264 FINLAY 



slightly clouded over by the products of alteration. Occasional 

 Carlsbad twins are noted. This feldspar frequently surrounds 

 large portions of the nephelite. 



The substance of the nephelite is quite fresh. Its outlines 

 tend to be rectangular. The cleavages parallel to the base and 

 the prism are at times developed and the extinctions are parallel 

 to these directions. Transparent microscopic crystals are pres- 

 ent as inclusions in the nephelite, and surrounding it a secon- 

 dary mineral, which is usually referred to cancrinite on account 

 of its low index of refraction and high interference colors, is 

 commonly developed. 



Hornblende, the most abundant constituent of the rock, is the 

 only mineral which has an automorphic habit, excepting the 

 apatite. The unit prism and the pinacoidal planes, in the zone 

 parallel to the c axis are well developed. The crystals are 

 pleochroic from yellow to seal brown. The absorption is 

 strong. Twins are not rare. 



The augite in rude prisms and aggregates of grains is pale violet 

 or greenish, with borders of deeper green from the coming in 

 of the aegirite molecule. Intergrowths with amphibole are com- 

 mon. The augite encloses grains of titanite, and apatite needles. 



Titanite occurs sporadically, in patches which are sometimes 

 1.5 mm. long. (See PL X, fig. i.) The magnetite is in the 

 usual grains with purple black luster. Apatite is very abundant 

 in short stout crystals with its basal sections perfect hexagons 

 charged with irregular dust inclusions. Some minute needles 

 of epidote were observed. 



The order of crystallization appears to have been as follows : 

 First apatite, magnetite and titanite. Then hornblende and 

 augite often enclosing the amphibole. The above minerals are 

 frequently grouped together in such a manner, however, as to 

 make it plain that their growth must have been in large measure 

 simultaneous. After the dark silicates nephelite followed, and 

 the feldspar came last. 



{d) Mesa Verde Type. Basic Fades. 



This variety of the nephelite syenite occurs closely associated 

 with the Mesa Verde type in the same locality on the Baril 



