Land-bridge from Northern Europe to North America. 29 
that the reindeer had probably utilized this land-connexion in gaining 
access to Europe from its supposed American centre of dispersion. 
Further studies have led to the conviction that a second and more 
southerly land-connexion, joining Scotland, Iceland, and Greenland 
with America, must have existed in later Tertiary times. This does 
not materially alter the general principle of his original views; and 
he still adheres to the belief in a North Atlantic land-bridge between 
Europe and America during the lifetime of the reindeer. 
In 1897 Mr. W. S. Green gave us the results of his expedition to 
the Rockall Bank. Surrounded by deep water on all sides, this bank 
is of an average depth of 100 fathoms, and hes far out in the Atlantic 
to the west of Scotland. Dredging on the bank yielded only such 
shallow-water species of molluses and other marine invertebrates as 
could not have lived there under the present conditions. Moreover, 
as all the specimens were dead, it was concluded that the bank had 
only subsided to its present depth within comparatively recent times.’ 
In 1900 the Danish ‘ Ingolf’ expedition to Iceland likewise reported 
_having met littoral molluscs near the island at considerable depths 
where these animals could not possibly have lived. That such cases 
as these are due to accidental dispersal by floating icebergs containing 
shells in the ice-foot or by floating seaweeds, had been suggested ; but 
the view that the occurrence of shore forms of animal life in deep 
water implies a depression of the land seems to meet with more 
general favour, especially as no icebergs are known to stray to the 
Rockall Bank at present. 
More recently Professor Hull lays stress on the occurrence of 
channels in submerged platforms bordering the British Isles, and 
urges that they represent the drowned river-valleys and canons of an 
ancient land-surface. By means of the Admiralty charts he succeeded 
in tracing the course of the River Shannon for a hundred miles 
beyond its present mouth, right to the edge of the continental plat- 
form, while he followed the continuation of the River Erne for 
a distance of 80 miles from the Irish coast.’ 
In America similar researches have been conducted, chiefly by 
Dr. Spencer,’ but while Professor Hull advocates an elevation of the 
land during the early part of the Glacial period of 7000 to 8000 feet, 
Dr. Spencer suggests an uplift of 12,000 to 15,000 feet. A more 
cautious attitude on these oceanographic problems was adopted by 
Mr. Hudleston. He conceded that some sort of a bridge across the 
Atlantic may have existed during portions of the Tertiary era; but he 
did not believe in'an uplift beyond 2000 or 3000 feet.* 
The subject of continental shelves has lately received renewed 
attention from Dr. Nansen, and is discussed by him at great length. 
At several places, he argues, there is weighty evidence for the sup- 
position that the drowned river-valleys have been sculptured atter the 
1 W. S. Green, ‘‘ Notes on Rockall Island’”’: Trans. Roy. Irish Acad., 1897, xxxi. 
2 K. Hull, ‘‘Submerged Terraces and River Valleys’’: Trans. Vict. Inst., 1897, xxx. 
3 J. W. Spencer, ‘‘ Submarine Valleys”: Bull. Geol. Soc. America, 1903, xiv, 
p. 224. 
4 W. H. Hudleston, “‘ Eastern Margin of North Atlantic Basin’’: Gzox. Mac., 
1899, p. 148. 
