212 REVIEWS 



discussion of the rocks. Certain included masses in the granite, 

 apparently resembling those common in orbicular granites, are shown 

 to be fine-grained hornblende-mica-syenite, and it is suggested that 

 their origin may be due to liquation. It is pointed out that the 

 occasional reference of micropegmatitic structure to secondary changes 

 as suggested by Irving, Hobbs, and Romberg, rests upon slight evi- 

 dence and involves rather violent assumptions as to the method of 

 corrosion. 



Aplitic dikes carrying floated fragments of biotite and feldspar 

 similar to the inclusions in the minette dikes at Aschaffenberg were 

 noted. Ilmenite was found altering to leucoxene, which proved to be 

 anatase rather than titanite. A quartz-tourmaline-porphyry is described. 

 The rock occurs as an intruded sheet having a felsitic groundmass, 

 quartz phenocrysts, feldspar flecks, and radial and stellate groups of 

 fibrous tourmaline. It carries fluorite, and is referred to pneumatolitic 

 processes. Among the lamprophyres are augite-vogesites, minettes 

 and raonchiquites. The latter are of interest as occurring here in con- 

 nection with a granitic mass rather than with eleolite-syenite. In 

 connection with this description of the monchiquites is given a note 

 by Kemp correcting an analysis of a similar rock published by him in 

 Bull. U. S. G. S. 107. The basalt carries occasional quartz, but offers 

 no new evidence as to its primary or secondary origin. It is pointed 

 out that the term divitrification, as used in petrography, does not 

 necessarily mean strictly secondary action, since certain spherulites are 

 produced in the process of cooling and while the rock is still viscous. 

 Johnston-Lavis' theory that the variation in rocks is produced by the 

 solvent action of the magma upon the conduit is shown to be unten- 

 able so far as this area at least is concerned. The molecular ratio 

 between the alkalies of the most basic and most acid rocks of the series 

 is 125 : 50. This would then require for the production of the latter 

 the solution of at least an equal bulk of rock wholly free from alkali. 

 Furthermore, the acid rocks which, according to the theory, should be 

 first erupted was not first but relatively late. Finally, the dioritic mass, 

 erupted through very basic shales, becomes more acid rather than more 

 basic towards the periphery. 



The report is well illustrated, and is of interest, not only from the 

 fact that it deals with a hitherto practically unknown area, but because 

 of the light shed by it upon these more general problems. 



H. F. Bain. 



