and Geology of Lake Ontario. 265 



round-backed massive hills (lower end of Crow Lake), and is 

 pure white, varying in its texture in patches from the compact 

 to the saccharine and largely crystalline form. 



I doubt not but that this rock is in very large quantities in 

 these districts. I have crossed two large tracts of it on the 

 Ottawa River, one being twenty miles broad. Another is met 

 with on the western branch of that river, some miles east of 

 Lake Nipissing. The north shore of Lake Ontario and the 

 south side of Lake Simcoe present many large boulders of it. 



The sienite forms broken sterile ridges, and is composed 

 principally of translucent gray felspar, in rather large facets. 

 The hornblende is in pale green and small-crystallized frag- 

 ments, varying in quantity, and prevailing most near Foster's 

 ore bed *. The little quartz it contains is colourless. Epidote 



* There are numerous beds of ore in this vicinity, but the principal one 

 is at the upper end of Crow Lake, at the water's edge. It is in the face of 

 an acclivity about fifty feet high, covered with boulders of quartz, coloured 

 by epidote and charged with magnetic iron ore. The whole eminence is 

 probably a mass of ore, but at present the exposed portions are only sixty 

 feet broad by ten in height. It is traversed by confused fissures, and is 

 massive, jutting out in very large angular wedges. No rock appears in con- 

 nection with it, being concealed by debris and vegetation. The ore is 

 the granular magnetic, containing, however, much sulphur. Foster's bed, 

 four miles and a half east of Marmora Works, and in the woods, seems 

 exhausted. I could find nothing in the large excavation made in the sienite, 

 but a few loose masses of ore, large fragments of calcspar filled with octo- 

 hedral crystals of iron ore, and garnets. I also met with a minutely blended 

 compound of hornblende, quartz, and garnet, having superimposed a new 

 crystalline form of the first-mentioned mineral. Dr. Troost of Philadelphia 

 has described it in a recent Number of the Journal of the Academy of Na- 

 tural Sciences of Philadelphia, in the following words : 



" Amphibole.— The specimen now under consideration, was at first very 

 enigmatical. I was entirely misled by its crystalline form, so widely devi- 

 ating from those usually presented by amphibole. In all the crystals of this 

 mineral hitherto described, the faces M of the primitive form (Haliy) com- 

 pose the greater part of the prism, and the summits have generally two or 

 more faces. I was therefore much surprised to find the characters and 

 composition which distinguish amphibole combined with the crystalline form 

 now to be described. It is a rectangular prism, terminated in some of the 

 crystals by an inclined plane, and in a few others by a dihedral summit. 

 These crystals, which have a greenish and sometimes a black colour, with 

 a rough surface, are divisible ))arallel to the four edges of the prism, forming 

 the rhoniboidal prism of the amphibole, the inclined planes forming an 

 angle with one of the sides, of 105° 11', and must of course be the face /; 

 (see Traile de Miner, dc Haiiy. Atlas, pi. 64) so that we have 1 G 1 1 H 1 E ; 



X . s . I 

 and it approaches therefore to the trinnilaire of Haiiy, the faces M having 

 entirely disappeared : the decrement which forms / has place sometimes on 

 the two angles forining the dihedral sunniiits ; but the greatest part of the 

 crystals on our specimens, liaving but one inclined plane, are the result of 

 the decrement only on one of the angles." 



N.S.\o\.5. No. 28. ^j«7n829. 2M abounds, 



