LITERARY NOTICES. 



559 



riod, species from far north having been 

 driven southward by the severe climate and 

 accumulating ice, as is shown by remnants 

 of a flora and fauna like those of the arctic 

 regions, which have managed to contiuue 

 their existence since the Ice age on the tops 

 of mountains in temperate latitudes. Many 

 peculiarities in the distribution of forest 

 trees, made known by the researches of the 

 late Prof. Asa Gray, also find their' only ade- 

 quate explanation in these vicissitudes of 

 climate. 



Northwestern Europe was covered by an 

 ice-sheet about half as extensive as that of 

 our own continent, and the author gives on 

 a single map a comparative view of the gla- 

 ciated areas of both. Another map shows 

 the course of the terminal moraines recently 

 traced by Lewis in Ireland, Wales, and Eng- 

 land, and by Salisbury in Germany, each of 

 whom had much previous experience from 

 work on glacial geology in the United States. 



Treating of the cause and date of the 

 Glacial period, Prof. Wright rejects the as- 

 tronomic theory of Croll and Geikie, which 

 attributes the severe climate to conditions 

 dependent on the eccentricity of the earth's 

 orbit between two hundred and forty thou- 

 sand and eighty thousand years ago. Instead 

 of this, the post-glacial erosion of the gorge 

 below the Falls of Niagara and of that ex- 

 tending eight miles on the Mississippi from 

 Fort Snelling to the Falls of St. Anthony at 

 Minneapolis, similar erosion by streams trib- 

 utary to Lake Erie, changes in the shores 

 and deposits of dune sand about Lake Michi- 

 gan, and other observations, afford much 

 shorter measures of the time since the de- 

 parture of the ice-sheet, agreeing in their 

 testimony that it was no longer ago than 

 seven to ten thousand years. Prof. Wright 

 is also disposed to doubt that there have 

 been two distinct Glacial epochs in America, 

 and believes that the facts thus far obtained 

 are capable of explanation on the theory of 

 but one epoch, with the natural oscillations 

 accompanying the retreat of so vast an ice- 

 front. 



The last two chapters review the evi- 

 dences of man's presence in America and 

 Europe during the Glacial period, specially 

 describing the important discoveries of pa- 

 laeolithic implements in glacial gravel depos- 

 its near Trenton, N. J., by Abbott; near 



Claymont, Del., by Cresson ; in the Little 

 Miami Valley, Ohio, by Metz ; and at Little 

 Falls, Minn., by Miss Babbitt. But doubts 

 remain concerning the authenticity of the 

 famous Calaveras skull and stone imple- 

 ments denoting a higher state of develop- 

 ment than that of palaeolithic man, reported 

 as occurring in the lava-covered gold-bear- 

 ing gravels of California, which, if obtained 

 there in the undisturbed gravel, would give 

 to our race a considerably greater antiquity 

 than is otherwise known. 



In the appendix Mr. Upham contributes 

 " an explanation of the causes of the Glacial 

 period, which, in this application of its fun- 

 damental principle, seems to be new, while 

 in its secondary elements it combines many 

 of the features of the explanations proposed 

 by Lyell and Dana and by Croll. Briefly 

 stated, the condition and. relation of the 

 earth's crust and interior appear to be such 

 that they produce, in connection with con- 

 traction of the earth's mass, depressions and 

 uplifts of extensive areas, some of which have 

 been raised to heights where their precipita- 

 tion of moisture throughout the year was 

 almost wholly snow, gradually forming thick 

 ice-sheets ; but under the heavy load of ice 

 subsidence ensued, with correlative uplift of 

 other portions of the earth's crust ; so that 

 glacial conditions may have prevailed alter- 

 nately in the northern and southern hemi- 

 spheres, or in North America and Europe, 

 and may have been repeated after warm in- 

 terglacial epochs." Mr. Upham believes that 

 the earth's crust floats in a condition of hy- 

 drostatic equilibrium upon the heavier liquid 

 or viscous mobile interior, or layer envelop- 

 ing the interior, subject, however, to strains 

 and resulting deformation because of the 

 earth's contraction. But such oscillations 

 seem not inconsistent with the doctrine that 

 the earth's interior is solid, with a degree of 

 mobility like that of ice in glaciers. Whether 

 the formation of the Himalayan mountain- 

 range has been contemporaneous and correl- 

 ative with the Glacial period, and the Appa- 

 lachian uplift with the Carboniferous and 

 Permian glaciation of portions of the East- 

 ern hemisphere, as is here suggested, must 

 probably require many future years of ob- 

 servation and study to determine. 



All who have read the earlier work of 

 Prof. Geikie, or listened to Prof. Wright's 



