EdiforidI Comuient. 255 
ruary. Like Woeikof and others, lie finds this theoiy insuf- 
ficient to account for the climatic conditions of the Glacial 
period and the accumulation of its continental ice-sheets. 
This conclusion, however, seems not to be inconsistent with 
the view presented in the last number of the American Geol- 
oiiisT (page 201), that the Kansan and lovvan stages of ex- 
tended growth of the North American ice-sheet, with the 
intervening considerable retreat of the ice border in the 
upper part of the Mississippi basin, were due to the last two 
cycles in the precession of the equinoxes, bringing the winters 
of the northern hemisphere in aphelion. Dr. G. F. Becker's 
recent investigation of astronomic conditions favorable to 
glaciation lead him to conclude, altogether differently from 
the three British scientists first mentioned, that low eccen- 
tricity of the earth's orbit and high obliquity of the ecliptic 
are likely to promote snow and ice accumulation in high lati- 
tudes and mountain districts.* He thinks also that geographic 
conditions, as high land elevation and changes of niairine 
currents, conduced toward the causation of the Glacial period. 
Granting that the Pleistocene ice-sheets were formed, as Dr. 
Becker indicates, by such concurrent geographic and astro- 
nomic conditions within the past 50,000 years, continuing 
until some 8,000 years ago, it seems to me highly probable 
that even the small present eccentricity (0.0168) was adequate 
to cause the interglacial recession of the ice-sheet in the in- 
terior portion of our continent between the Kansan and lowan 
glacial stages, of which we have abundant evidence in buried 
forests, peat, and other fossiliferous beds enclosed between 
deposits of till in Ohio and the other states west and north- 
west to Minnesota. When we compare even this small ratio 
of eccentricit}^ with the great range from the earth's mean 
surface temperature, produced entirely by the sun's heat, to 
the absolute zero, which Dewar finds to be — 461° Fahrenheitf 
(this being the temperature, or rather the total absence of 
heat, in the interstellar spaces and upon the earth if its sup- 
ply from the sun should cease), w-e ma}' believe that so slight 
climatic effects as might result from the present eccentricity, 
in connection with equinoctial precession and nutation,'coukl 
*Am. Jour, Sci., Ill, vol xi.viii, pp. y.VlU}, An-,'., 1804. 
fMcClure's Muj^a/iiif. vol. in, pp. ooT-.lO".*, Nov.. lS!i4. 
