PETROGRAPHICAL NOTES. 93 



" darkened at borders, isotropic, often decomposed with formation of 

 ''fibrous zeolites; rectangular meshwork of dust lines occasionally 

 " shown, 



"Rounded masses of tufted zeolites with clear apatite crystals 

 " probably represent patches where sodalite was once concentrated. 

 " The products of decomposition include caltite. 



" Much of the colourless groundmass is decomposed by hydrochlo- 

 ric acid with formation of gelatinous silica in which the insoluble 

 " granules (aegerine, etc.) are imbedded. Treatment of the powdered 

 " rock with nitric acid is attended with effervescence, and the solution 

 " gives reactions for chlorine (strong), sulphuric acid (very faint), 

 " alumina (strong), and phosphoric acid (strong). 



" Opaque iron ores present only in very small quantities and as 

 " very minute grains. 



" The rock appears to resemble a tinguaite from the neighbourhood 

 "of Montreal. (Rosenbusch, Mass. Gest., 1896, p. 483)." 



The specific gravity of the rock is 2"6g. 



At the same locality is found a dense nearly black basaltic rock 

 (No. 13,804), containing plagioclase felspar, pale red brown augites 

 and a large amount of iron ore. The specific gravity of this rock is 

 3'23. It approaches some of the Deccan traps in composition. The 

 relations of this rock with the tinguaite could not be made out, as the 

 junction is concealed by sand. 



( 93 ) 



