Editorial Comtnenl. 139 
There are two lines of research that have borne evidence of 
the validity of this hypothesis, arr<l Prof. Carpenter appeals to 
both. First. There is a continually increasing amount of 
evidence that the glacial epoch was comparatively recent. He 
refers to the conclusions of Prestwich, placing it not more than 
fifteen or twentj'-five thousand years ago, terminating probably 
eight or ten thousand years ago; the late revised calculation of 
the recession of the falls of Niagara (see the Proceedings A. A. 
A. S. Buffalo meeting, 1886) as well as of that of the falls of 
St. Anthony (vol, ii, Final report of the Minnesota geological 
survey); also the results reached by Dr. Andrews in Jiis discus- 
sion of the "great lakes as chronometers of post-glacial time," 
and other data that have been employed to determine the date 
of the glacial epoi;h, conspire to bring it still nearer the present, 
and probably within the limit of ten thousand years.* Accord- 
ing to Prof. Jos. LeConte the great over-flow eruptions of the 
western part of the United States occurred at the close of the 
Miocene and this seems to have been within the human period, 
reasoning from the human remains reported by Prof. Whitney 
from beneath it in California. 
Second. Prof. Tyndall says : "Cold will not produce glaciers ; 
you may have the bitterest north-east winds without a flake of 
snow;" and again: "It is perfectly manifest that by weakening 
the sun's action, either through a defect of emission or by the 
steeping of the entire solar system in space of a low temperature, 
we should be cutting off the glaciers at their source." (Heat 
considered as a mode of motion. ) Tn sliort Tyndall has shown 
that in order to have a glacial epoch we need more heat, not 
less, that we must make our "pumping engines" do more work, 
to supply greater precipitation. Dr. Croll says ( Climate and 
Time, p. 74): "Heat to produce evaporation is just as essential 
to the accumulation of snow and ice as cold to produce conden- 
sation." Sir John Lubbock says (Prehistoric Times): "Para- 
doxical as it may seem the prevailing cause of the glacial cold 
may be after all an elevation of the temperature of the tropics," 
Prof, Jos, Henry in a communication to the Washington Phil- 
osophical Societif (Bulletins, vol, 2, pp, 35 and 37 — 1875 to 1880) 
held a similar view, and applied it to the existence of "extensive 
♦Compare also, "The life-history of Niagara." by Dr, .Julius Polilinau, in 
the Am. Intt. Mininrj Engineers. 
