HVPOTHESIS OF CAUSE OF GLACIAL PERIODS ~*~ 755 
longitude 95° west. This channel is always tightly jammed with 
ice pressed in from the northwest. So persistent and strenuous is 
the pressure of this ice-pack that it constitutes an effectual barrier 
to the northwest passage, and has thus far mocked all attempt to 
force it. This implies a definite and persistent movement from 
the northwest to the southeast. 
It appears, then, that from far east of Greenland to the west- 
ern limits of the northern archipelago there is a definite con- 
vergence of the ice currents toward a point located somewhere 
north of Hudson Bay, 7. e¢.,a point lying to the north of the 
two great centers of Pleistocene glaciation, the Labradorean and 
the Keewatin, and on a meridian that runs between them. 
It is interesting to note that the point of convergence lies in 
the general vicinity of the magnetic pole. and this: obviously 
leads to the further suggestion that there may be some genetic 
connection between the two as yet undetermined. 
Concurrent in import with this is the fact that on the opposite 
side of the north pole the coasts of northern Asia and Europe 
become partially free of ice each season. This, although doubt- 
less partly due to the effects of the fresh water borne in by 
the great rivers of those coasts, is probably none the less an 
expression of the fact that the polar ice is not crowded down 
upon those coasts; for if it were, its great mass would com- 
pletely overwhelm the effects of even the great Siberian rivers. 
This phenomenon, taken in connection with the direct observa- 
tions of the ice-drift made by De Long, Nansen, and others, 
leaves little room for doubt that the great polar ice-field drifts 
away from the Eurasian coast and crowds toward Hudson Bay. 
The meridian of 90° may be taken as rudely representing the 
axis of this converging ice-drift. It is interesting to note that 
this same meridian bisects the Mississippi valley and crosses the 
southern apex of the great American glacial field. 
Listribution of arid zone.— Correlated with this remarkable 
phenomenon is an equally remarkable distribution of the great 
desert tracts of the eastern hemisphere. Commencing on the 
Atlantic coast of Africa between 10° and 30° north latitude, the 
