PETROLOGICAL ABSTRACTS AND REVIEWS 287 



of the discussion. The treatment of the eleolite-porphyries has been 

 rewritten and a section describing the monzonite and shonkinite- 

 porphyries has been added. The fine-grained rocks are divided as 

 formerly into aplitic and lamprophyric series, the former subdivided 

 on the basis of habit, the latter on the geological association and ferro- 

 magnesian constituents. Much of this description has been rewritten. 

 The additional section on the camptonitic, monchiquitic, and alnoitic 

 rocks emphasizes their genetic and geological association with the deep- 

 seated rocks of the alkali series and this relationship is accentuated 

 by the introduction of a number of analyses and an Osann diagram. 



The discussion of the effusive rocks has largely been rewritten with 

 a marked increase in the chemical descriptions which are supplemented 

 by the introduction of many new analyses. The chief changes of view- 

 point occur in the expansion and elaborated classification of the alkali 

 rocks and in the addition of a lamprophyric group of effusive rocks 

 analogous to those distinguished among the dike rocks. The kerato- 

 phyres are now classed with the porphyries of the lime-alkali series 

 because of their geological association, although it is recognized that 

 by mineralogical and chemical composition they are often practically 

 identical with rocks of the alkali series. 



The section on the trachyandesites is entirely rewritten and the line 

 of separation between them and the normal dacites and andesites is 

 emphasized by the introduction of numerous analyses and an Osann 

 diagram. The treatment of the basalts and melaphyres remains with 

 little modification, the author still holding to the distinction of the 3 

 types on the basis of age, although the citation of examples, e.g., the 

 Mesozoic diabases of the United States, is manifestly contrary to the basis 

 of classification adopted. The correlation of the trachydolerites as the 

 effusive form of the essexite-magma is no longer maintained, the view 

 being expressed that their systematic position must be postponed pending 

 the accumulation of additional information. 



The lamprophyric effusive rocks are characterized by their low con- 

 tent of alumina and the almost constant predominance of magnesia 

 over lime. The erection of this new division is based upon the concep- 

 tion that the surface equivalents of the more acid rocks are really more 

 aplitic in their composition and that one would naturally expect to find 

 analogous lamprophyric equivalents as well. To this division are 

 assigned the verite, fortunite, and jumillites of Osann, the orendite- 

 madupite group (and Prowersite) of Cross, the euktolite, coppaelite, 

 absarokite, selagite, and sanukite. 



Part II, devoted to the "Sedimentary Rocks," remains practically 



