REVIEWS 169 



years is ample to account for geologic phenomena. Prof. Sollas was satisfied with 

 26 millions of years, and, though his recent work shows some sign of a modifica- 

 tion of that opinion, the discrepancy between the results is great and glaring. 



On this side, Mr. Holmes's work must be described as weak. He neither 

 proves his case nor, in attempting to do so, does he make the best use of the 

 materials at his disposal. A considerable portion of the book may be dismissed 

 as padding. Pictures and descriptions of spiral nebulas, and of the polar caps of 

 Mars, look very pretty in a semi-popular work, but they have the remotest bearing 

 on the matter in hand. Mr. Holmes is an advocate of Prof. Chamberlin's 

 planetesmoid hypothesis. He thinks that, after the first sediments were formed 

 (p. 31), the Earth was still growing by reason of the capture of planetesmals. The 

 speculation seems exceedingly improbable, and, indeed, we are entitled to ask 

 why we find no traces of the occurrence in the earliest sedimentaries, but this and 

 others matters we may pass by as side issues and irrelevant. 



To come to the sections that really matter, the problem of the duration of solar 

 heat presents the greatest difficulty. Mr. Holmes could not be expected to make 

 much of this. At the time his book was written, no adequate theory of the subject 

 was published, though there have been vague anticipations in articles by the 

 Messrs. Jessup 1 and others. Mr. Holmes accepts Prof. Arrhenius's idea of the 

 existence in the Sun of compounds which contain vast stores of energy due to 

 exceptional conditions of great heat and pressure (p. 119). There is no space to 

 criticise this view. It will be sufficient to point out that it is entirely inconsistent 

 with the planetesmal hypothesis, because the planetesmals, ex hypothesi, are not 

 subject to great heat and pressure. Chamberlin's planetesmals and Arrhenius's 

 internal heat certainly form a curious eclectic mixture. 



The other points that call for attention are Prof. Joly's researches on the 

 saltness of the sea, and Prof. Sollas's on the thickness of the sedimentary rocks. 

 With regard to neither of these does Mr. Holmes appear to be aware of recent 

 literature. As a chemist, Mr. Holmes ought to know something of the special 

 liability to error of the average sodium analysis of river water, especially when (as 

 is usually the case) no particular trouble is taken to assess it with the necessary 

 accuracy. There is a continual tendency towards unduly high results. The fact 

 has been pointed out repeatedly by Mr. Acroyd, Prof. Dubois, and myself. 2 Nor 

 does Mr. Holmes appear to realise the cumulative effect of the errors. Mr. 

 Holmes's conclusion that the quantitative deductions are purely provisional is 

 correct, but his reasons are very inadequate. 



Nor, in his discussion of Prof. Sollas's theories of sedimentation, is he much 



happier. Prof. Sollas is a geologist of the highest rank, and certainly deserves 



the compliment of detailed refutation. On this matter, Mr. Holmes's view, which 



he supports by a private communication from Prof. Chamberlin, is that land 



radients to-day are much higher than the average, and that, consequently, the 



1 Philosophical Magazine, January 1908. 



3 Particularly in the following papers : 1. Proceedings Geological Society 

 Yorkshire, 1902 (on Cyclic Salt); 2. Chemical News, 1901 (Discussion between 

 Mr. Acroyd and Prof. Joly) ; 3. Proceedings Amsterdam Academy, 1902 (On the 

 Ratio between the Sodium and the Chlorine in the Salts carried by the Rivers 

 into the Sea) ; 4. Chemical News, May 30, 1909 (On the Sodium and the Chlorine 

 in River and Rain Waters) ; 5. Journal of Geology, 1910 (The Age of the Earth 

 and the Saltness of the Sea) ; 6. Contemporary Review, February 191 1 (Modern 

 Theories of Geologic Time). The latter paper also contains a criticism of Prof. 

 Sollas. 



