FOSSJL MAN. 



617 



geologists subdivide, beginning with the earliest, into Pleisto- 

 cene, Glacial, and Recent. 



The most important features of the Post-Pliocene or Quater- 

 nary period are : First, the advent of man and contemporaneous 

 flora and fauna. Second, the great Glacial period the period when 

 the glaciers extended over 

 the greater part of Europe 

 and North America, as at- 

 tested by the drift forma- 

 tion with its immense bowl- 

 ders torn from mountain 

 sides and carried a hun- 

 dred miles or more ; glacial 

 scratches grooves made 

 by the rocks carried by the 

 glaciers on the surfaces 

 upon which they moved; 

 terminal and lateral mo- 

 raines, heaps of rocks left 

 by the melting ice marking 

 the limits of the glaciers. 

 This Glacial epoch sepa- 

 rates the Post-Pliocene in- 

 to the three divisions men- 

 tioned before, which may 

 be called Preglacial, Gla- 

 cial, and Post-glacial, in- 

 stead of Pleistocene, Gla- 

 cial, and Recent. 



It will, perhaps, be of 

 interest to briefly indicate 

 some of the hypotheses 

 that have been advanced 

 to account for this Glacial 

 epoch. In the first place, 

 any hypothesis, in order to 



satisfy the necessities of the proposition, must include two seem- 

 ingly opposed conditions and explain their interaction. To form 

 a glacier, both heat and cold are necessary ; to form an ice mass, 

 there must be something to be frozen ; therefore there must exist 

 sufficient heat to vaporize water, charging the atmosphere with 

 aqueous vapor, which when carried to higher altitudes or sub- 

 jected to cold is condensed and precipitated in the form of snow, 

 the accumulation of which forms the glaciers. Hence, in a glacial 

 region, if the mean temperature is comparatively high, the snow- 

 fall must be great, otherwise the heat would melt the snow faster 



VOL. XLIV. 47 



FIG. 1. THE SKULL FROM THE NEANDERTHAL CAV- 

 ERN. A, side; B, front; and C, top view. The 

 outlines from camera lucida drawings, one half 

 the natural size, by Mr. Busk ; the details from 

 the cast and from Dr. Fuhlrott's photographs, 

 a, glabella; &, occipital protuberance; d, lamb- 

 doidal suture. (From Huxley's Man's Place in 

 Nature.) 



