114 REGINALD A. DALY 
volatilized from a sedimentary syntectic and then concentrated 
either in the same magma chamber or in satellitic chambers. 
Whether the necessarily complex solutions will carry the alkalies 
free or as carbonates, aluminates, hydrates, silicates, or alumo- 
silicates 1s a problem not now to be solved, but it cannot 
fail to be considered by the serious student of the assimilation 
theory." 
Perhaps, too, experiment may yet tell the essential reason for - 
leucitic (potash-rich) differentiates in one body and nephelitic 
(soda-rich) differentiates in another. Leucite, nephelite, and soda- 
lite accompany such minerals as garnet, melilite, hauynite, and 
plagioclase in industrial slags. It would be of interest to know 
what contrasts of crystallization there may be in artificial melts, 
otherwise similar but with pure calcite as the only carbonate flux 
of the one group of melts and pure dolomite as the only carbonate. 
in the other. Why is albite concentrated in spilite and orthoclase 
in the “orthoclase basalts’ ?? The reply, that each is due to 
differentiation, is hardly a reply at all. One needs to know what 
was the cause of each differentiation and what it was that differ- 
entiated. 
BOWEN’S EXPLANATION OF THE ALKALINE ROCKS 
Summary of his general theory.—Basing his results on an un- 
matched group of experiments, Bowen has given to the world a 
““systematic petrogenic theory”? which is deeply concerned with 
the alkaline rocks. Since the validity of his theory on this side 
depends on the general mechanism assumed, a considerable amount 
of attention must be given to main principles before the special 
reasoning applied by Bowen to the alkaline suite can be properly 
weighed. 
His views may be summarized in his own words (pp. 89, 90): 
“Consideration of the factors limiting its scope has led to the 
decision that assimilation is, relatively speaking, an unimportant 
* Compare G. W. Morey’s thorough study of the ternary system, HA0—K,Si0O;— _ 
SiO., reported in the Jour. Am. Chem. Soc., XX XIX (1917), 1173. 
2S. H. Reynolds, Quart. Jour. Geol. Soc., LXXII (1917), 23. 
3N. L. Bowen, Jour. Geol., Suppl., XXIII, tors. 
