8 PROCEEDINGS OP THE GEOLOGICAL SOCIETY. [NoV. 11, 



liypothesis of a fall in the sea-level, in the author's opinion, accords 

 better with the facts described than Professor Forbes's supposition 

 of changes in the level of the land and sea-bottom. 



If Mr. Tyler's hypothesis is correct, that there has been a fall of 

 the sea-level of 600 feet during the Glacial period, followed by an 

 equivalent 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 shiugie, and 

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



Sir Henry De la Beche, Professor Edward Forbes, and Mr. God- 

 win-Austen have investigated 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. 



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, the author thinks, explains 

 them equally well or better than that of local elevations and then de- 

 pressions to exactly the same point. The great difiiculty in Professor 

 Forbes's 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 Professor Forbes living in the deeper portions of the 

 German Ocean, which, the author thinks, 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 he thinks that all the phenomena of a great northern 

 river receiving the waters of the Rhine, Thames, Humber, &c. would 

 occur as described by Mr. Godwin- Austen, if the sea-level were de- 

 pressed 600 feet. 



Mr. Gwyn JeiFreys has lately recorded the discovery of specimens 

 of fossil Arctic shells off the Shetland Isles in about 90 fathoms 

 water. The following species were found by him in dredging, and 

 are arranged in the order of their abundance : — 



Terebratula Spitzbergensis. 



Rhynchonella psittacea. 



Pecten Islandicus. 



Tellina calcarea. 



Mya truncata, yar. Uddevallensis. 



Trochus cinereus. 

 Molleria costulata. 

 Trophon clathratus. 

 Columbella haliseeti. 

 Pleurotoma pyramidalis. 



All these sheUs are found fossil in Sweden, and living in the 

 extreme Arctic seas. I^one of these species are ever found in deep 

 water ; so that their presence, scattered over a wide area of sea- 

 bottom, is remarkable, and corresponds with the discovery of shingle 

 and littoral shells in the English Channel at similar depths. The 



