August i6, 1889.] 



SCIENCE. 



119. 



concluded that there is no general appreciation of its great signifi- 

 cance. One may hardly find a history of the United States that 

 does not give an introductory account of the early Indians ; and 

 yet it is safe to say that they are of less importance in forming an 

 understanding of our historic progress than the work of the old 

 glaciers is in gaining a conception of our geography. The mo- 

 raines and drumlins, the kames and sand-plains, the lakes, falls, and 

 gorges, the gravel-filled and terraced valleys that characterize the 

 northern glaciated country, are, to be sure, relatively small topo- 

 graphic forms ; but they are forms on which we live, and which 

 we daily see around us. It is proper that they should be intro- 

 duced to public notice ; and Professor Wright's book will certainly 

 aid in calling attention to them, particularly if his readers go fur- 

 ther than his text, and follow up his footnotes, through which they 

 will be led to the most important discussions on these subjects. 

 Look, for example, at the illustration of a new river-course marked 

 by a waterfall, or of an old river-course blockaded into a lake, both 

 of these excellent views being copied from Chamberlin and Salis- 

 bury's invaluable essay on the driftless area of Wisconsin ; or at 

 the strongly marked morainic wall of the Kettle range in Wiscon- 

 sin, taken from one of Chamberlin 's reports; or at the extraordi- 

 nary loops of the moraines in Minnesota and Dakota, taken from 

 Upham's and Todd's figures ; or at the drumlins reproduced from 

 Hitchcock's report on New Hampshire; or at the^map of the 

 kames of Maine by Stone. All of these are not only valuable il- 

 lustrations of highly significant topographic forms, they are also 

 tempting suggestions towards study of the original sources on 

 which Professor Wright has drawn freely in preparing his book. 

 The same may be said of numerous quotations, often extended 

 over a page or more, from the writings of those who have given us 

 the best interpretations of glacial geology. There are extracts 

 from Gilbert's and Pohlmann's papers on the recession of Niagara 

 Falls ; Winchell's account of the post-glacial recession of the Falls 

 of St. Anthony ; Upham's description of Lake Agassiz, now the 

 great wheat-growing plain of Minnesota and Dakota ; Claypole's 

 suggestive although rather highly deductive account of the tem- 

 porary lakes marginal to the retreating ice-sheet ; Newberry's 

 studies on pre-glacial drainage ; and many more. The thoughtful 

 reader of all this will perceive something of the long growth of the 

 present belief in glacial geology, and of the efforts of the many 

 workers who have so greatly contributed to its understanding. 

 Professor Wright's own observations on the margin of the glaciated 

 tract are of course also described. 



Among the questions on which the conclusions favored by the 

 author are most likely to find dissent with some investigators are 

 the date and duration of the glacial period, and the ice-dam at 

 Cincinnati, by which the Ohio was blocked into a great lake. The 

 objections to the latter theory are not so much on account of its 

 inherent improbability as because the effects and products of such 

 a lake have not been as yet clearly eriough seen to require a mod- 

 erate sceptic to admit its existence. It is natural enough for Pro- 

 fessor Wright to feel a paternal fondness for this idea, which he 

 originated some years ago, and look with favor on facts that point 

 towards it ; but, before it can command general acceptance, it 

 must be examined in the light of a broader view of the evolution of 

 rivers and of the various changes to which they are subject. It 

 does not seem as if this broader view has been attained, for it is 

 said that the Ohio has been at work on its present valley from the 

 first elevation of the continent to glacial time, that is, through all 

 mesozoic and nearly all cenozoic time; whjle it must be apparent 

 to the student of river history that the present valley of the Ohio is 

 of by no means so great an age. The water-worn pebbles on high 

 land in West Virginia have relatives in similar deposits in Ten- 

 nessee, outside of the hypothetical Ohio lake. The terraces of 

 western Pennsylvania are not described in such a way as to make 

 it clear that they are of lacustrine and not of fluviatile origin. The 

 case had best stand open yet for a time till fuither facts are de- 

 veloped. 



The date of the glacial period commonly alluded to, as deter- 

 mined by such post-glacial river-gorges as the Niagara, is rather 

 the date of a somewhat late phase in the disappearance of the ice. 

 How long a time elapsed from the maximum advance of the ice to 

 the beginning of work on the gorge is not now determinate. The 



unknown factors in this problem are very numerous, and they will 

 require much labor in their definition. Prominent among these is 

 the time-interval between the various terminal moraines and drift 

 margins ; and in this question, Wright differs from the conclusions 

 of Chamberlin, McGee, and Gilbert, as to the division of the glacial 

 period into two distinctly separate epochs, and regards the whole 

 period as essentially single and continuous. Extracts are given 

 from the writings of the above-named investigators ; but the reader 

 will do well to consult the original essays, as the discussion is 

 rather intricate. Here, as in the case of the ice-blocked Ohio, it 

 appears to me that Professor Wright does not sufficiently consider 

 other arguments than those of strictly glacial geology. The evi- 

 dence of topographic development, as adduced by Chamberlin and 

 McGee, particularly needs further examination. 



On these larger questions, it is to be hoped that an open mind 

 can be maintained for some years to come. It is only by regard- 

 ing them as settled that the student may be unwisely guided. The 

 treatment of the smaller subjects, such as those of which many 

 examples have been named above, will prove instructive to many 

 readers. W. M. D. 



An Elementary Treatise on Mechanics. Part I. Statics. By 

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This is a compact and well-arranged little volume, intended for 

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Steam Engine Design. By Jay M. Whitham. New York, 

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Mechanical engineers, students of engineering, and draughts- 

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The more general elements pertaining to steam-engine practice, 

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