March 8, 1906] 



NA TURE 



45i 



tions of the Survey, it is physically not an easy book to 

 handle. 



In the first chapter a general discussion leads to the 

 conclusion that the most important factor in metamorphism 

 is the depth of the rocks below the surface. In the upper 

 zone of the earth's crust the chemical changes are such 

 as result in the production of simpler compounds from 

 more complex ones, while in the deeper part the reverse is 

 the case. The starting point of the author's treatment is 

 this antithesis between the upper zone of catamorphism 

 and the lower zone of anamorphism. It appears to us 

 that, while the broad rule here laid down is doubtless of 

 significance, it has scarcely sufficient precision to serve as 

 a basis of classification. The productions of muscovite from 

 orthoclase, and of natrolite from albite, are, according to 

 this geological distinction, catamorphic changes, but it 

 cannot be said that they result in the formation of simpler 

 from more complex compounds. 



The second chapter deals with the forces of meta 

 morphism, and the third with the agents of metamorphism, 

 i.e. especially gaseous and aqueous solutions. This involves 

 a resum& of the principles of physical chemistry, so far as 



Fig. 1 — Fairview Dome, Sierra Nevada, from the north; illustrating tht 

 scales parallel to the periphery as a result of expansion and contrj 



they are applicable to the subject. Although somewhat 

 handicapped bv the author's scepticism concerning the 

 doctrine of electrolytic dissociation, this summary will be 

 very useful to students of geology. Chapter iv. treats of 

 the characteristics of the two zones of metamorphism. 

 The law is found to be that in the zone of catamorphism 

 the alterations are attended by liberation of heat and ex- 

 pansion of volume ; in the zone of anamorphism by absorp- 

 tion of heat and diminution of volume. The zone of cata- 

 morphism is divided into the belt of weathering, lying above 

 the level of underground water, and the belt of cementation, 

 lying below that level ; and the geological processes 

 characteristic of these two belts are contrasted. 



Chapter v., which might perhaps have been abridged 

 without impairing the value of the book, considers the 

 actual alterations undergone in nature by each of the rock- 

 forming minerals. The chemical reactions are illustrated 

 by equations, and the percentage increase or decrease of 

 volume is calculated in each case. The precise application 

 of these calculations is perhaps debatable, since special 

 assumptions have to be made regarding such gaseous and 

 soluble substances as take part in the reactions, and in 

 some cases the equations themselves are rather conjectural. 

 The next three chapters are an analysis of the processes of 



NO. 1897, VOL. 73] 



change in the belt of weathering, the belt of cementation, 

 and the zone of anamorphism respectively. Under the last 

 head the most important discussion is that relative to 

 secondary gneissic and schistose structures. The author con- 

 cludes that " Rock-flow is mainly accomplished through con- 

 tinuous solution and deposition, that is, by re-crystallisation 

 of the rocks through the agency of the contained water. 

 But rock-flow is partly accomplished by direct mechanical 

 strains." The ninth chapter deals with the phenomena 

 of metamorphism of individual rocks, and with this the 

 systematic treatment of the subject ends ; but there remain 

 some interesting chapters applying the principles enunciated 

 in this treatment to certain other branches of geology. 



Chapter x. discusses the difficulties which metamorphism 

 often introduces into stratigraphical investigation and the 

 manner in which these difficulties may be overcome. The 

 next chapter, which is the most novel part of the book, 

 has for its subject the relations of metamorphism to the 

 distribution of the chemical elements. It is shown that, as 

 compared with the parent igneous rock-masses, most sedi- 

 mentary rocks become impoverished in certain elements, 

 which are thus segregated in particular deposits. Some 

 of the numerical results are of a sur- 

 prising kind. Thus, it is calculated 

 that to oxidise the ferrous iron of the 

 original rocks to the ferric state, in 

 which most of it occurs in the sedi- 

 ments, required 35 per cent, of the 

 oxygen now in the atmosphere. To 

 oxidise the sulphur and iron of iron- 

 sulphides to produce the sulphates of 

 the ocean and gypsum deposits, with 

 concurrent transformation of the iron 

 to the ferric form, required one and a 

 half times the oxygen now in the 

 atmosphere. The final chapter, occu- 

 pying no less than 240 pages, might 

 perhaps have been deemed sufficiently 

 complete in itself for separate publi- 

 cation. It is practically a treatise on 

 the principles of ore-deposition. The 

 subject is one upon which much diver- 

 gence of opinion is still found. Prof, 

 van Hise, as is well known from his 

 former writings, has devoted long 

 study to it, and the complete exposi- 

 tion which he now offers will be read 

 with general interest. From his point 

 of view, the majority of ore-deposits 

 have been produced by metamorphism, 

 in the broad sense of the term already 

 defined, and it results that the theory 

 of their genesis consists mainly in 

 bringing the phenomena which they 

 exhibit under the general principles 

 of metamorphism. The conclusion is 

 reached that in many cases the ores 

 have resulted from repeated segregations of the kind con- 

 sidered in the preceding chapter. 



It is impossible to study Prof, van Hise's work without 

 admiring the boldness of his design and the skill with 

 which it is carried out, and being grateful for the stores 

 of carefully arranged information which he has brought 

 together. We must readily admit, too, that he has done 

 good service in insisting upon the necessity for the geologist 

 to familiarise himself with the recent progress of physical 

 chemistry, a knowledge of which, as van 't Hoff and others 

 have shown, is a pre-requisite for attacking many of the 

 most pressing problems of geology. Granting this, how- 

 ever, we may still be permitted to doubt whether a purely 

 geological subject like metamorphism is most advantage- 

 ously dealt with in the manner which is appropriate to 

 the exact sciences. In such a formal schematic treatment 

 there is some danger of making it appear that our know- 

 ledge of metamorphism is to be deduced from chemical 

 principles instead of depending upon observation. Although 

 the criticism would not be a just one in the present case, 

 we venture to express a wish that the author had chosen 

 to describe the facts first and explain them afterwards, and 

 that he had made freer reference to actual rocks and 

 specified localities. A. H. 



lanner in which granit* 

 changes of temperature 



