CH. V] PALAEOZOIC GLACIAL PERIODS. 233 



snow and ice and to prevent the influx of warm currents 

 from more southern latitudes. The undoubted boulders 

 he regards not as evidence of exceptional glaciation, but 

 as evidence of high mountains with glaciers which carry 

 down these boulders ; this is not inconsistent with a warm, 

 even tropical, temperature at their base. It is not until 

 we reach the Permian period that Mr Wallace thinks that 

 a severe glaciation occurred. In the west of England 

 there are beds of ice-borne rocks which must have been 

 carried for a distance of fifty miles and this together with 

 the poverty of the fauna and flora are indications of a 

 glacial period. If however we consider as Prof. Huxley 

 did in 1870 that even the highest group of animals the 

 mammalia probably originated well within the Palaeozoic 

 period, since it has taken from the commencement of the 

 Eocene to almost to-day for so small a modification as the 

 reduction of the horse's foot from the five-toed to the 

 one-toed condition, even this remotely distant glacial 

 epoch will be sufficiently near to exclude all possibility 

 of the polar origin of mammalian, let alone all other 

 vertebrate and invertebrate life. We may take it therefore 

 that the polar regions enjoyed a mild or even a warm 

 climate throughout the tertiary and secondary epochs, 

 but it has been pointed out that in Carboniferous and 

 Silurian times the temperature judging from the fauna 

 and flora was of the same kind; this however is of no 

 importance from the present point of view if the Permian 

 glacial period really took place as the evidence seems to 

 assert. 



