296 Searles V. Wood—The Cause of the Glacial Period. 
the Arctic circle on the Greenland side of the pole must come from 
the water of the Gulf Stream itself, or from water which is kept un- 
frozen by the influence of this stream. This part is a strip of sea 
stretching further and further away from Greenland as it extends 
north-eastwards to Spitzbergen, so that, while the sea is almost per- 
manently ice-covered off Hast Greenland, on the eastern coast of 
Spitzbergen navigation is open during several months to within 
fifteen, and for some time to within ten, degrees of latitude from the 
Pole. In the Southern Hemisphere the enormous disproportion of 
sea to land compensates for the absence of so decided an influx of 
warmer water from lower latitudes, while the vast expanse of the 
sea keeps it more open, proportionately to the greater distance 
equatorwards in which land-ice reaching the sea occurs in that 
hemisphere (which is 16° of latitude on the equator side of the 
Antarctic circle, or 10° more than is the case in the northern), and 
so furnishes the snow that makes that land-ice. 
A diminution of the sun’s heat would diminish the total amount 
of vapour over the world, necessarily ; yet since the area where this 
vapour is precipitated as snow would be proportionately extended, 
the total amount of snowfall might not be lessened, the deficiency in 
precipitation taking place only as rain; so that even if as great a 
snowfall as now occurs were necessary to explain the phenomena of 
the Glacial Period, there might yet have been snow enough to give rise 
to all these phenomena, especially if those regions which now receive 
the principal part of the snow then received less than they now do. 
The case, however, when examined by the light afforded by the 
past glaciation and existing precipitation of the United States, as 
compared with the existing glaciation and precipitation of Greenland, 
goes much further than this, and appears to me to bear out the pro- 
position I now venture to put forward; which is that the stupendous 
mass of land-ice under which the basin of the St. Lawrence, and 
parts adjacent thereto (7.e. the glaciated area of Hastern North 
America,) were buried may have accumulated under a precipitation 
less than that which now takes place in the same region. But 
first let me explain how the phenomena of the North American 
glaciation are connected with the precipitation of that country. 
Jas. D. Dana has shown, by reference to Schott’s memoir on the 
Precipitation of Rain and Snow in the United States, that the 
glaciation of the eastern side of North America, and the presence of 
the great unglaciated region of the central part of that continent, is 
intimately connected with the present relative precipitation of the 
respective areas, and is proportional thereto.’ The cauldron in which 
is brewed the rain which falls on the eastern side of the United 
States is, as Asa Gray observes,” the Gulf of Mexico. The great 
ocean current originating under the equator in mid-Atlantic, and 
which Croll in his hypothesis contends did not when aphelion 
occurred in mid-winter of the Northern Hemisphere enter the Gulf 
1 Amer. Journ. of Science, third series, vol. ix. p. 312; vol. x. p. 885; vol. xiii. 
p- 80; and vol. xvi. p. 240. 
* Same Journal, vol. xvl. p. 88. Hisremarks are in reference to the forest growth, 
and not to the glaciation. 
