OF CENTRAL CANADA PART II. 



107 



in calcite veins. Pale-red and other varieties are found in the 

 Ottawa region, especially in the phosphate deposits. Orthoclase 

 occurs also in the metamorphic strata south of the St. Lawrence, 

 as in veins cutting altered slates in the townships of Inverness, 

 Leeds, and Sutton ; and it is likewise present in many of the eruptive 

 rocks of this district, notably in the porphyritic trachyte of Chambly, 

 and in the trachytes of Montreal and Brome. These varieties, ac- 

 cording to Dr. Sterry Hunt's analyess (Report: 1863, p. 476) con- 

 tain nearly equal amounts of potash and soda. Orthoclase, in com- 

 mon with other feldspathic silicates, yields by atmospheric decompo- 

 sition, a white earthy clay, largely used, under the term of Kaolin, 

 in the manufacture of porcelain. 



58. Albite or Soda Feldspar : White, red, greyish-white, &c., 

 sometimes with pale-blueish or pearly opalescence. Triclinic in 

 crystallization, but occurring commonly in lamellar masses, readily 

 cleavable in two directions under angles of 93 36 v arid 86 24\ 

 One of the cleavage planes usually exhibits a delicate striatiou. In 

 other respects, Albite closely resembles Orthoclase. H = 6.0 ; sp. 

 gr. 2.55 2.65. Average composition : silica 68, alumina 20, soda 

 (with trace of potash, &c.) 12. Albite is a constituent of many 

 trappean rocks, and it occurs also in certain granites and syenites, 

 and in various metamorphic strata. An opalescent variety, known 

 as Peristerite, occurs in the township of Bathurst (Lot 1 9, Con. 9), 

 and also on the north shore of Stony Lake, in Burleigh. A white 

 variety in cleavable masses of considerable size forms the feldspathic 

 portion of certain granitic and gneissoid rocks of the more northern 

 districts of the county of Ottawa. Fine crystals are also said to 

 occur in a vein on Lake Massawippi (Stanstead), in the metamorphic 

 region of the Eastern Townships. 



59. Oligodase : White, greenish, pale-grey. Triclinic in crystal- 

 lization, and closely allied in all its characters to Albite, but contain- 

 ing a somewhat smaller percentage of silica. The cleavage planes 

 meet at angles of 95 50' and 86 10'. Occurs in Canada, according 

 to Dr. Sterry Hunt, associated with black amphibole in the eruptive 

 mass of Mount Johnson, in the district of Iberville, near the east 

 shore of the River Richelieu. 



(6) GROUP OF CALCARBO-FELDBPATHIC SILICATES. 



[The minerals of this group are very closely related to those of 

 the preceding division, but they are essentially lime-holding, and 



