MINERALS AND GEOLOGY OF CANADA. 121 
stove-doors, &c., in the townships of North and South Burgess, C. W. 
Also in Grenville and the “ Augmentation’ of that township in C. E. 
(f). Ornamental Feldspars :—These comprise, the Labradorite of 
Abercrombie township, C. E.; the Peristerite (an iridescent variety of 
Albite) found in the townships of Bathurst and Burleigh, C. W.; and 
the Perthite (an iridescent Orthoclase,) of the township of Burgess. 
See Parr II. The two latter varieties were first made known (as 
occurring in these localities) by Dr. James Wilson of Perth. 
(g). Marbles :—The principal marbles of Laurentian age occur at 
the following localities: Arnprior, MacNabb township (grey, striped) ; 
Grenville township (white with yellowish specks of serpentine, or 
yellowish-white) ; Augmentation of Grenville (white with pale green 
spots of serpentine) ; Elzevir township, C. W., (white but of somewhat 
coarse grain); Barrie township, at Lake Mazinaw, &c., (a crystalline 
dolomite, pure white, and of saccharoidal texture). 
(2). Sulphate of Baryta :—This substance, used as a paint material 
or substitute for white lead (see Part II.), is found in considerable 
quantities, in connexion with Laurentian rocks, in the townships of 
Lansdowne, Burgess, Bathurst, and Dummer, in Canada West, where 
it occurs in the form of veins which often contain galena. It is found 
still more abundantly on Lake Superior, but in rocks of another age. 
(2). Millstones :—The intrusive mass of syenite in the township of 
Grenville, C. K., (described under the head of “ Eruptive Rocks” 
above) is associated with some remarkable veins of chert (a variety of 
quartz) from which good millstones have been manufactured. These 
veins are regarded by Sir William Logan as veins of segregation; and 
it is considered probable that the siliceous matter of which they con- 
sist may have been derived from the decomposition of the feldspar in 
the adjoining mass of syenite. The feldspar is said to be converted 
into kaolin for a considerable distance on each side of the chert. 
5. Area of the Laurentian Rocks :—As shewn by the shaded 
surface in the accompanying map, (figure 154), the Laurentian strata 
may be regarded as constituting from the coast of Labrador, the whole 
ef the north shore of the Saint Lawrence to within a short distance 
of Quebec (Cape Tourmente)—a few isolated and narrow strips of 
Lower Silurian strata (made known by the Geological Survey) alone 
intervening between these rocks and the waters of the Gulf or river. 
These outlying patches occur on the north shore of the Straits of 
