I30 The Ottawa Naturalist. 



As serpentine is a secondary mineral, that is it has been 

 formed by the decomposition of some constituent of the rock, its 

 origin must always offer a question of interest. This can only 

 be determined by finaing a part of the parent mineral still 

 remaining- in or around it, or by recognizing the crystallographic 

 outline or traces of its cleavage form, in the pseudomorphic 

 serpentine. A careful examination in this case shows the alter- 

 ation to serpentine to be complete. This fact together with what 

 has been said of the outlines of the serpentine areas, precludes 

 all evidence from the first and second sources that have been 

 mentioned. 



The serpentine, however, shows in polarized light series of 

 white lines often intersecting and thus forming what is known 

 as "grating " or " window " structure. 



These lines are narrow bands of fibrous serpentine running 

 along the lines of cleavage of the original mineral whose position 

 and direction they thus indicate. 



In several grains of serpentine these lines are seen to 

 intersect quite regularly at an angle of 120°- 130°, thus strongly 

 suggesting a basal section of hornblende, whose cleavage lines 

 intersect at I24°-I25\ Hornblende is not an unusual source of 

 serpentine although its more common origin is olivine. 



Muscovite appears in several smaller grains, sometimes en- 

 closed in the serpentine or calcite, but more frequently lying be- 

 tween them. 



A few grains are present possessing a bright metallic lustre 

 in incident light, and surrounded by yellowish-brown rims. 

 They are probably pyrite. Magnetite is also probably present. 

 All, however, are so small in size and so few in number as to be 

 relatively unimportant. 



With regard to the origin of this rock, two alternatives 

 present themselves : 



(i) If the inclusions before mentioned could be accepted as 

 evidence of organic origin, the calcite would be regarded as a 



