John Gunn — Causes of Change of Clbnate. 77 



ranges ; and there is no reason to doubt but that, if the depression 

 continued in a sufficient degree, there wouhl be a return to the 

 temperature of more genial periods, to the Purbeck or the Oolite ; 

 or on the contrary, if the engine may be said to be sufficiently re- 

 versed, there would be a return to the Glacial epoch. 



The most remarkable evidence to this effect may be adduced from 

 the variations of the coui'se of the Gulf Stream. 



Mr. William Hopkins shows ^ that the present Gulf Stream 

 flowing through the Straits of Bahama, and thence in its north- 

 eastern direction towards the North Sea and the coasts of Europe, 

 is a current reflected from the shores of the Gulf of Mexico, in 

 consequence of the impossibility of its continuing the north-western 

 course by which it reaches the Gulf. In his masterly paper he 

 proves that its course has not always been, as at present, through 

 the Straits of Bahama, and that it would not continue to be so, if a 

 depression of the North American Continent to the amount of 2000 

 feet were to take place ; that such a depression would convert the 

 valley of the Mississippi into a great arm of the sea, of which the 

 present Gulf of Mexico would form the southern extremity ; and 

 which would communicate at its northern extremity with the waters 

 occupying the submerged district, which he described as the great 

 valley now occupied by the chain of lakes. A direct communication 

 would be thus produced between the Gulf of Mexico and the Arctic 

 Sea along the eastern base of the Eocky Mountains. 



Such would be the necessary consequence of this submergence, 

 and further Mr, Hopkins affords a very strong proof that such 

 a course of the Gulf Stream has actually existed between the Gulf 

 of Mexico and the regions of North America by the discovery made 

 by Professor E. Forbes of plants which belong to the Pleistocene 

 period along the flanks of the Eocky Mountains, and between them 

 and Hudson's Bay, being the very region in which the temperature 

 would be expected to be affected by the warm current from the 

 Gulf of Mexico. 



Such, no doubt, has been the effect produced by the change of 

 level of the North American Continent, and it is a striking fact that 

 this altered current of the Gulf Stream would have flowed in the 

 direction of Melville Island, the Miocene coal-bearing country in the 

 Arctic regions. 



I do not mean to affirm that this extraordinary phenomenon 

 would be thus satisfactorily accounted for, but the conjoint actions 

 of depr-ession of the land and influx of the Gulf Stream appear to 

 offer an explanation of this most extraordinary phenomenon of the 

 existence of a Miocene flora in so northerly a latitude. Without this 

 joint agency, we may affirm that no change in the configuration 

 of land and water, so ably advocated by Sir C. Lyell, could have 

 produced that effect. 



In addressing the Members of the British Association, I have not 

 thought it necessary to enter more fully into the particulars of the 

 changes of level and climate during the several periods mentioned. 

 ^ Quart. Jourii. Geol. Soc, vol. viii. p. 89. 



