RECENT ADVANCES IN GEOLOGY. 411 
amount of the earth's eccentricity for the period of three 
millions of years, at intervals of 10,000 years for a greater 
portion of that time, and 50,000 years for the remainder. 
He infers that a glacial period occurs when the eccentricity 
of the earth's orbit is at a maximum, and the solstices fall 
when the earth is Zn perihelio and in aphelio; and that only 
one hemisphere has a glacial climate at the same time, which 
occurs when the winter is in aphelio. 
In this connection, I may mention the labors of our own 
countryman, Mr. Stockwell, who has prepared a paper, now 
on file in the Smithsonian Institution, embodying his own 
calculations as to the earth’s eccentricity for the past two 
millions of years. 
There is such an intimate connection between the several 
branches of science that the researches in one field often 
throw light upon the obscure points in another. In the solu- 
tion of this difficult problem, the geologist may invoke, and 
I trust not unsuccessfully, the aid of the astronomer. 
That a set of causes were active during the Drift Epoch, 
in one hemisphere, which remained dormant in the other, 
admits of little doubt; and the advocates of the astronomi- 
cal theory, as evidences of the shifting of vast amounts of 
water from one pole to the other, point to the marked differ- 
ences in the topographical features of the two hemispheres. 
In the Austral region we meet with projecting headlands 
and peninsula-like terminations of continents, and groups 
and chains of islands in the Pacific and Indian oceans ex- 
tending over vast areas, which rise up like the peaks and 
crests of mountains. These are the evidences of a gradu- 
ally engulfed hemisphere. In the Boreal region we have 
wide expanses of land diversified by mountains, prairies, and 
plains; elevated sea-beaches and river-terraces, most con- 
Spicuously displayed on the borders of the Arctic Sea; vast 
Oceanic shoals; a marine fauna of a northern type preserved 
in beds of 1,400 feet, and stratified beds of gravel and sand 
2,000 feet, above the ocean-level; clusters of lakes yet re- 
