76 MINERALS AND GEOLOGY 



in a copper-ore vein, on Lot 8, Range 1, in Melbourne Township. 

 Small but very symmetrical octahedrons are obtained occasionally from 

 the thick-bedded Trenton Limestone on the Bay of Quinte', near Belle- 

 ville. Cubes, pentagonal dodecahedrons, and other crystals, occur in 

 many of the veins and gneissoid rocks of Madoc, Elzevir, Tudor, &c. 

 Occasionally also, well crystallize examples are seen in the veins, and 

 also in the trap dykes, of Lake Huron and Lake Superior; and small 

 brilliant crystals occur in the white compact trachyte of Montreal. 

 Finally, it may be mentioned, without attempting however to name 

 all the localities of this mineral in Canada, that peculiar nodular or 

 concretionary masses occur in the shales of the Island of Orleans, 

 and elsewhere near Quebec ; and in the more modern bituminous 

 shales of the Portage Group, at Cape Ibberwash or Kettle Point, 

 Lake Huron. 



21. Prismatic Pyrites or Marcasite (Radiated Pyrites, Cockscomb 

 Pyrites, <fec. ) : Light brass - yellow ; 

 Rhombic in crystallization, the pris- 

 matric crystals mostly in radiated aggre- 

 gations, or united in rows, as in Fig. 42. 

 Composition and other characters as in 

 the common or cubical pyrites, the two FIG 42. 



minerals thus presenting an example of Dimorphism i.e., the assump- 

 tion of two distinct sets of forms by the same chemical substance. 

 The prismatic species is especially subject to decomposition, yielding 

 iron vitriol. 



The occurrence of prismatic pyrites in Canada was first made 

 known by the author, who met with it in 1865 in a quartz vein 

 (carving copper pyrites, galena, heavy spar, &c., together with ex- 

 amples of cubical pyrites), in the remote Township of Neebing, a few 

 miles east of the Kaministiquia River, on the north west shore of 

 Lake Superior.* Other examples have come under his notice on 

 subsequent visits to this district, from some of the silver-bearing 

 veins of Thunder Bay ; and he has obtained recently a large and fine 

 specimen from a vein in Laurentian rock in the Township of Hinchin- 

 brook, in Frontenac County. Many of the spherical masses of 

 pyrites with radiated structure and crystallized surface, it should be 

 observed, though commonly referred to Marcasite, belong really to 

 the cubical species. 



* Lot 25. Con. 5. Canadian Journal, 2nd Series, Vol. X., 408. 



