108 MINERALS AND GEOLOGY 



contain a lower per centage of silica. They are more readily fusible, 

 moreover ; and are decomposed, or at least strongly attacked, by hy- 

 drochloric acid.] 



60. Labradorite or Lime Feldspar: Grey, greyish-white, greenish 

 white, greyish-blue, with frequently reflections of a beautiful blue, 

 green, orange or other colour. Triclinic in crystallization, but rarely 

 occurring otherwise than in cleavable lamellar masses, the cleavage 

 planes, which usually present a delicate striation, meeting at angles 

 of 93 40' and 86 20'. H=6.0 ; sp. gr. 2.662.76. BB, in thin 

 splinters, readily fusible. Decomposed, or strongly attacked, in 

 powder, by hydrochloric acid. Average composition : silica 53, 

 alumina 30, lime 12.5, soda 4.5. This species enters into the com- 

 position of various trappean rocks, and it also forms, both alone and 

 in admixture with other triclinic feldspars, large tnasses of crystal- 

 line structure associated with gneiss and other nietamorphic strata. 

 In this latter condition, it predominates amongst the Upper Lauren- 

 tian or so-called Labrador series of Canada (see Parts III. and V.). 

 Fine examples occur in St. Je'rdme, Morin, Abercrombie and Mille 

 Isles, in the County of Terreboiine, north-west of Montreal ; and in 

 boulders (probably from the above sources) scattered over Grenville 

 Township, on the Lower Ottawa. The Labradorite of these locali- 

 ties is frequently opaque- white on the surface from semi-decomposi- 

 tion or weathering. A pale-blue and greyish variety, without 

 opalescence, occurs in Chateau Richer (Montgomery County), below 

 Quebec. Pale greenish-blue and other opalescent examples have 

 been obtained from boulders in the Townships of Drummond and 

 Lanark, west of the Ottawa ; and a range of feldspathic rocks, pre- 

 senting fine examples of colour-reflecting Labradorite, occurs on the 

 north shore of Laka Huron, east and south-east of French River. 

 The occurrence of Labradorite at the latter locality was first made 

 known by Dr. Bigsby. A granular variety, in which the opalescent 

 tints only shew under the magnifying glass, occurs with scattered 

 pyrites in a vein traversing Laurentian gneiss in the vicinity of 

 Haliburton, Ontario. 



61. Andesite : This is a somewhat doubtful species apparently 

 intermediate in character between Albite or Oligoclase and Labra- 

 dorite. A reddish, feldspathic mineral in cleavable and striated 

 masses, from the Labrador rocks of Chateau Richer, below Quebec, 



