332 Reviews — G. P. Iddings — Problem of Volcanism. 



spectrum, greatly preponderate, though variously shaped gaseous 

 varieties are also found. Had Laplace heen in possession of these 

 facts, he, too, would probably have claimed a spiral ancestry for the 

 solar system, and developed his mathematical treatment accordingly. 

 It is not a little curious that Buffon should more nearly have 

 anticipated Chamberlin's hypothesis, which latter, writes Iddings, 

 "will be recognized as a refined expression of the conception of 

 Buffon. The fundamental ideas are alike, the modern expression has 

 had the advantage of a hundred and fifty years of astronomical 

 discoveries and of improvements in the physical sciences." One of 

 the features of the presentation of the hypothesis to-day is the claim 

 that a spiral nebula can easily be conceived capable of meeting the 

 dynamical requirements of a developing solar system in such matters 

 as angular momentum, whereas a discoid gaseous nebula would find 

 itself insolvent if faced with such liabilities. 



According to Chamberlin the central mass of a spiral nebula 

 represents a sun, and the cloudy knots distributed along the coiling 

 arms are the nuclei of planets yet to be, while the nebulous material 

 is the manna upon which these nuclei are to feed until they become 

 perfected. Here, then, is the answer to the original question. The 

 earth may have inherited a large hot nucleus, or on the other hand it 

 may have grown from small beginnings by slow accretion in the cold. 

 Iddings is of the opinion that the latter is the more likely alternative, 

 and is insistent that we have no warrant to assume higher 

 temperatures for the interior of the earth than those that are 

 manifested at the surface through volcanic action, namely from 

 1,000° to 1,500° C. He supports this contention by pointing to the 

 tidal rigidity of the earth, which he thinks suggestive of a restricted 

 internal temperature. The heat of volcanic activity he attributes to 

 condensation, radio-activity, and chemical re-arrangement ; how much 

 relatively should be assigned to each of these three factors he leaves 

 to the future to decide. Joly's name is, of course, mentioned in 

 connexion with radio-activity, but it is strange to read the partial 

 truth that this investigator " considered it probable that radium exists 

 throughout the earth " ; it is not added that Joly is in essential 

 agreement with Strutt in assuming a marked concentration in the more 

 superficial portions. Further, is it a sufficient argument to say that 

 " volcanic rocks do not contain any greater amount of radio-aetive 

 matter than other rocks investigated, so that there cannot be any 

 question of the possible local heating of igneous magmas by this 

 means, as has been suggested by some geologists?" Surely in 

 a uniformly radio-active crust, or even in one in which radio-activity 

 fell off gradually downwards, one would confidently expect increasing 

 temperature with increasing depth because of the relative thermal 

 isolation at low levels. It is a simple conception that at a certain 

 depth fusion supervenes, and that vulcanism is a complex convection 

 phenomenon set in motion by radio-activity. But perhaps Iddings has 

 safeguarded himself in this direction by the use of the word local. 



Like Chamberlin, the author is a convinced adherent of the 

 permanency of ocean-basins, and also of the principle of isostacy in 

 its major applications. He takes an independent line in accounting 



