394 A. Ti/lor— Formation of Deltas. 



peat or turf being dredged up off the coast of Eranee— Pas de 

 Calais — by fishermen. 



Taking the facts as they stand in the writings of these authors, 

 who have all treated the subject most skilfully, the hypothesis of a 

 gradual fall in the sea-level of 600 feet I think explains them equally 

 well, or better, than that of local elevations, or than depressions to 

 exactly the same j)oint. The great difiiculty in Forbes's chain of 

 argument was to get the Scandinavian flora across the sea. It was 

 necessary to suppose that the space now occupied by the German 

 Ocean was elevated (of which there is no proof), in order to provide 

 dry land for the plants to pass over. The glacial mollusca were found 

 by Forbes living in the deeper portions of the German Ocean, which, 

 I think, showed that there could have been no great elevation of the 

 sea-bottom. Whether the sea-level were reduced or the land raised 

 600 feet, would have the same effect in producing changes of climate 

 and increased excavating power of rivers ; and I think all the phe- 

 nomena of a great northern river receiving the waters of the Ehine, 

 Thames, Humber, etc., would occur as described by Mr. Godwin- 

 Austen, if the sea-level were depressed 600 feet. 



Mr. Godwin- Austen states that the level of the Eed Crag strata 

 and of the Thames Valley was, at the period of the Eed Crag, at 

 about the same level as it is now. See plate in vol. vii., page 136, 

 Quart. Journ. Geol. Soc, 1851. But he tells us that the land in 

 question has undergone great oscillations in the intervening period, 

 and has returned to its old level, p. 136, vol. vii., Quart. Journ. 

 Geol. Soc, 1851. 



No proof of such a movement is offered, and it would appear as if 

 Mr. Godwin- Austen suggested such oscillations of level principally 

 to justify him in attributing an arctic climate to this part of England, 

 such climate being indicated by the terrestrial flora and marine 

 fauna, and subaerial gravel in the Quaternary Period. Now the 

 hypothesis of a great fall in the sea-level and subsequent rise of the 

 water to the same point would, I think, explain satisfactorily the 

 occurrence of great subaerial beds of gravel with fluviatile and ter- 

 restrial remains, without the necessity of supposing an immense 

 elevation of England and a subsidence afterwards to exactly the 

 same point. 



I say exactly, because the Crags and fossiliferous gravel deposits 

 are situated on a very narrow and level horizon. A fall in the land, 

 now, of fifty feet, would immerse every portion of the Eed and 

 Norwich Crags, and of the fossiliferous gravels containing Cyrena. 

 The Coralline Crag is found a few feet higher than the others. 



The top of the Eed Crag and of the Cyrena sands in the Thames 

 and Humber Valleys reach the same height within three or four feet, 

 and are all under the 50 feet range of height at the present time.^ 



Then on the English south coast and at Sangatte there are raised 

 beaches occupying similar positions as to level as the Crag in the 

 German Ocean, and containing erratic boulders at their base as in 

 the Eed Crag. 



1 Searles Wood, in a letter to A. Tylor respecting the height of the Crag. 



