412 



SCIENCE. 



[N. S. Vol. I. No. 15. 



berlin. The facts correspond in a general 

 way with those described by Professor Gei- 

 kie in Europe. The attempt is made to 

 group the stages of glaciation and deglacia- 

 tion both on a two-fold and a three-fold ba- 

 sis, without deciding which is the more ac- 

 ceptable. The foundation of the grouping 

 is what is called ' imbrication ' of the till, 

 or the superposition of the later or more 

 northern sheets upon the earlier or more 

 southern ones. The oldest is the Kansan, 

 next the East Ioivan,a,nd thirdly the East Wis- 

 consin stage of glaciation, followed by six, 

 seven or more terminal moraines. Professor 

 Geikie says that these general conclusions 

 harmonize with the results obtained in Eu- 

 rope, and without hesitation he correlates 

 the Kansan stage with his second glacial 

 epoch, the time of maximum, glaciation, 

 after which the ice sheets declined in im- 

 portance. 



Granting the correctness of the corre- 

 spondence of the Kansan stage to the sec- 

 ond or maximum glacial epoch of Geikie, 

 American geologists can easily complete the 

 correlation. The Lafayette or Orange sand 

 deposit will correspond to the first or Plio- 

 cene phase of the glacial epoch. This refer- 

 ence will be satisfactory to those who be- 

 lieve in elevation as a prime cause of re- 

 frigeration, as it is generally conceded that 

 the late Pliocene was a time of continental 

 uplift. It should be satisfactory to the ad- 

 vocates of the unity or continuity of the 

 ice-age, because there was just one pe- 

 riod of maximum intensity or culmination 

 of refrigeration — the Kansan phase. It 

 was preceded by the Pliocene-Lafayette 

 flood, and followed by the gradually less 

 intense lowan, Wisconsin and later phases. 

 It will, however, enlarge our conceptions 

 of the magnitude of the ice age in geo- 

 logical history ; for we cannot deny that 

 the remotest centers of dispersion have 

 been active from the beginning of refrigera- 

 tion. The latest geological epochs are 



fundamentally glacial for the countries 

 above forty degi-ees of latitude on both 

 sides of the equator ; ice-action character- 

 izes the time. The writer has hitherto 

 been esteemed an advocate of unity; but" 

 he has repeatedly insisted that the several 

 margins of glacial accumulation indicate 

 just so many phases of more intense glacia- 

 tion, and that they are to be our criteria 

 of classification. He is satisfied that they 

 can be interpreted to correspond with the 

 several glacial and interglacial epochs es- 

 tablished by Professor Geikie. 



It remains only to notice the chapter upon 

 the cause of the climatic and geographical 

 changes of the glacial period. The ratio of 

 precipitation was the same as now prevails. 

 Snow fields gathered most abundantly in 

 those regions which in our day enjoj^ the 

 largest rainfall. What are now dry regions 

 were formerly regions of limited snowfall. 

 But the amount of precipitation was greater, 

 snow in the north and rain in the south. 

 Arctic currents prevailed near the equa- 

 torial in the cold epochs, but the reverse 

 was true in the interglacial phases. The 

 land seems to have been elevated at the 

 commencement of every cold epoch an<J 

 depressed at its close, submergence having 

 been more characteristic of the glacial than 

 of the interglacial phase. The fiord val- 

 leys were mostly excavated before glacial 

 times. The Scandinavian flora migrated to 

 Greenland after the close of the fourth 

 glacial epoch, when the land was continuous 

 between the continents. There are con- 

 siderations favorable to the Adew that the 

 accumulations of ice in the several glacial 

 epochs produced depressions, not excluding 

 epeirogenic warpings of the crust. The 

 cause of the remarkable connection between 

 glaciation and depression is still an un- 

 solved problem. All the proposed astro- 

 nomical causes of refrigeration are rejected 

 as untenable, except that of Dr CroU, 

 supplemented by Ball, who believed the 



