102 THE AMERICAN NATURALIST. [VoL. XXXV. 
they extended southward, following them in their retreat to the 
north, receiving and distributing the ice floes and icebergs with 
their deposits in various places according to the varying con- 
ditions, such as changes in currents and winds and the oscil- 
lations of the rise and fall of the earth’s crust. A sea like that, 
shut out from connection with the Atlantic Ocean to the west, 
only connecting with the Arctic Sea to the north, and fed by 
the melting ice and snow of the surrounding countries, would 
present features something between the Baltic and Hudson 
Bay. Its waters would naturally be brackish, and conse- 
quently deficient in marine life, except in a few favorable 
localities. The supposition of such a sea would meet all the 
requirements the biologists can put to it; it would explain the 
varied conditions of the boulder clay and the presence as well 
as the scarcity of the distinctly marine deposits. It would 
also meet their demand for an effective barrier north of the 
Caspian Sea to the invasion of Siberian forms during the 
earlier part of the glacial period, as a combination of glacier 
and sea is as effective for this purpose as either of these 
agents alone. On the other hand, it certainly cannot be taken 
as an indication of a mild climate, possibly milder than our 
present one. 
While I have thus been unable to accept one of Dr. Scharff's 
more general and fundamental propositions, viz., the one which 
relates to the glacial climate, there is another of his more special 
conclusions from which I must also dissent, vzz., the northern 
origin of the invasion, which he styles the Arctic migration. 
As already explained above, Dr. Scharff accounts for the 
presence of certain Arctic animals in Ireland, Scotland, and 
other parts of western Europe, including the Alps and the 
Pyrenean peninsula, by a supposed immigration from America, 
via à continuous land connection between Greenland, Spits- 
bergen, Norway, Great Britain and Ireland, and France, this 
immigration being only subsequent in age to the Lusitanian 
fauna, and distinctly older than the Siberian immigration, which 
came to Europe much later from the east, though also consist- 
Ing, to a great extent, of northern types closely allied to those 
composing the Arctic invasion. 
