100 REGINALD A. DALY 
syenites was speculatively treated. For those rocks, the most 
voluminous of the whole alkaline suite, ydrous, basic sediments 
(with or without calcareous associates) were considered as the prob- 
able agents of desilication and concentration of alkalies.t Thus, 
while the absorption of small amounts of limestone or dolomite 
seems to be the chief cause for the differentiation of most nephelitic 
and leucitic rocks, many other alkaline types were explained by the 
assimilation of hydrous sediments, in indefinitely varied mixture with 
one another or with more siliceous rocks or with carbonate rocks. 
During the last four years new field observations and some 
experimental work bearing on the subject have been reported, and 
important papers on general theory as well as on special points have 
been published. A review of these matters and correlated observa- 
tions of older date is the purpose of the present article. A full 
discussion of the origin of alkaline rocks is not attempted, but. 
rather a supplement to corresponding chapters in the writer’s 
Igneous Rocks and Their Origin. After brief discussion of the 
field and chemical studies, Bowen’s petrogenic theory, the strength 
of which is so largely measured by its ability to explain the alkaline 
rocks, will be analyzed in some detail. 
RECENT FIELD OBSERVATIONS 
Many investigators of alkaline rocks still continue to give merely 
petrographical descriptions. Others discuss the origin of the rocks, 
but are content to refer the various types to differentiation without 
giving any adequate idea of what was differentiated. A few writers 
during the last four years have more seriously considered the ques- 
tions of origin, and it is worth while to note their findings. 
Relation of the alkaline and subalkaline suites—From new. 
localities have come proofs of the exceedingly close time and space 
associations of the alkaline (‘‘Atlantic”’) and subalkaline (‘‘Pacific’’) 
eruptives. Among those who have lately laid emphasis on the 
point are Lacroix, Smyth, Cross, Washington, Holmes, Bowen, 
Harker, and the writer.” 
R. A. Daly, Igneous Rocks and Their Origin (New York, 1914), p. 305. 
2 A. Lacroix, Bull. soc. géol. France, X (1910), 91; Comptes rendus, CLV (1913), 
538; C. H. Smyth, Amer. Jour. Sci., XXXVI (1913), 41; W. Cross, Prof. Paper 88, 
U.S. Geol. Surv., 1915, pp. 85, 913 H.S. Washington, Compte rendu, Cong. géol. internat. 
