178 PROCEEDINGS OF SECTION C. 



arranged in directions which are in a general way perpendicular to 

 the directions of the veins. 



To the naked eye little else than diopside is visible in the bulk 

 of the rock mass. Grains and aggregates of garnet and vesuvianite 

 may at times be detected, and sometimes irregular patches of apple- 

 green to yellowish serpentine. With the latter there is usually 

 chromiferous magnetite of rhombic dodecahedral habit. Occasional 

 specks and films of pyrite, chalcopyrite, galena and blende are 

 visible. 



In thin section the main mass of the normal rock is seen to be 

 built up of hypidiomorphic granular diopside, with greenish-yellow 

 garnet and vesuvianite. The diopside is the earlier mineral to 

 crystallise. The serpentine appears to be truly authigenic. It has 

 an ill-defined internal structure as revealed between crossed nicols 

 and surrounds the magnetite and garnet. 



(b). Chlorite Rock. — ^This group comprises several different 

 members, the outward appearance of which is somewhat variable. 

 They possess a habit which is sometimes massive and sometimes 

 schistose, and they are disposed in veins which are closely associated 

 with the diopside rock at more than one point in the vicinity of the 

 Heemskirk granite massif. The most prominent constituent is 

 chlorite, the hexagonal plates of which are at times as much as two 

 inches in diameter. The colour is a rich green in unweathered 

 specimens. The serpentine in the rock varies in colour from olive 

 green to pale green, and is disposed in veins or throughout the mass 

 of the rock surrounding the other constituents. A light greenish to 

 yellowish brown mica — probably phlogopite — is a prominent con- 

 stituent of certain bands of the rock, and the plates of this mineral 

 are sometimes as much as an inch in diameter. They are difficult 

 to distinguish macroscopically from the chlorite in many cases. 

 Greenish or yellowish vesuvianite is sometimes visible to the naked 

 eye, and garnet has been seen in clear hyacinth red trapezohedra. 



The microscopical characters of these rocks vary considerably' 

 The prominent constituent — chlorite — is not constant in character- 

 Its colour is usually very pale green to very pale brown, according 

 to the direction of the vibration of the transmitted light. The 

 polarisation colours and optical character measured with respect to 

 elongation are most often those of clinochlore. Yet, intergrown 

 with this member of the chlorite family, or occurring in separate 

 crystals, is another of the chlorites, probably pennine, with deep 

 Berlin blue interference tints and positive elongation. Diopside 

 occurs in small disseminated idiomorphic crystals, or aggregates of 

 crystals, with hypidiomorphic outlines arranged in bands. The 

 serpentine possesses no constant characteristics of internal struc- 

 ture. Vesuvianite is abundant in almost every variety. It is 

 usually granular or euhedral, and shows the characteristic zoned 

 and segmental structures. In one type it assumes a skeletal form 

 with quadratic outlines being intergrown with optically continuous 

 chlorite. The mica has ragged outlines. The normal order of 



