regions were inaccessible ami harred the many attempts of great explorers who strove without 

 success to cross the passages leading from north-east to north-west. Before this icy invasion, 

 another warming up of the Arctic in 1200 A. D. opened the northern seas and made possible the 

 tremendous extension of the Vikings' empire, from Scandinavia to the American coasts. We 

 are at the dawn of a similar period, for the ice is receding on all sides. The famous passages 

 are unblocked. In three months a Russian ice-breaker made the crossing that took Nordenskjold 

 three years from 1876. The (Canadian Archipelago is open. North of Europe, Spitzbergen, 

 Novaya Zemlya and the Franz Josef Archij)elago can be rounded by ships of a greater tonnage 

 than those I remember seeing 40 years ago, surrounded by pack-ice e\en in the summer. The 

 west coast of Greenland is open, the continental glaciers are receding and soon the great polar 

 shield will become once more the " greenland " with fields, much as it was when Eric the Bed 

 disco\ered it in 982 A. D. The skies over the pole have become aerial highways and aeroplanes 

 look down on broken-up ice-fields. Slowly drifting in the open sea are immense islands of ice, 

 some of which may even carry the camps of courageous explorer-scientists. 



More and more each year, animal life is moving back to the north. Even in winter there 

 is scarcely any recession of the extreme waters of the transgressions, which bring with them to 

 high latitudes species that never ventured there before. Trawlers work round Bear Island as 

 easily as in the North Sea and go after the cod into the Barents Sea. Here dolphins ()lay at the 

 surface and pursue the herring, which meet in the White Sea a local race of Pacific herring 

 (C.lupcii pdllasii). A long time ago, when the Arctic was warming up, these fishes ranged along 

 the entire Siberian coast, but caught unawares by a barrier of ice, they have remained ever 

 since confined to the nort h of Russia. The conditions which presided over this ancient migration 

 are being reprodnicetl at the present time. 



The glacial adventures of the salmon. 



Altiiough tiie salmonids ha\e many features in common with the older bony fishes which 

 were evolving in the Secondary Period (in Upper Oetaceous times) it seems that the family 

 must be of recent origin. No fossils have been fount! earlier than the end of the Tertiary Period. 

 Living in the deej) sea are the related argentines also provided with a small adipose dorsal fin 

 set in front of the tail — fishes which doubtless typify the ancestors of salmon. These large- 

 eyed, bathydemersal animals found suitable living conditions in the cold waters of the north 

 polar regions and evolved into anadromous fishes. 



The great glacial period of Pliocene times was particularly propitious for the development 

 and dispersal of the salmonid fishes. Then the ice-cap covered the northern lands, while the 

 pack-ice blockaded the North American coast as far as (lape Hatteras and extended down to 

 the British Isles. Great glaciers overlaid Scandinavia and the northern parts of Russia, Siberia 

 and (lanada. Greenland. TcelaTid and all the [tolar islands fiarely enu^rged from this gigantic 

 covering of ice. 



When climatic conditions changed, the ice began to melt and a vast quantity of fresh water 

 spread over the surface of the northern seas. Great rivers which of)ened into the Arctic Ocean 

 fiowcd freely, at least in the summer time, and there was really little dilTerence in salinity between 

 river and marine waters. So the salmon readily formed the habit of going from the sea to the 

 rivers to spawn; thereafter to return to the coastal zone to feed. The Baltic, the North Sea 

 and the Irish Sea were still immense glacial valleys, while very diluted waters from the polar 

 retrions even washed the shores of southern iMirope. In the Mediterranean the melting of the 

 glaciers of the Alps, A|)eimines and the Balkan and Atlas mountains lowered the salt content 

 of the surface layers. 



For salmon this was a |>arlicularly faMiurabIc period. Lea\ing high latitudes, they grad- 

 ually moved southwards and took to fre(]uenting all the great European ri\ers — not oidy the 

 Atlantic tributaries but also the Ebro, the Rhone, the Po and the Algerian rivers. Much the 

 same thing occurred im the coasts of North America and along southern Asia as far as Korea. 



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