CAUSE OF MILD POLAR CLIMATES. 163 



like the coal seams, and the whole of the Hampshire Eocene 

 is connected with the delta of a great river which persisted 

 throughout the accumulation of the various beds, which 

 aggregate to upwards of 2000 feet in thickness. This river 

 evidently flowed from the west, through a district of which the 

 low ground had a tropical climate; but like some tropical rivers 

 of the present day, such as the Brahmaputra, the Megna, the 

 Ganges, &c, it was probably fed by tributaries flowing from 

 a mountain region supporting zones of vegetation of all 

 kinds from the tropical to the Arctic, if during the Eocene 

 period vegetation such as the present Arctic had come into 

 existence, of which we have as yet no evidence. Torrential 

 floods may have swept the remains of vegetation from the 

 temperate zones of this region into tributaries that conveyed 

 it into the main river before it was decayed or water-logged, 

 where it became intermingled with the remains of vegetation 

 which grew in the tropical low ground skirting the main 

 stream, so that both sank together into the same mud 

 and silt."* 



The elevated mountain regions from which he sup- 

 poses these temperate forms were derived, he thinks, 

 might have been Mull, 400 miles N.N.W., and Wales 

 200 miles N.W. of the Hampshire deposits. Mr. 

 Gardner, however, showed most conclusively that Mr. 

 Wood's theory was based on imperfect acquaintance 

 with the conditions of the problem. The following is 

 Mr. Gardner's reply : — 



" The leaves have never been drifted from afar ; they are 

 often still adhering to the twigs. The leaves are flat and 

 perfect, rarely even rolled and crumpled, as dry leaves may 

 be, if falling on a muddy surface ; still more rarely have 

 they fallen edgeways and been embedded vertically. They 

 are, moreover, not variously mixed, as they should be if 

 they had been carried for any distance, but are found in 

 local groups of species. For example, all the leaves of 



* "Geological Magazine," 1877, p. 96. 



