A. Tylor — Formation of Deltas. 393 



hypothesis of a fall in the sea-level seems to accord better with the 

 facts he described, than his supposition of changes of level of the 

 land and sea bottom. 



If the hypothesis is correct, that there has been a fall of the sea- 

 level of 600 feet during the Glacial Period, followed by an equiva- 

 lent rise, we ought to find evidence of dry land, of rivers, or at 

 least of littoral conditions, on the bottom of the sea within the 100 

 fathom line of soundings. 



We should not expect to find a very continuous and unbroken 

 land-surface preserved, as in the upward movement of the sea 

 much ground would be covered with deposits of clay, and shingle, 

 and sand, and much of the old surface removed by currents and 

 waves. 



De la Beche, Edward Forbes, and Godwin-Austen have investi- 

 gated the present condition of the sea-bottom round the British Isles, 

 and in their writings are to be found many observations of facts that 

 may be as conveniently explained by the hypothesis of the change 

 in the sea-level as by that of a change in the level of the land and 

 sea-bottom. 



Mrs. Somerville writes (p. 219, Physical Geography) : "By sound- 

 ings during the Coast Survey of the United Kingdom, it appears that 

 Great Britain and the innumerable islands and rocks that rise above 

 the surface of the sea repose upon a submarine bank, bounded by a 

 line 100 fathoms deep ; and this bank, on which Great Britain and 

 all its islands stand, is connected on the south-east through Holland 

 and Belgium with the Continent of Europe." 



Sir H. T. De la Beche (page 192, Theor. Eesearches) remarks : — 

 "If the British Islands were elevated one hundred fathoms above 

 the level of the ocean, and thus joined to the Continent of Europe, 

 they would be surrounded by an extensive area of flat land : for the 

 fall from the old sea-coasts to the new sea-coasts would be generally 

 so gradual as to present to the eye one great plain." 



In the Quart. Journ. Geol. Soc, vols. vi. and vii., 1850 and 

 1851, God win- Austen gave maps of the English Channel and 

 German Ocean, and records littoral accumulations, mammalian re- 

 mains, and freshwater shells in situ, although at depths reaching 

 nearly to 100 fathoms. He boldly mapped out a diagram of the 

 course of a great ancient river which ran 400 miles north, receiving 

 the waters of the Ehine, Thames, Humber, Tweed, and Tay, having 

 its mouth near the 100 fathom line between the coast of Scotland and 

 the entrance to the Baltic Sea. Plate 7, vol. vii., Quart. Journ. 

 Geol. Soc, 1851. He also produced evidence of the former course 

 of the river from soundings, and by the presence of fossil mam- 

 malia dredged up from near its course. He records that Captain 

 White dredged up TJnio pictorum between the 50 fathom and 100 

 fathom line off the mouth of the English Channel, and that marine 

 gravel banks (with littoral shells), formed at the surface of the sea, 

 are now lying under sixty or seventy fathoms of water in the same 

 locality (p. 96, vol. vi. Quart. Journ. Geol. Soc, 1850). In vol. ii. 

 Quart. Journ. Geol. Soc, p. 117, Mr. Godwin- Austen records beds of 



