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THE POPULAR SCIENCE MONTHLY. 



side of the Rocky Mountains in Alberta. 

 The stratified beds, some of them fossilifer- 

 ous, and others containing layers of lignite, 

 which are found in Canada between deposits 

 of till, may probably be explained by moder- 

 ate advances of the ice-sheet interrupting its 

 general recession, not so prolonged nor im- 

 portant as to be called interglacial epochs. 



Prof. T. C. Chamberlin reviewed the his- 

 tory of the Ice age in the United States, 

 concluding that it has probably a threefold 

 division. Two long glacial epochs had pre- 

 ceded the chief time of deposition of the 

 loess, which was followed by the principal 

 interglacial epoch with retreat of the ice bor- 

 der perhaps generally to the northern line of 

 the United States. The last great ice ad- 

 vance and stages of its retreat were attended 

 by the formation of the remarkable marginal 

 moraines, ten to twenty in order from south 

 to north, which have been mapped across 

 the northern United States and portions of 

 Canada, while others doubtless remain to be 

 traced in regions farther north. 



Mr. Warren Upham noted the uniqueness 

 of the climatic conditions of the Ice age, and 

 the absence of glacial periods from the far 

 longer Tertiary and Mesozoic eras. So ex- 

 ceptional climate during the Quaternary era 

 must have resulted from very unusual causes, 

 which could not be astronomic, for in that 

 case records of frequently recurring general 

 glaciation would be found in the long pre- 

 ceding eras. Great uplifts of glaciated coun- 

 tries to such altitude that they received 

 snowfall instead of rain during all the year 

 are regarded as the cause of the ice accumu- 

 lation ; but the vast weight of the ice-sheets 

 finally depressed the land, bringing on a 

 warm climate by which the ice was at last 

 rapidly melted away. Only one epoch of 

 glaciation, with fluctuating advance and re- 

 cession of the ice, is held to be a sufficient 

 explanation for the observed glacial phenom- 

 ena of both North America and Europe; 

 and the Glacial period in each of these con- 

 tinents appears to have ended only some six 

 thousand to ten thousand years ago. 



Mr. Frank Leverett described the diverse 

 deposits of the older drift in northwestern 

 Illinois, showing on a map of that State the 

 courses of the glacial boundary and retreatal 

 moraines which he has traced. Comparison 

 of the depths of stream erosion in the older 



and newer drift indicates that their times of 

 formation were divided by a much longer 

 interval than the time from the end of the 

 Ice age until now. 



In the discussion following these papers, 

 Prof. G. F. Wright spoke of the rock gorges 

 eroded by the Delaware, Susquehanna, and 

 upper Ohio Rivers below the highest drift- 

 gravel terraces. This erosion has been re- 

 ferred to an interglacial epoch, but he finds 

 evidence that it was preglacial, and that the 

 valleys were filled with the early drift gravels 

 from their present bottoms to the level of 

 the high terraces. The general parallelism 

 of the drift boundary' and the successive re- 

 treatal moraines is thought to imply the for- 

 mation of all the drift during a single epoch. 



Prof. R. D. Salisbury cited the much 

 deeper oxidation and leaching of the older 

 than of the newer drift as proof of their 

 widely different ages, separated by a long 

 interval of ice departure and mild climate. 



Major C. E. Button objected to the ex- 

 tension of theories beyond the warrant of 

 facts observed. He thought it too early at 

 the present stage of investigations to decide 

 the causes of the Ice age ; but he doubts the 

 astronomic theory, and looks rather to geo- 

 graphic conditions. 



Lack of time prevented the consideration 

 of the subject assigned for special discussion, 

 on the correlation of glacial formations in 

 opposite hemispheres, which, however, had 

 been more or less touched upon by several 

 of the papers. The prevailing view seemed 

 to be that the glaciations- of Europe and 

 America were nearly or quite at the same 

 time, and that there was a close agreement 

 in the sequence of events constituting the 

 Ice age on both continents. 



The World's Fair Model Library. The 



model library of five thousand volumes shown 

 by the American Library Association at the 

 World's Fair is to be sent to the Bureau of 

 Education at Washington for use and exhi- 

 bition. This library marks a noteworthy 

 step in advance in the choosing of books 

 in each department the selection was com- 

 mitted to an authority in his field. In the 

 sections of electricity, photography, general 

 political economy, and American govern- 

 ment, lists were printed, each title being fol- 

 lowed by a note of description and appraisal 



