LIFE ON THE EARTH. 151 



British and Scottish mountains, and that the remark- 

 able conglomerate of the Malvern and Abberley hills, 

 now supposed to be of Permian age, is due to the 

 floating and stranding of icebergs along the edge of 

 the sea which washed the Longmynd, Abberley, and 

 Malvern hills 1 ; and a more comprehensive conjecture 

 was once proposed by Agassiz, that the ancient cli- 

 mate was subject to several sudden depressions, 

 coincident with great destructions of life, followed by 

 some rise of temperature, and a renewal of life. 



Admitting that such great changes have happened 

 in the climate of our north temperate zones, how are 

 they to be accounted for? 



If in agreement with the conclusions of Herschel 2 

 we admit the earth's orbit to be only in a small 

 degree variable, and so the sun's influence nearly 

 constant; and decline to accept the hypothesis of 

 Poisson 3 that the solar system in its wandering 

 through space has encountered various temperatures ; 

 we shall find our power of explaining the great dif- 

 ferences of climate, on the same area in ancient and 

 modern times, reduced to estimating the effect of 

 variations proper to the planet. It has been sup- 



1 See Memoirs of the Geological Survey, n. 1 for my descrip- 

 tion of this conglomerate. Professor Ramsay is the author of the 

 hypothesis referred to. 



2 Geological Transactions, Ser. 2, Vol. n. 



3 Whewell in Reports of British Association, 1835. 



