604 THE JOURNAL OF GEOLOGY. 



foyaite, described by Prof. Rosenbusch and Dr. G. H. Williams 

 from the phonolite massif of the island of Fernando de Noronha, 

 whose eruption is presumed to be of much later date than that of 

 the continental centers above described. Whatever may be the 

 explanation of the assumption of the leucite form, without the 

 substance of that mineral, by these inclusions at Caldas and 

 Tingua, this phenomenon may also be cited as an evidence of 

 consanguinity. Confirmatory evidence is afforded by the inti- 

 mate association of typical leucite and nepheline rocks in the 

 Caldas massif, and perhaps also by the occurrence in Paraguay. 



The evidence of consanguinity of the augite-syenite type with 

 those bearing nepheline is almost equally complete. At Tingua, 

 where there is an apparent lack of this type, a single large frag- 

 ment was found as an inclusion in foyaite. At Jacupiranga, a 

 direct passage by disappearance of nepheline, from foyaite to one 

 phase of augite-syenite could be traced, while other phases of the 

 same type were found associated with foyaite in the same dyke or 

 boss. Most interesting is the association of this type at Jacupiranga 

 and Ipanema with nepheline rocks more basic than the foyaites and 

 phonolites, such as the jacupirangites and phonolitic nephelinites, 

 in the latter of which it occurs as an inclusion or segregation. In 

 this connection it is interesting to note the tendency, rare among 

 the orthoclase rocks, of this type to present olivine as an acces- 

 sory element. 



Still more interesting, though less conclusive, are the indica- 

 tions of consanguinity of foyaite with a group of plagioclase rocks 

 hardly, if at all, distinguishable from those of entirely different 

 genetic relations. At Cabo Frio the appearance is certainly that 

 of segregations of a plagioclase rock in the midst of foyaite, though 

 farther investigation is desirable. At Jacupiranga the two types 

 not only occur in the same dyke or boss, but nepheline has 

 actually been observed as a rare accessory in the gabbro-like 

 rock. The appearance of plagioclase in the pseudo-leucite crys- 

 tals of Tingua bears on the same question, as does also the appear- 

 ance in a large collection of phonolite from Fernando de Noronha 

 of a single specimen of an andesite-like rock, which unfortunately 



