Apml 20, 1917] 



SCIENCE 



387 



Van Hise, are designated as katamorphic and 

 anamorpliic. 



The object of the book is said by the au- 

 thors to be the presentation of the current 

 knowledge of this comprehensive subject in 

 some perspective by means of quantitative 

 methods of comparison and discussion. They 

 say " It is not a handbook of metamorphism in 

 which one may expect to find an adequate de- 

 scription of metamorphic details." There is 

 no description of a metamorphic rock any- 

 where in it. It is evidently prepared for stu- 

 dents who have a knowledge of the petrography 

 of all kinds of rocks, and the ability to deter- 

 mine minerals optically and chemically. It is, 

 in fact, a book for advanced workers in petrol- 

 ogy and for geologists interested in the broad 

 problems of sedimentation and the redistribu- 

 tion of mineral matter in various ways. 



The authors are unable to follow Van Hise 

 in the emphasis he placed on his so-called zones 

 of katamorphism and anamorphism, for, as 

 they remark, so many other factors than depth 

 enter into the processes of alteration that at 

 any depth, or at the same depth at different 

 times, the changes may be in opposite direc- 

 tions for different kinds of rocks. Or, as they 

 have also expressed it, " Depth is only one of 

 the factors determining intensity of condi- 

 tions. Igneous intrusion, mineral and chem- 

 ical composition, the differential stress condi- 

 tions, etc., all play their parts." 



In Part I. the decomposition, or katamorph- 

 ism, of rocks is discussed with respect to sev- 

 eral types of rocks as illustrated by specific in- 

 stances, such as a granite from Georgia, and a 

 gabbro or diabase. Another example is the 

 production of bauxite from nephelite-syenite, 

 which is called an " acid igneous rock," and 

 the production of laterites from " basic " ig- 

 neous rocks. The decompositions of ores and 

 of sedimentary rooks are also discussed. In 

 each case the mineral and chemical changes, 

 as well as those of volume and density, are 

 considered in general terms. This is followed 

 by a speculative discussion of the probable re- 

 distribution of the constituents of the average 

 crystalline and igneous rock during decompo- 

 sition. The speculative character of the dis- 



cussion rests upon its apparent quantitative 

 elements, since it is necessary to assume defi- 

 nite quantitative values for factors concerning 

 which there can be no definite quantitative 

 knowledge. Moreover the petrographical basis 

 of the discussion is open to serious question in 

 that it assumes that all igneous rocks may be 

 embraced under the terms " acid " and " basic," 

 or granites and basalts (!), and that estimates 

 of the average composition of these have defi- 

 nite values. The value of deductions derived 

 from general averages of highly complex fac- 

 tors is always doubtful for the reason that an 

 average is too often a graveyard of facts. 



Part II. deals with the construction or inte- 

 grating changes in rocks, or anamorphism. It 

 includes cementation, dynamic metamorphism 

 and contact or thermal metamorphism. Vari- 

 ous types of rocks are considered with refer- 

 ence to these possible modes of transforma- 

 tion; clays, sands, carbonates, igneous rocks, 

 mineral deposits and ores. The cleavage and 

 textures of the crystalline schists are discussed 

 at considerable length, and the discussion 

 closes with a general review of the results of 

 anamorphism and of the probable processes, 

 the conclusions being of special interest and 

 importance, but too extensive to be cited here. 



There follows, in Part III., a general dis- 

 cussion of metamorphism in the broad sense in 

 which the authors use the term, which is made 

 to include a discussion of the origin of resid- 

 ual clays and soils, glacial deposits, trans- 

 ported clays and muds, sands and sandstones, 

 calcareous sediments and crystalline schists. 

 In the case of the schists it is found from an 

 investigation of chemical data that " chemical 

 criteria do not satisfactorily discriminate 

 schists of sedimentary and igneous origin." 

 They fail in those cases where other criteria 

 fail. The discussion also considers ocean, lake, 

 river and underground solutions as by-prod- 

 ucts of the metamorphic cycle, and the authors 

 suggest that the metamorphic cycle be made 

 the basis for the genetic classification of com- 

 mercial mineral products. 



In concluding the discussion they say that 

 " The metamorphic cycle may be regarded as 

 indicative of a great pulsational alteration of 



