[HOWARD] SOME OUTLIERS OF THE MONTEREGIAN HILLS 59 



arranged in clusters about these groups of augite crystals and as sprays 

 connecting the grains. 



Judging from the single individual noted above, it appears as 

 if the augite was Ojriginally rich in titanium and iron. These con- 

 stituents were leached out from the mineral, the former with lime, 

 and recrystallized along certain indefinite lines within the crystal. 

 It appears, then, that the crystals were resorbed in a solution rich in 

 lime and alkalies which recrystallized, on cooling, to biotite and meli- 

 lite, leaving a few remnants of the original crystal untouched. 



Chrysolite also occurs in comparatively unaltered grains up to 

 0.5 mm. in length and in groups of partially resorbed individuals. The 

 resorption phenomena noted above are also present in the case of 

 chrysolite excepting for the formation of perovskite and iron ore. 



It thus appears as if the original magma crystallized, partly at 

 least, as augite and chrysolite. These crystals were partly resorbed 

 by a magma rich in lime and the alkalies, especially the former, 

 resulting in the formation of a later group of minerals consisting of 

 biotite, melilite, monticellite, and probably magnetite and perovskite, 

 although these last minerals may have been, to some extent, the first 

 products of crystallization of the magma. 



Biotite is the most abundant constituent of the rock and occurs 

 in irregular flakes and occasionally rounded grains. The rounded 

 grains are comparatively free from iron ore and perovskite, and may 

 have been primary along with the augite and chrysolite. The flakes are 

 associated with melilite and iron and titanium minerals and are un- 

 doubtedly of the second period of crystallization. These flakes are 

 about 0.2 by 0.5 mm., and in places occur in an irregular congregation 

 mixed with perovskite and magnetite. Where associated with melilite 

 there is an incipient flow structure as noted above. 



Melilite occurs in laths with dimensions of about 0.02 by 0.05 mm. 

 and is associated with the biotite as noted above and also forms a large 

 proportibju of the groundmass It is characterized by its low bire- 

 fringence and indefinite optical character. The laths are zoned 

 longitudinally, the outer zones having the lowest birefringence. The 

 basal cleavage is indiscernible. 



Monticellite is present in very small amount and usually occurs 

 as widely scattered individuals, not in optical continuity. The 

 resorption rims about the chrysolite are not so conspicuous as in the 

 principal type described above. 



Magnetite and perovskite occur in minute grains and very thin 

 plates, the latter usually forming squares and octahedra. 



