6 
528 A POPULAR EXPOSITION OF THE 
occurs in small quantities in the feldspar bands of the Laurentian 
strata, as in the counties of Terrebonne, Lanark, &c. Also in 
foliated masses in a mixed feldspathic rock, in the parish of Chateau- 
Richer, (Montmorency County,) below Quebec, (T. Sterry Hunt : 
Report for 1854.) 
Wollastonite (Tabular Spar.)—White or light-grey, (rarely red or 
brownish.) Chiefly in tabular masses with fibrous structure. H. 
5:0; sp. gr. 2°77-2°9. Fusible more or less easily. Composition : 
silica 52, lime 48. Found principally in the Laurentian limestones, 
as in the parish of St. Jérome, and in Morin township, Terrebonne 
County. C. E.; in Grenville township, Argenteuil County, and other 
localities. Wollastonite forms also, in union with augite, a distinct 
rock belonging to the Laurentian metamorphic series, (See the 
“ EHsquisse géologique du Canada,” by Sir W. E. Logan and T. Sterry 
Hunt.) 
Orthoclase or Potash Feldspar.—This mineral occurs in white, red, 
pink, light-green, and greyish cleavable masses, and in crystals 
(frequently twins.) of the Monoclinic System, figs. 42 and 43. The 
cleavage planes meet at an angle of 90°. H. 6:0; sp. gr. 2°5-2'6. 
Fusible with difficulty, although the edges of a thin 
splinter become easily rounded. By this character, 
as well as by its lamellar cleavable structure, feld- 
spar may be readily distinguished from quartz. 
Composition, essentially : silica, 64:8 ; alumina, 
Fic. 42. Fig 43. 18-4; potash, 16°8. Feldspar is one of the compo- 
nent minerals of granite, syenite, gneiss and other eruptive and 
crystalline rocks—and, as such, occurs abundantly throughout the 
area occupied by the Laurentian deposits ; and also amongst the 
eruptive masses of the more modern metamorphic region, including 
the district of Montreal, &c. Amongst special localities, we may 
cite the following:—Lanark County, C. W., where the beautiful 
“avanturine” variety termed “ Perthite,” and green and other spe- 
cimens, occur. Grenville, and Chatham, in Argenteuil County: red 
and other crystals in porphyritic trap. Chambly, in the County of 
that name: large yellowish-white crystals in porphyritic trap. The 
Yamaska Mountain; &c. Feldspar yields by decomposition a white 
clay or earthy mass termed “ Kaolin” or “ porcelain clay,” largely 
used in the arts. 
