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NA TURE 



[Feb. 



country where the rocks are moderately folded, and 

 which was insisted on and fully illustrated in a manual 

 of geology published fourteen years ago, and then 

 could hardly have been said to be new. The distinc- 

 tive characters of mountain chains are treated of in the 

 same spirit. Little, if anything, is here added to the 

 masterly summary of these characters which Dana gave 

 us years ago, but much space is taken up with illustrations 

 of truths which every one admits, in the form of long 

 quotations from sundry sources. .'Ml this speaks to much 

 reading and patient industry, and we cannot but admire 

 the conscientious care with which Mr. Reade has striven 

 to inform himself of all that has been said and done on 

 the subject of which he is treating ; but we cannot help 

 asking ourselves whether it was necessary to print at 

 length the contents of his note-books. This accumulation 

 of evidence, where it is not needed, has brought with it an 

 attendant evil : it has swelled the book to an undesirable size. 

 Now in these busy days, and in the interest of readers, 

 if there is one thing against which, more than anything 

 else, a resolute stand ought to be made, it is unnecessary 

 printing. The day is yet far distant when every page of 

 printed matter shall contain something that is new, and 

 nothing that is not new ; but this is the impossible ideal, 

 the asymptotic consummation, which all writers should 

 ever keep prominently in view. 



But we would not press this point, because, even if 

 the author has given us rather an excess of matter that is 

 not new, what he has given is good of its kind ; and it 

 is of more importance to weigh his arguments against 

 the contraction hypothesis, and in favour of the Scrope- 

 Babbage explanation with the additions he suggests to 

 it. Holding as he does that expansion by heat is the 

 main factor in producing the disturbances of the earth's 

 crust, he made experiments to determine the coefficients 

 of expansion of sundry rocks. He arrives at a mean 

 which agrees very nearly with that found by Mr. Adie. 

 Mr. Reade's experiments ranged from temperatures of 60° 

 to 220° F., and he assumes that the coefficient of expan- 

 sion will be the same for the enormously higher tempera- 

 tures with which he has to deal when considering the 

 case of the earth — a risky proceeding, to say the least. 

 But he has fallen into a far more serious mistake : he has 

 assumed that rocks weighted with a thickness of twenty 

 miles of overlying strata will expand to the same extent 

 for a given increase of temperature as rocks under atmo- 

 spheric pressure. The oversight involved in this assump- 

 tion so thoroughly vitiates all his numerical results that 

 no conclusion can be drawn from them. 



In Chapter XI. we have the objections to the contrac- 

 tion hypothesis succinctly stated. The numerical results 

 we put aside for reasons just given, but in his general 

 argument the author does not seem to us to realise the 

 full meaning of the hypothesis. He seems to hold that 

 according to the contractionists crumpling is produced 

 by unequal contraction in the solid shell itself, which 

 certainly is not their view. And he entirely omits all 

 reference to the one fact which is the life and soul of the 

 hypothesis, that the earth's crust is not strong enough to 

 stand by itself without support, a fact which admits of 

 rigid mathematical demonstration. It is a decided case 

 of a seriously mutilated representation of the play of 1 

 " Hamlet." 



We cannot therefore admit that Mr. Reade's arguments 

 are very damaging to the hypothesis against which they 

 are directed ; and we cannot see how expansion due to 

 rise of temperature could alone produce the results which 

 he attributes to it. The strains produced in this way 

 would tend to be relieved by yielding in the direction of 

 least resistance — that is, vertically ; and if there were 

 no impediment to the perfect transmission of strain, the 

 yielding would be wholly in this direction. In the actual 

 case a certain amount of deformation would doubtless 

 be produced within the heated mass itself, but hardly 

 enough, it would seem, to cant over a huge anticlinal, 

 and lay it nearly flat on its side. The machinery invoked 

 by the contraction hypothesis may or may not have been 

 the means by which such overthiusts were brought about, 

 but it is the only machinery yet suggested which seems 

 competent to produce them. " Seems," we say through- 

 out, for the question between rival hypotheses is as yet 

 only one of probability. 



And we think no one will contend that the Scrope- 

 Babbage hypothesis ought to be entirely put on one side 

 when we speculate on the cause of earth-movements ; 

 great broad folds, such as those of the plateau-region of 

 Utah, described by Capt. Dutton, and figured on Plate 

 39 of the book, may have been caused by the bulging up 

 of heated masses below, though they can be explained 

 equally well by the contraction hypothesis. 



It remains to notice that the book is rich in figured 

 illustrations. A number of the plates are devoted to 

 somewhat diagrammatic landscapes of contorted rocks, 

 and these bring out well the points they are intended to 

 illustrate ; but they do not add to the stock of our know- 

 ledge. They would be serviceable to a geologist, if such a 

 one there be, who had never stirred out of the fen-country, 

 but he of course would do still better if he took an excur- 

 sion ticket to some of the localities from which the views 

 are taken. A. H. Green 



ORGANIC EVOLUTION 

 The Factors of Organic Evolution. By Herbert Spencer. 

 (London and Edinburgh : Williams and Norgate, 

 1887.) 



MR. HERBERT SPENCER has done well to reprint 

 in a permanent form his two articles on the 

 " Factors of Organic Evolution," which were published 

 last year in the Nineteenth Century j for, although they 

 present substantially the same doctrines as are to be met 

 with upon this subject in his " Principles of Biology," they 

 do so in the light of fuller knowledge and more matured 

 judgment. 



The object of the essay is that of taking stock, so to 

 speak, of natural selection as compared with other 

 '' Factors." Mr. Spencer's treatment of this subject is 

 admirable, and ought to be read by all working naturalists 

 who have any interest in the problems of evolution. The 

 literature of Darwinism has now become so extensive that 

 even first-rate naturalists who are engaged on other lines 

 of work are apt to get left behind, or, with respect to 

 Darwinism, themselves to become examples of what are 

 now called " vestiges " : their ideas are the superseded 

 survivals of some previous phase of evolutionary science. 

 And most of all is this true with regard to the funda- 



