338 Washington — CharnocJcite Series of Igneous Hocks. 



equal to the combined alkalies and lime, and with wide varia- 

 tion in the silicity. 



In some respects the rocks of the regions described resemble 

 those of the Ural mountains, but these last carry augite gen- 

 erally instead of hypersthene, olivine and magnetite rocks are 

 common ; and chemically they are higher in lime and with 

 magnesia much higher than iron oxides. The range in silica 

 is also much less, the silicity being lower and seldom or never 

 attaining that of the intermediate members of the other series. 

 The resemblance in some respects to and difference from the 

 eastern Canada and Adirondack regions have already been 

 touched on. 



It is obvious that the five regions here discussed differ 

 markedly in their essential characters from the usual regions 

 belonging to the so-called subalkalic, calci-alkalic or Pacific 

 tribe. Indeed, so marked is this distinction that Wolff* 

 reckons them with the rocks of his " Arctic tribe," constituted 

 essentially of basalts and basaltic rocks. The peculiar charac- 

 ters brought out in this paper, however, distinguish them 

 clearly from the ordinary basaltic or gabbroic rocks, and such 

 a conjunction is, to my mind, unjustified. 



This is not the place for a discussion of the much-mooted 

 question of the Atlantic and Pacific branches. Dalyf shows 

 the irrelation of the type of crustal movement to the magmatic 

 character, and I have briefly pointed out;}; the irrationality of 

 referring the many varied and complex types of magma and 

 comagmatic regions to only two contrasted branches. The 

 well-established occurrence in widely diverse parts of the earth 

 of such a group of comagmatic regions as those represented by 

 the charnockite series, with their common very distinctive 

 peculiarities, mineralogical and chemical, which are markedly 

 different from the usual " sub-alkalic" or " Pacific" rocks, con- 

 stitutes another instance which illustrates the untenability of 

 the doctrine of Harker, Becke and their followers. 



Geophysical Laboratory, 



Carnegie Institution of Washington, 

 Washington, D. C, Dec. 12, 1915. 



* F. v. Wolff, Vulkanismus, i, p. 153. 1914. 



fR. A. Daly, Igneous Rocks, p. 412, 1914. 



JH. S. Washington, C. R., xii, Congr. Geol. Int., p. 237, 1914. 



