160 A POPULAR EXPOSITION OF THE 
magnesia, and about 12 to 15 per cent. of water. Serpentine occurs 
in association with the crystalline limestones of the Laurentian 
rocks, as in the township of Grenville, Argenteuil county, C.E., 
where it occurs in disseminated grains; Calumet Island on the 
Ottawa ; the township of Burgess, Lanark County, C.W.; Marmora 
and adjacent townships, with magnetic iron ore; and in other places 
where these rocks prevail. It is met with, however, far more exten- 
sively amongst the altered Silurian strata of the Hastern Townships, 
both alone, and forming, in some localities, especially in the town- 
ships of Oxford and Broughton, serpentine marbles of great beauty. 
Fine varieties of green serpentine occur about Brompton lake, in the 
former of these townships. A tough, fibrous variety occurs in Bolton 
township, Brome County. In Bolton and Ham also, serpentine 
rock, carrying thin beds of chromic iron ore, is met with; and in 
the county of Beauce, this rock contains a bed of mixed magnetic 
and ttaniferous ore, fifty feet in thickness. To these localities must 
be added Mount Albert in Gaspé, where, as described by Mr. Rich- 
ardson of the Geological Survey of Canada, an inexhaustible supply 
of green, brown, and variously striped and mottled serpentine, 
capable of economic employment, occurs in association with chromic 
iron. In its rock relations, serpentine will be discussed more fully 
-in a succeeding part of this Essay. 
Chlorite.—This mineral occurs chiefly in foliated, scaly, and granu- 
lar masses of a dark green colour; or in greenish-grey slaty beds, 
forming the so-called potstone, a name also sometimes applied to 
varieties of steatite. H. 2°0—2°5; sectile; sp. gr. 2°6—2°8. 
Fusible (or fusible on the edges only, in some varieties,) and yielding 
water in the bulb-tube. Composition, essentially : silica 32°5, alumina 
18°5, magnesia 36, water 13: hence, the chloritic potstones differ from 
the workable steatites in containing alumina as an essential consti- 
tuent. In union with quartz, forming chlorite slate, this mineral 
is of common occurrence amongst metamorphic strata. In Canada, it 
occurs chiefly in the altered rocks of the Eastern townships, associated 
with magnetic and specular iron ores, sphene, &c., and with beds of 
dolomite. In this region, as in the townships of Potton, Bolton, &c., 
it is met with also in thick beds of a slaty or more or less compact 
structure, forming an aluminous potstone of good workable quality. 
Chloritic schists, probably of Huronian age, occur likewise, according 
to Sir William Logan, in great force in the valley of Lake Temisca- 
