SOME UNUSUAL ROCKS FROM MAINE 185 



green variety is developed. The olivine contains numerous mag- 

 netite inclusions, usually very irregular in form, and distributed 

 principally along the cracks; some of the smaller ones show den- 

 dritic forms. All are probably of secondary origin. 



Hypersthene occurs in irregularly bounded grains. Pleochroism 

 strong, a = pale salmon-pink, b = pale yellow, r = pale green. It 

 occasionally incloses both olivine and biotite. In a few places 

 it shows slight alteration to hornblende. 



Biotite is abundant and quite strongly pleochroic, colorless to 

 pale yellow parallel to a, yellowish to hght brown parallel to b or 

 r; it seems to be in small part a product of hornblende alteration. 



A micaceous mineral showing only feeble pleochroism and inter- 

 ference colors never above yellow of the first order is probably 

 intermediate in character between chlinochlore and pennine. It 

 appears to be uniaxial and optically positive, with the slow direction 

 parallel to the micaceous cleavage (i. e., perpendicular to r). The 

 pleochroism is hght green for rays vibrating parallel to the base, 

 and colorless for rays at right angles to this. 



Magnetite and olivine were the first minerals to crystalhze, fol- 

 lowed by hornblende, hypersthene, and biotite, the last three being 

 about contemporaneous. The elongation of many of the magne- 

 tite inclusions parallel to the cleavage planes of the inclosing horn- 

 blende, shows either some secondary magnetite crystallization, 

 or else a partially contemporaneous crystalhzation of hornblende 

 and magnetite. 



Megascopically, the Maine rock differs from the type rock of 

 Stony Point, mainly in showing a much larger amount of biotite. 

 Microscopically, the same difference is apparent, and it is also 

 seen that the colors of the hornblende are much paler in the Maine 

 specimen; in the Stony Point rock this mineral is a dark reddish 

 brown. Some of the Stony Point specimens show feldspar as a 

 subordinate constituent, but here it is wholly absent. The relative 

 proportions between hornblende and olivine seem to be about the 

 same in the two rocks. No chemical analysis was made of the 

 Maine rock, but it is probable that it will fall within the same 

 order as those already analyzed. 



The geologic age of the rock here described is uncertain, because 



