Canon Tristram on the Polar Origin of Life. 205 



tical with the Miocene flora of Spitsbergen, Novaya Zemlya, 

 Grinnel Land, Melville Island, the Parry Islands, Bering^s 

 Straits, and Greenland, was iu time incalculably posterior 

 to it. By still greater intervals must the strata nearer the 

 equator be separated from similar Polar deposits. 



Geologists are agreed that in the Miocene period the 

 North Polar region was a continental area, supporting 

 throughout its extent the same or similar forms of life, as 

 evidenced by the remains found in the districts named above, 

 which may be looked on as the relics of that submerged 

 continent. Here life was generally diffused, and, judging 

 from the fossil plants — the Magnolias, Sequoias, and the 

 like — the temperature was that of the present equatorial 

 zone. During the secular refrigeration of the earth the 

 temperature of this continent gradually decreased till it 

 became wholly incapable of supporting such life as we now 

 find in the torrid and temj)erate zones. There were only 

 two routes of exit for the retreating aquatic and littoral 

 forms : the openings of the North Atlantic and North Pacific 

 Oceans, between Greenland and Scandinavia, and between 

 Kamschatka and the Rocky Mountains. Down these four 

 lines the fauna and flora of every kind steadily, but reluc- 

 tantly, retired in slow succession, progressing no faster than 

 the modification of the climate demanded. The further they 

 proceeded southwards, the more isolated they became from 

 those which had taken a different route. The law of isola- 

 tion produced its invariable result, unchecked by that inter- 

 breeding which might have arrested departure from the 

 original type. The more sedentary the species, the more 

 marked became the divergence. Those species which were 

 the first to leave — the ancestors of the present tropical inha- 

 bitants — became the most differentiated. Those Avhich were 

 the last to leave, and which most persistently revisited their 

 ancestral homes, there associated with their kinsfolk from 

 east and west, and thus preserved the original type through- 

 out the world ; as we see in the case of the Knot, the Sander- 

 ling, the Turnstone, and many other Waders, which breed 

 generally throughout the Arctic circle. The Gulls, on the 



