Canon Tristram on the Polar Origin of Life. 207 



limits the extension of the ice-age in Europe to the nortli 

 and central portions as far as Sa ony^ the Alps, and Pyrenees ; 

 and in America to Canada and the eastern States as far as 

 the 39tli parallel of north latitude. Nordenskiold, in the 

 " Voyage of the ' Vega ' ," repeatedly remarks upon the evi- 

 dence which Siberia affords that it has not been subject to 

 any great geographical changes since the Jurassic period 

 (vol. ii. p. 209; &c.), and he writes of the shores of the Arctic 

 Ocean : — " It is certain that the ice-cap did not extend over 

 the plains of Siberia, where it can be proved that no ice-age, 

 in a Scandinavian sense, ever existed, and where the state 

 of the land from the Jurassic period onwards was indeed 

 subjected to some changes, but to none of the thoroughgoing 

 mundane revolutions which in former times geologists loved 

 to depict in so bright colours. At least the direction of the 

 rivers appear to have been unchanged since then. Perhaps 

 even the difference between the Siberia where Chikanovski's 

 Ginko woods grew and the mammoth roamed about, and 

 that where now, at a limited depth under the surface, con- 

 stantly frozen ground is to be met with, depends merely on 

 the isothermal lines having sunk slightly towards the equator " 

 (vol. ii. p. 246). All the evidence tending to show the limited 

 area of the glacial epoch proves, — first, that we have no need 

 to invoke changes connected with the eccentricity of the 

 earth's orbit, for then the extension of the ice-clad region 

 would have been circum polar, instead of being grouped 

 rovmd the North Atlantic ; secondly, that we need not 

 invoke the glacial epoch at all, still less an indefinite number 

 of glacial epochs, to account for the present phenomena of 

 distribution and migration, for then the solution would apply 

 only to the Atlantic distribution; while, dismissing these 

 disorderly interruptions, the secular refrigeration of the globe 

 sufhees for all. 



Confining myself, as in the pages of ' The Ibis ' I am 

 bound to do, to the avifauna exclusively, and abstaining 

 from the attractive illustrations of the subject afforded by 

 the MoUusca, and still more by the Flora, I would A^enture to 

 sugest that the gradual refrigeration is sufficient of itself to 



