316 Canadian Record of Scieiice. 



By the aid of the microscope the constituents of the 

 rock are seen to be as follows : 



I. Essential. — 1. Primary— Hornblende. 



Feldspar. 

 2. Secondary — Calcite. 

 Chlorite. 

 Serpentine (?) 



II. Accessory.-l. Primary-|^^''g"etite. 



I Apatite. 

 2. Secondary — Leucoxene. 



Hornblende is in very distinct idiomorphic crystals, 

 often having a slender columnar form, and is the most 

 prominent constituent of the rock. It is brown in color 

 and pleocliroic with b nearly = C, the scheme of absorption 

 being 0'b>>a. C and b = dark brown, and a, yellowish 

 brown. The greatest angle of extinction that was meas- 

 ured, c/\C, — 17°. A number of smaller crystals are also 

 present, but it is not definitely ascertained whether they 

 represent a separate generation, i.e., that they crystallized 

 at a different period of the solidification of the rock from 

 the larger hornblendes, or not. 



Feldspar appears usually in lath-shaped or slender sec- 

 tions, which are generally unstriated by the polysynthetic 

 twinning of plagioclase, though many are twinned once. 

 Some extinguish nearly or quite parallel to the longer axes, 

 others at angles as high as 80°. The feldspars often show 

 an approach to a radial arrangement, and are less dis- 

 tinctly idiomorphic as well as less abundant than the 

 hornblende. 



Calcite, either alone or more frequently associated with 

 other secondary minerals, forms numerous irregular 

 masses in which crystals of feldspar are sometimes 

 imbedded. After hornblende and feldspar it is the most 

 abundant constituent. While presumably of secondary 

 origin, no remnants of any ndneral from which it has 

 probably been derived have been found in it. 



