REVIEWS 741 



the center of a trianij^le and by increase in soda passes through akerite 

 and lavurikite to nepheline syenite; by increase of potash through 

 jilauenite and potash-feldspar-syenite to a hypothetical leucite syenite ; 

 and fmallv, by increase in lime, through alkali-rich diorite and alkali- 

 poor diorite into an acid lime-rich norite, etc. 



The pyroxenites of the region are basic peripheral facies of the 

 normal monzonite. They were the first to solidify, as detached masses 

 of pyroxenite are frequently included in the monzonite. The latter 

 rock frequently shows porphyritic facies on its periphery, as is com- 

 mon in the Christiania region. 



The monzonites and their peripheral facies are not the only erup- 

 tive rocks of Triassic age in this region. The complete series, and the 

 sequence of eruption, is summed up by Brogger as follows : 



(i) The oldest eruptions of Triassic time are represented by basic 

 dikes and effusive rocks ; melaphyre, augite-porphyrite, amygdaloids, 

 tuffs, etc. 



(2) Corresponding to the later eruptions of these basic dikes and 

 effusive rocks, are also basic plutonic rocks (essentially pyroxenite, 

 passing into gabbro-diabase, monzonite, etc.) of which relatively only 

 insignificant masses are preserved as peripheral facies of more acid 

 rocks. 



(3) These more acid rocks, essentially monzonite, are of interme- 

 diate conjposition and belong to an independent rock-group within 

 the series of the orthoclase-plagioclase rocks. 



(4) Younger than the monzonites and the corresponding effusive 

 rocks, are the red granites of Predazzo ; also, probably, small veins of 

 aplite and dikes of quartz porphyry. 



(5) The youngest eruptions of the whole eruptive epoch are repre- 

 sented by an association of dikes ; these are partly of ultra-basic com- 

 position, essentially camptonites, and partly of intermediate composi- 

 tion, commonly " liebeneritporphyre," or nepheline-bostonite. These 

 two groups are related as complementary dikes. The bostonites 

 appear generally to represent the youngest eruptions of the whole 

 epoch. 



Before applying the facts gained in the Tyrol to the study of the 

 Christiania region, the author discusses the general laws governing the 

 mechanism of eruption of plutonic rocks, and especially the hypothesis 

 due to Kjerulf, Michel -Levy, and Suess, that the granites are batho- 

 lithic, not laccolithic, and have displaced the invaded rocks by fusing and 



