GENESIS OF THE ALKALINE ROCKS III 
Action of “‘mineralizers”’ and of normal faulting.—Cross, Bowen, 
Foye, and others approve Smyth’s reference’ of the alkali-rich rocks 
to the work of gases or ‘“‘mineralizers’’ operating in subalkaline 
magmas. ‘The pneumatolytic origin of many nephelitic, sodalitic, 
and cancrinitic rocks has indeed long been clear to the French and 
other intelligent students of their mineralogy and texture. The 
next important questions are as to the origin of the gases and the 
cause of the concentration of the gases. Smyth regards the gases 
as (p. 45) “‘magmatic or ‘juvenile’ rather than resurgent”? and 
joins Harker in thinking that their concentration along with the 
alkalies probably depends on crustal dislocation by radial move- 
ments in the earth. 
He makes no other suggestion as to the reason why the mineral- 
izers Should, in general, not have the power to develop nephelite 
syenites and similarly undersaturated rocks in most plutonic com- 
plexes. Water and other mineralizers form tremendous emanations 
in andesitic volcanoes, yet many of these lack phonolitic, trachytic, 
or other alkali-rich lavas. The present writer has shown that 
many alkaline bodies occur in zones of intense tangential compres- 
sion, while, on the other hand, subalkaline bodies are abundant 
in areas of radial dislocation. The statistics of distribution are far 
from supporting Harker’s thesis. It suffers also from the improb- 
ability of another underlying assumption—that in every instance 
the parent subalkaline magma was nearly frozen at localities where 
normal faulting has caused the eruption of multitudes of small 
alkaline masses. The mechanism is seen to be one of almost 
infinite delicacy and hence of doubtful reality, at least on the scale 
demanded. One may observe also that normal faulting need not 
exert a notable squeezing-out effect if the magma chamber were not 
cut by the fault planes. A semiliquid mass inclosed in a down- 
thrown or upthrown block would not necessarily undergo any 
differential stress. The alternation of liquid basalt and trachyte 
or phonolite at the same volcanic center is one of the more obvious 
difficulties with the speculation. 
Further, the Harker hypothesis does not take proper account 
of the lamprophyres which usually close petrogenic cycles. While 
21@i He Smyth yiops cs py33: 
