to the 

 extension of corals downwards to such a depth as that mentioned by 

 the President. With regard to oscillation, he had merely treated 

 of the southern part of England. The opening of the Straits of Dover 

 would account for the existence of beaches above the present level, 

 as the tides would have previously risen higher. The parabolic 

 curve was that which, by actual comparison, coincided most closely 

 with the longitudinal section of the banks of the rivers Po, Mississippi, 

 and Ganges. 



Norwich Geological Society. — I. The monthly meeting of this 

 society was held at the Museum on October 6th, and was well 

 attended. The President (the Eev. J. Gunn, F.G.S.) was in 

 the chair. 



Mr. Charlesworth, F.G.S., read the following paper, " On the 

 Prospective Annihilation of the Suffolk Eed Crag as a Geological 

 Formation, with a few Remarks about the Red Crag Phosphatio 



