340 APPENDIX. No. XV. 



leaf-beds of Mull in the American tertiari.es ; and he suggests 

 that the temperate flora, which drove the warmer Eocene flora 

 to the south and east of Europe, travelled by way of Green- 

 land, Iceland, and the Hebrides. 



In Miocene times the climate of Greenland and Alaska 

 was that of New York and St. Louis, while, in the succeeding 

 glacial era, the climate now existing in Greenland came 

 down to the latitude of New York, a cold temperate climate 

 prevailed in Mexico, into which the advancing cold forced 

 the herds of mammals which covered the plains of North 

 America, where they were nearly all exterminated. 



Glaciation. — During the thaw produced by the short 

 episode of warmth that represents in the Arctic regions the 

 summer of other lands, sub-aerial denudation of the surface 

 of the cliffs takes place on a gigantic scale, vast masses of 

 rock fall from the cliffs, and form a talus concealing their 

 base, like the ' screes ' of the English Lake District. 



On the close of the transient summer the rocks are satu- 

 rated with moisture, cleaved slate cliffs and the loose material 

 forming the ' screes ' being alike charged with water to their 

 utmost capacity ; without any warning or gradual approach 

 winter conditions appear, and the face of nature is changed 

 in a few hours ; moisture and running water are converted 

 into ice, which in process of expansion exercise a destructive 

 force on the rocks which is hardly comparable with the sub- 

 aerial denudation going on in more temperate climes ; and on 

 the first appearance of thaw, masses of rock, separating along 

 lines of weakness formed by planes of jointing and bedding, 

 are detached from the cliff, and falling on the snow-covered 

 6 screes ' slide down to the ice-foot beneath, the impetus being 

 often sufficient to carry them on to the floe, where they 

 remain until they are carried seaward on the general break-up 

 of the ice. 



The ice-foot is built up not so much by the act of freezing 

 of the sea-water in contact with the coast, as by the accumu- 

 lation of the autumn snow-fall, which drifting to the beach is 

 met by the sea-water at a temperature below the freezing point 



