Reviews — Professor W. IT. Hobbs — Existing Glaciers. 569 



low that they drained to the bottom any lakes that may have once 

 existed." The effect of the icy barrier in damming up streams and 

 rivers and forming huge temporary lakes and smaller lakelets is well 

 told in these pages from the observations of numerous geologists, 

 including the author ; while in other instances the torrents of glacial 

 water that were poured into the Mississippi and Ohio were of great 

 magnitude, and there are indications that glacial floods rose in the 

 Lower Missouri to a height of 200 feet or more. 



Dr. Warren Upham contributes an account of " The Glacial Lake 

 Agassiz ", and particulars of Lake Allegheny are printed from an 

 unpublished report of Professor E. H. Williams. 



Of the erosive and transporting power of moving ice much information 

 is given; and the view advocated by Newberry that glacial ice " was 

 a prominent agent in the formation of the Great Lakes " is sym- 

 pathetically treated by the author. 



We have given, mostly in his own words, some account of the 

 principal subjects dealt with in this volume : with these we should 

 also mention the influence of the Glacial Period on the distribution of 

 plants and animals. To the two chapters on "The Cause of the 

 Glacial Period" some "Supplemental Notes " are contributed by 

 Dr. Upham, who deals with the effects of great epeirogenic elevations, 

 and with the views of Messrs. Chamberlin and Salisbury on the 

 meteorological effects of the depletion of atmospheric carbon dioxide 

 by reason of the increased area of land and the increased carbonation 

 and oxidation of rocks. Winds and ocean currents are naturally 

 regarded as important factors in the Glacial Period, and reference 

 might have been made to Mr. F. W. Planner's paper on "The Influence 

 of the Winds upon Climate during the Pleistocene Epoch " (Q.J.G.S., 

 lvii, p. 405, 1901). With regard to the date of the Glacial Period, the 

 author is disposed to support a much lower estimate for the duration 

 of the Ice Age than the 200,000 years he suggested in 1908 (Q.J.G.S., 

 lxiv, p. 149) ; and he considers that the period may have ended about 

 10,000 years ago. Evidence is given of the presence of remains of 

 man in the early stages of the Glacial epoch and possibly in Pliocene 

 deposits. 



II. — Characteristics of Existing Glaciers. By William Herbert 

 Hobbs, Professor of Geology in the University of Michigan. 8vo ; 

 pp. xxiv, 301, with 34 plates and 140 text-illustrations. New 

 York: The Macmillan Co., 1911. Price 13s. 6d. net. 



IN this work the general knowledge of the movements of ice and its 

 influence in shaping many features of the earth's surface is ably 

 expounded and admirably illustrated. 



The work is divided into three parts, dealing with Mountain, Arctic, 

 and Antarctic Glaciers ; and the author dwells particularly on the 

 distinctions, not only in size, but in origin, movements, and influence 

 on the earth's surface, between the large continental glaciers or ice- 

 sheets and the Alpine or mountain glaciers. As he remarks, the 

 continental ice assumes a form the visible surface of which is largely 

 independent of the rocky foundation on which it rests, while mountain 



