70 J. A. Dresser — Stud;/ in the Metamorphic Rocks 



LlTHOLOGY. 



Black (Graphitic) Limestone. — This is a very dark gray, or 

 more frequently, a black impure limestone carrying a large 

 proportion of graphite, which is sometimes so great in amount 

 as to give the rock somewhat of the unctuous feel of that min- 

 eral. It is consequently very soft and brittle. It is usually 

 mnch wrinkled and corrugated by pressure and not infre- 

 quently has a distinct slaty structure developed at high angles 

 to the bedding plane. It contains numerous veins of crys- 

 talline calcite and quartz, in which cases these minerals are 

 intricately associated in the same veins without any dis- 

 cernible arrangement. Some of the veins carry a little pyrite. 



At Melbourne village, opposite the town of Richmond, this 

 rock is marked as fossiliferons on the Montreal sheet of the 

 Eastern Townships map issued by the Geological Survey to 

 accompany the Annual Report of 1894, but no determination 

 of the fossils or indication of their age is recorded except that 

 the notation of the map includes the rock with the 'Farnham 

 Black Slates' of the Lower Trenton formation, D3 a . 



Gray Mica Schist. — This is a schistose rock, usually much 

 wrinkled and contorted, and cleaves very smoothly in the most 

 intricate folds. In color it is a light or greenish gray, weath- 

 ering to dark gray, or brown, tints. 



Under the microscope it appears as a rather fine even-grained 

 and much altered sandstone with a highly developed schistose 

 structure. The grains are both feldspar and quartz and are 

 contained in a micaceous (sericite) cement in which chlorite 

 occurs in varying amounts. A little iron ore is present in 

 small grains, or string-like masses, and also occasional cubes of 

 pyrite of microscopic size. It is an undoubted clastic. 



Black Mica Schist. — By an increase of dark minerals, chiefly 

 iron, and probably by the addition of graphite, the gray mica 

 schist passes into a black schistose rock having a submetallic 

 lustre on its cleavage faces. Microscopically it differs little 

 from the previous rock except in the dissemination of dark 

 grains of the opaque minerals. In reflected light some of the 

 larger can be easily distinguished as pyrite, or a black ore of 

 iron, but others, the smaller and more numerous which are 

 irregular in outline, are thought to be graphite, in part at least. 

 The gravity of the rock is not such as to indicate any notice- 

 able increase in heavier constituents over the preceding variety. 



Occasional inclusions of dark gray or black limestone are 

 found in the black mica schist. They vary in size from mere 

 grains to masses several feet in each dimension. It is difficult 

 to estimate their proportion in the rock, as they agree with it 

 very closely in color and share in its foliation. They are not 



