; Faikbanks.] 



Geology of Point Sal. 



37 



hornblende, to the diabases. The hornblende, augite-bearing rocks 

 he describes under the term teschenite, although at the same time 

 expressing the opinion that they never contained nepheline and 

 should not be referred to the theralites but to a group intermediate 

 between the diabases and the diorites. Rosenbusch * would refer 

 •those varieties of rock earlier termed teschenite to the diabases in 

 which the evidences for the original presence of nepheline is not 

 -clear, while those in which nepheline exists or probably existed, he 

 would retain under the original name and classify them with the 

 theralites. Rhorbach f could find no nepheline in the rocks studied 

 by him, and intimates that apatite has been mistaken for nepheline. 

 He says, "All the rocks of this group are characterized by the pres- 

 ence of analcite and other zeolites " — that the feldspars have a ker- 

 nel of anorthite, and a rim of oligoclase. An analysis of horn- 

 'blende intergrown with augite is given which shows no alkalies. In 

 some of the hornblende three per cent of alkalies were found, which 

 Rosenbusch thinks plays the part of the sgirine in the Montana 

 rocks. 



MacPherson % says of some rocks of Portugal, which he classes 

 with the teschenites, that the analcite occurs in the same manner as 

 quartz in granite, and that it appears to be infiltered into all the 

 elements of the rock, especially into the feldspars. Crystals of 

 analcite appear which are elongated in a manner which seems to 

 correspond to nepTieline. He believes that the nepheline is inti- 

 mately united with the analcite. Of another occurrence (Forte de 

 Alquiedam), " The hornblende disappears wholly, and the pyroxene 

 takes on a diabasic character. The remainder of the rock is formed 

 -of crystals of feldspar and analcite." The analcite is spoken of in 

 such a manner as to convey the impression that it has crystal 

 boundaries, and unless occurring in cavities must have replaced some 

 primary constituent. In all the discussions over the teschenites 01 

 Europe no writer seems to have thought it possible that the analcite 

 could have been introduced after solidification. Although in many 

 cases its amount seems to be large, those who reject the view of its 



* Mikroskopische Physiography, 2d edition, p. 251. 



fMin. u. petr. Mitth. VII, 1886. 



% Bull. Geol. Soc. de France, 1882, p. 292. 



