114 R. A. DALY ORIGIN OF THE ALKALINE ROCKS 



phonolite, and nephelite syenite of Cripple Creek. The alkaline fractions 

 of the differentiation were, on this view, segregated through the influence 

 of the juvenile gas in the same manner as that postulated when the 

 carbon dioxide of absorbed limestone segregates the alkaline elements in 

 basalt. Similarly, the phonolites and allied types of many volcanic 

 islands (Hawaii, Kerguelen, etcetera,) may owe their origin to juvenile 

 carbon dioxide, but in no case is it possible to exclude the possibility that 

 marine limestones underlie the respective volcanoes and furnished resur- 

 gent carbon dioxide to the magmas. 



These speculations have little other value than that they show the inad- 

 visability of trying to explain all alkaline rocks in the same way. How- 

 ever, most of the theoretical suggestions of this paper may be generalized 

 as a plea for the recognition of magmatic gases, largely of resurgent 

 origin, as powerful agents in the segregation of alkaline magmas from 

 the subalkaline. The process represents a special case in the differentia- 

 ting effects of the "fluides mineralisateurs." The writer is inclined to 

 go further than Michel Levy and other advocates of this theory and defi- 

 nitely to coordinate most of the alkaline rocks with syntectic magmas 

 composed of subalkaline magmas and calcareous sediments. 



General Conclusions 



The results of this study belong to two different orders. In part they 

 are clearly facts, restated or newly stated and independent of theory; in 

 part the results are hypothetical, and the value of these depends on their 

 finding position in a stable petrogenic theory. 



Among the facts needing emphasis in a general treatment of the alka- 

 line rocks are the following : 



1. The alkaline rocks are seldom, if ever, found without associated 

 subalkaline rocks. Of the latter those derived from basaltic or gabbroid 

 magma are the types most constantly associated. 



2. Either as individual masses or in total volume the visible alkaline 

 bodies are incomparably less important than the subalkaline bodies. The 

 ratio of the total volumes is in the order of magnitude of one to one hun- 

 dred. This ratio applies very nearly to the Atlantic basin as well as to 

 the Pacific basin. As the Pacific basin is being explored, more and more 

 alkaline masses are discovered. The division of igneous rocks into Atlan- 

 tic and Pacific branches, as advocated by Becke, Harker, Prior, and 

 others, is not warranted by the facts of distribution, and is not so safely 

 made as the division into alkaline and subalkaline branches. 



