838 



SCIENCE. 



[N. S. Vol. XII. No. 309. 



That there is reason to modify the for- 

 merly current assumption that extremely low 

 temperatures existed in the Northern Hem- 

 isphere during the Glacial Epoch is now 

 urged by not a few authorities.* In a paper 

 which advocates revision of preconceived 

 ideas on this point, Vater f calculates that 

 points in middle Germany which were not 

 distant from the edge of the great Ice 

 Sheet, possessed, during the Glacial Epoch, 

 a mean annual temperature of 4° C, as 

 compared with 10.6° C. at the present day. 

 But even this amount of difference iQUst 

 have wrought great changes in the vegeta- 

 tion, and, if the same ratio obtained in 

 eastern North America, we may well assume 

 that no member of what constitutes to-day 

 the characteristic Austro-riparian flora 

 could have maintained itself in the Appa- 

 lacliian region, during the climax of the 



* Thus 3. D. Whitney, who goes much farther than 

 most geologists in reaction against previously enter- 

 tained ideas as to the extent and importance ot the 

 Ice Sheet, remarks as follows in his well known paper 

 on ' The Climatic Changes of Later Geological Times ' 

 (Contr. to Amer. Geology, Harvard University, Vol. 

 2, p. 268, 1888) : "A general refrigeration of the 

 earth could never have caused that peculiar distribu- 

 tion of snow and ice to which the term Glacial Epoch is 

 commonly applied ; and* * * the phenomena in ques- 

 tion are entirely compatible with a higher mean tem- 

 perature than now prevails." Again (p. 321): "We 

 have no right to assume as having existed during the 

 Glacial Epoch a period of intense cold, or even a 

 lower mean temperature than that now prevailing 

 over the earth." And (p. 387) : " It is possible to 

 lay aside all idea of explaining the phenomena of the so- 

 called Glacial Epoch, by referring them to the exten- 

 sion of a general or Polar ice-cap over the land of the 

 Northern Hemisphere. * * * The entire body of facts 

 presented brings out most clearly the true condition 

 of things, namely that the Glacial Epoch was a local 

 phenomenon, during the occurrence of which much 

 the larger part of the land-masses of the globe re- 

 mained climatologically entirely unaffected." This 

 author represents, however, an extreme view, which 

 is rejected by many geologists. 



t ' Das Klima der Eiszeit ' ; Sitzungsber. d. na- 

 turw. Gesellsch. Isis in Dresden, 1883, pp. 56, 57 

 (1884). 



Ice Age.* For we must remember that the 

 great glacier made its way southward as far 

 as the present location of Cincinnati, on 

 the Ohio Eiver, and extended to the south- 

 ern shore of Staten Island. f 



We may premise, therefore, with consid- 

 erable confidence, that any portion of the 

 Lower Austral flora of to-day which may 

 have inhabited the Appalachian region 

 prior to the Pleistocene retreated to lower 

 altitudes and latitudes when the Ice Sheet 

 approached its most southern limit. If we 

 were to maintain, on the other hand, that 

 Lower Austral plants had survived the 

 Glacial Epoch in the Appalachian region, 

 we should be compelled to assume that 

 species which had developed under the mild 

 climatic conditions generally believed to 

 have prevailed, even in high northern lati- 

 tudes, during Miocene and Pliocene times, 

 later adapted themselves to the considera- 

 bly lower temperatures prevailing during 

 the comparatively brief Glacial Epoch, 

 and, after the close of that Epoch, read- 

 justed themselves to the warmer tempera- 

 tures which again held sway. J 



* A. C. Seward, in discussing ' Fossil Plants as 

 Tests of Climate' (London, 1892), p. 50, after sum- 

 ming up the evidence pro and con which has been 

 brought forward to prove that forests could have 

 maintained themselves amid or very near the great 

 glacier, decides against the possibility of such sur- 

 vival. On the other hand, we have no right to as-^ 

 sume that a vigorous forest growth may not have con- 

 tinued to flourish in the greater part of the Appa- 

 lachian region, at least at low elevations, throughout 

 the Glacial Epoch. For, as the same author re- 

 marks, pines and even tree ferns thrive to-day at the 

 very edge of the terminal moraines of New .Zealand 

 glaciers ; while, in Alaska, some glaciers (notably the 

 Malaspina) are largely covered with spruce, alder and 

 other trees. 



t The area supposed to have been covered by the 

 Ice Sheet in North America has been mapped by Pro- 

 fessor T. C. Chamberlin ; 7th Ann. Rep. U. S. Geol. 

 Survey, pi. 8 (1888). 



t It will be obj ected that it is not always safe to 

 argue from the present requirements of organisms 

 (especially of genera and still larger groups), the 



