I 1t7) REGINALD A. DALY 
aplites are explained, vogesites, spessartites, and odinites are not. 
If tinguaites or nephelite pegmatites represent residual liquids, 
what is the meaning of the camptonites or alndites, so closely asso- 
ciated both in time and space with those alkaline types? In some 
nephelite-syenite areas camptonites not only are abundant but 
appear to be even younger than most of the tinguaites. There is 
manifest trouble in explaining both the salic and femic dike groups 
as crystallizations from residual liquid.* 
Considering the weakness of the idea relating alkaline magmas 
to crustal dislocation of a special kind, Smyth’s conception needs 
an important supplement. It would be strengthened if a more 
probable cause for the local, quite exceptional, concentration of the 
mineralizers and alkalies in purely juvenile magma were discovered. 
This has not yet been done. On the other hand, the local assimila- 
tion of sediments cannot, in general, fail to enrich subalkaline 
magmas in gaseous constituents, with the effect of segregating the 
alkalies, as the writer has long held.?_ In short, the combination of 
juvenile and resurgent “mineralizers” is believed to be a much 
« A. Harker (oP. cit., p. 558) recently published a very doubtful argument in support 
of his contention that subalkaline (‘‘calcic”’) rocks rather than alkaline rocks are 
genetically associated with ‘‘regions subjected to powerful lateral thrust.’ He writes: 
“Tf we examine those crystalline schists which are admittedly of igneous origin, 
together with foliated igneous gneisses, we find that they belong almost exclusively 
to the calcic branch. .... Alkaline crystalline schists as a whole are quite insig- 
nificant as compared with any single type in the calcic division. ... . The striking 
disparity here noted is only one consideration among others which points to a peculiar 
distribution of alkaline and calcic igneous rocks in rélation to crustal stresses.” 
Evidently the dynamic metamorphism in most of the cases cited followed after 
the respective eruptions. Some of the intervals between eruption and shearing have 
been proved to equal several geological periods. Can one assume that the resulting 
schistosity of the igneous bodies has any connection whatever with the generation of 
their magmas? Moreover, there is much to be said for the view that the schistosity 
and foliation of pre-Cambrian rocks largely originated during static metamorphism 
rather than during the operation of lateral thrust. It may be observed that neither 
great volumes nor wide distribution for the alkali-rich rocks would be expected in the 
older pre-Cambrian terranes by an upholder of the sediment-syntectic explanation of 
alkaline rocks. 
2 From the composition of the amygdale minerals in the alkaline lavas of Mozam- 
bique, A. Holmes (Nature, XCVIII [1916], 162) believes the corresponding magmas 
to have been rich in carbon dioxide as well as undersaturated in silica. The same 
author describes calcite inclusions in the analcite and nephelite of nephelinite at the 
Lucalla River, Angola, West Africa (Miner. Mag., XVIII [1916], 64). 
