470 Mr. Bowman on the question, Whether there are 



doubted evidence of the former greater extent of glaciers may 

 be gradually traced from the warm valleys of the Alps up to 

 the actual feet of existing glaciers, the greater altitudes of the 

 mountains and increased distance from the modifying influ- 

 ence of the sea, will be found more than adequate to compen- 

 sate for their being situated ten degrees nearer to the equator. 

 In this view it is therefore possible, assuming the theory of 

 Prof. Agassiz of a general reduction of temperature in ancient 

 times over the whole northern hemisphere, that Switzerland 

 might be covered with ice and snow, while Britain might be 

 comparatively free from them. But this reasoning, though 

 plausible on a cursory glance, falls to the ground, if we ac- 

 cept the theory of this distinguished philosopher, that the gla- 

 cial period occurred antecedent to the elevation of the Alps. 

 There is abundance of direct geological evidence to prove 

 that they have been raised, at least much higher than before, 

 since the deposition and consolidation of the tertiary strata ; 

 and as it is scarcely less certain that the primary mountains 

 of Britain were raised at a much earlier period, it seems to 

 follow from their altitude and higher latitude, that the sur- 

 rounding region must have been the seat of more intense cold 

 than Switzerland, then without high mountains and situated in 

 a much warmer climate. 



Having spent a portion of the late summer in endeavouring 

 to trace the geological sequence of the schistose rocks of North 

 Wales, I have been naturally led into some high and unfre- 

 quented tracts where it seemed probable, if anywhere, that 

 evidence of glaciers would be found. I have examined many 

 of the main and lateral valleys on the east and south flanks of 

 the Snowdon group, of the Arenigs, and of the north end of 

 Berwyn chain, as well as of the moorland hills of Denbigh- 

 shire, between Cerrig y Druidion and Llanrwst; also those 

 which intersect the wild and barren hills that occupy the coun- 

 try between the great Holyhead road and Bala, and form the 

 dividing ridge between Merionethshire and Denbighshire. 

 These valleys descend from the highest mountains of North 

 "Wales, and are the troughs through which the numerous tri- 

 butaries of the Dee, the Clwyd, and the Conway, are carried 

 into the lower parts of the country. Many of them, from 

 their smooth uniform slopes and easy inclinations, seem cal- 

 culated to give rise to, and to retain those appearances which 

 glaciers usually create and leave behind them. In none of 

 them, however, have I found any features which appeared to 

 me to have been produced by glaciers ; none at least have re- 

 tained that outward form or shape which seemed to justify me 

 in referring them to such an origin. 



