664 J- S. L. VOGT 



see in a later paper, there results from this process, as a rule, after 

 repeated crystallization-differentiations, the anchi-monomineral 

 magmas (for example, anorthosite, dunite) , where the original quan- 

 tity of the light volatile compounds in the parent-magma must 

 be considerably diluted. 



By the segregation of the anchi-monomineral magmas, the light 

 volatile components, so far as they do not escape, will remain in 

 the rest-magma. Extensive crystallization-differentiation results 

 in anchi-eutectic magmas (most gabbros, norites, syenites, granites) 

 and as the final product of the differentiation running in the anchi- 

 eutectic direction are brought out the granitic magmas. 



Consequently, we must a priori presume that the light volatile 

 components on an average will be in the smallest quantity in the 

 anchi-monomineral magmas which must have been "dry" or 

 "almost dry melts." A somewhat higher percentage may generally 

 occur in the anchi-eutectic magmas and indeed especially in the 

 granitic magmas. And in the last ones result, as the final solution 

 at a very great depth (after Th. Vogt) where the light volatile com- 

 ponents cannot, or can only in part, escape the granite pegmatitic 

 magmas where we may expect a relatively extensive concentration 

 of the volatile components. 



As support to this theoretical deduction we shall first point 

 out that miarolitic druses, according to my own field observations, 

 generally are completely lacking in anorthosites, dunites and 

 petrographically related rocks. On the other hand, they are 

 very common in many granites, quartz-syenites, etc., and in the 

 miarolitic druses we often find, as well known, a supply of 

 pneumatolytic minerals proving that these druses must have been 

 genetically connected with the volatile components. 



Further, according to my own field observations, tourmaline 

 and other pneumatolytic minerals are completely or almost com- 

 pletely wanting in the Norwegian massives of anorthosite and also 

 in the numerous but certainly, as a rule, very small massives of 

 peridotite. By far the most magmatic-epigenetic (pneumatolytic, 

 pyrohydatogen, and hydrotermal) ore deposits are connected with 

 acid or intermediate igneous rocks (granite, quartz monzonites, 

 etc.). These ore deposits are, in relation to the extension of the 



