REVIEWS 747 



sediments and of the relative proportions of the more important classes of 

 sediments. Combining these assumptions with the results of chemical 

 analyses, the losses and gains of various formations for each of the important 

 elements of the earth are considered. Many surprising results are reached. 

 For instance, we find the conclusion that to oxidize the ferrous iron of the 

 original rocks to the ferric condition in which most of it occurs in the sedi- 

 mentary rocks, 35 per cent, of the amount of oxygen in the atmosphere has 

 been required. But still more starthng is the conclusion that to oxidize the 

 sulphur and iron of iron sulphides in order to produce the sulphates of the 

 ocean and gypsum deposits, and to transform the iron to the ferric form, 

 required one and one-half times the amount now in the atmosphere. 



The final chapter of the book, 12, is upon the relations of metamorphism 

 to ore deposits. It is probable that this chapter will receive more general 

 attention than any other. The material of the other chapters is of a kind 

 which is likely to be of interest to the geologist only, whereas this chapter 

 is of interest to all men concerned in the great mining industry. The 

 chapter on ore deposits occupies 240 pages, and, indeed, might have 

 been named "The Principles of Ore Deposition." From the author's 

 point of view, the majority of ore deposits are produced by metamorphic 

 processes. Having worked out the general principles of metamorphism 

 with reference to rocks, the author found that the application of these 

 principles to ore deposition explained the majority of ore deposits. From his 

 point of view the proper theory of ore deposition consists mainly in bringing 

 the particular phenomena exhibited by ore deposits under the general prin- 

 ciples of metamorphism. The chapter contains a new classification of ore 

 deposits, the fundamental divisions of which are the same as those of rocks. 

 Thus ore deposits are divided into three classes — those of sedimentary 

 origin, those of igneous origin, and those of metamorphic origin. Strictly 

 the treatise on metamorphism should, perhaps, have considered only the 

 third class. However, the first and second classes are sufiiciently discussed, 

 so that the relations of these ores to those produced by metamorphic pro- 

 cesses may be appreciated. The discussion of ore deposits is too elab- 

 orate to be summarized in this general statement. But it may be remarked 

 that for the metamorphic ores an attempt is made to trace out the solution, 

 transportation, and precipitation of each of the chief economic metals. 

 Also the alterations and further segregation of metals are fully considered. 

 The conclusion is reached that in many cases an ore deposit does not 

 represent a single segregation, but is the result of repeated segregations by 

 the same general processes which result in the depletion in certain elements 

 of the various rock formations and their segregation elsewhere. In other 



