134 Murgoei — Genesis of Riebeckite and Riebeckite Rocks. 



together, forming, by their uniting cores, one single large mass 

 of eruptive rocks.* In this zone, granites (soda-granites, nord- 

 markite, and quartz syenite) microgranites and granite porphy- 

 ries (granophyre and paisanite) and typical quartz and ortho- 

 clase porphyries are found together in the same or neighboring 

 localities. One may remark, according to the present expo- 

 sures and topography of these rocks, that the porphyritic 

 masses,' with or without riebeckite, occupy a larger area at the 

 surface than the granite (in the proportion of 3:1) ; the region 

 is much eroded, the layers are almost vertical and the porphy- 

 ritic facies occurs in the western part of the granite zone. 

 In this case the porphyritic rocks can not be regarded only as 

 marginal facies of the granite massif. On the other hand, the 

 various rocks with riebeckite form large streaks and patches 

 {scJilieren) mixed at random in the massives, with similar 

 masses without riebeckite, but very acid and poor in black 

 constituents. Some masses, especially those of more basic 

 character, were obviously homogeneous and polygeneous 

 inclusions. Although there are many quarries in the two hills 

 of Jacobdeal and Piatra rosie, which furnish exposures, dike 

 rocks of pegmatitic, aplitic or lamprophyric characters could 

 not be found. In one place a rock of the type of nordmark- 

 ite occurs in such a manner that it might be regarded as a dike 

 terminating abruptly upwards; the same rock, however, occurs 

 in the neighborhood as polygeneous inclusions. 



Owing to the absence of obvious dikes, it is impossible to 

 determine the order of the ascension and consolidation of the 

 magmas forming these various rocks. Their occurrence and 

 structure, their study by chemical and petrographical methods 

 and the relations between them, reveal to us only local phe- 

 nomena which occurred during the consolidation of the large 

 molten mass. 



It is well known what a tendency the alkali magmas have to 

 differentiate and especially in massives of sodic rocks ; this fact 

 can be very well confirmed, as shown by numerous researches. 

 This phenomenon, often described in the alkali rocks of the 

 trachyte syenite series (especially in nephelite syenites), is also 

 mentioned in massives with riebeckite rocks of the granite- 

 rhyolite series, when studied over large areas. There might 

 be cited the classic researches by Brogger (Christiania region), 

 Tenne (Yemen), Washington (Essex County, Mass.f ), Lacroix 



* See the geological map by E. Pascu, Moniteur du Petrole roum. 1904. 

 Bucharest. 



f In the neighborhood of Boston, "the glaucophane granite" studied by- 

 White has been determined by Washington as riebeckite granite (Journal 

 of Geology, vol. vi, No. 8 and foi., 1898-1899), and among the siDecimens 

 which I possess through the kindness of Prof. Kemp, I was able to distinguish 

 riebeckite granophyre, paisanite, interesting inclusions, etc. Even White 

 described gradual variations of structure and composition in one and the 

 same massif. Proc. of the Boston Soc. of Nat. Hist., 28, No. 6, 1897. 



