Review of Recent Geological Literature. 191 
tions of the ice-sheet. Therefore it may be found by closer inspection 
of Icy cape that much englacial drift, although too small in relative 
amount to be observable from the east side of the Yahtse river, occurs 
within the ice-cliffs, such as lias become exposed on the surface by pro- 
gressing ablation. In the vicinity of the Yahtse and of Icy cape, how- 
ever, the superficial moraines of the Chaix hills are mingled with the 
less plentiful englacial drift, which latter seems to be the chief source 
of supply at the Sitkagi hluffs and thence eastward twenty-five miles 
to the Kame stream. 
Professor Russell and his parties in both expeditions braved many 
dangers and well performed their tasks of geographic and geologic ex- 
ploration. The narrative and the discussion of scientific results are 
presented in a most modest and entertaining manner. They mark a 
stage of great progress in our knowledge of the conditions of the Ice 
age. w. u. 
On Certain Astronomical Conditions favoraVU to 6-laciation. By <Jeo. F. 
Becker. Am. Jour, of Science, III, vol. xi.yiii, pp. 95-113, Aug. 1894. 
From a mathematical investigation of the effects of the unequal 
amounts of solar heat received by different portions of the earth's sur- 
face under varying astronomical conditions, the author sums up his 
results, differing widely from the well known views of the late Dr. ('roll, 
as follows: "I began this enquiry without the remotest idea as to what 
conclusion would be reached. At the end of it I feel compelled to as- 
sert that the combination of low eccentricity and high obliquity will 
promote the accumulation of glacial ice in high latitudes more 
than any other set of circumstances pertaining to the earth's orbit. h 
seems to me that the glacial age may be due to these conditionsin com- 
bination with a favorable disposition of land and water. This theoiy 
implies, or rather does not exclude, simultaneous glaciation in both 
hemispheres. It does not imply that the ice age should last only tenor 
twelve thousand years. If the conditions here suggested are correct, 
variations in the disposition of land and water may have determined 
intervals of glaciation, not necessarily the same ones in New England 
and the basin of the Mississippi; and there may have been considerable 
time differences in t he incept ion or the cessat ion of glaciation in various 
regions. It is not needful to assume thai the glaciation of the Sierra 
Nevada either began or ended synchronously with the ice age in New 
England. The date al whicha minimum of eccentricity last coincided 
with a maximum of obliquity can almost certainly be determined. 
According to Stock well, the obliquity has been diminishing for the pa si 
8,000 years, and was within 21 minutes of its maximum value at the 
beginning of thai time. According to Lcverjrier, the eccentricity passed 
through a minimum 40,000 years ago, the value being then about two- 
thirds of the present one. So far as I know, the obliquity has not been 
computed beyond 8,000. This can of course be done for Stockwell's 
value of I he masses of I lie pi a nets, or for newer or better ones. A|] i he 
indications seem to be thai within thirt\ or forty thousand years con- 
