. The Canadian journal of industry, science and art. 432 A POPULAR EXPOSITION OF THE the base or imbedded crystals were of a red colour; but it is now conventionally bestowed on all rocks containing distinct crystals of feldspar or other minerals. Thus, we have porphyritic granite, por- phyritic trachyte, &c. Occasionally, the mica in granite is replaced by talc, giving rise to Talcose Granite. Sometimes, also, the mica dies out, when a granitic mixture of quartz and feldspar results. This has been called Pegmatite. Examples of intrusive granite occur amongst the strata of the Laurentian a
. The Canadian journal of industry, science and art. 432 A POPULAR EXPOSITION OF THE the base or imbedded crystals were of a red colour; but it is now conventionally bestowed on all rocks containing distinct crystals of feldspar or other minerals. Thus, we have porphyritic granite, por- phyritic trachyte, &c. Occasionally, the mica in granite is replaced by talc, giving rise to Talcose Granite. Sometimes, also, the mica dies out, when a granitic mixture of quartz and feldspar results. This has been called Pegmatite. Examples of intrusive granite occur amongst the strata of the Laurentian and Huronian series in the Lake Superior region and on the north shore of Lake Huron, and elsewhere, but apparently in no very prominent masses; although veins composed of quartz and feldspar, or of quartz alone, are of exceedingly common occurrence throughout the entire area occupied by the gneissoid Laurentian rocks. Fig. 53 is a sketch of some quartzo-feldspathic veins in gneiss, near the right bank of the river Severn, C. W. In the more modern metamorphic district south of the St. Lawrence, however, granitic mas- ses (which appear to pass into granitic trachytes or diorites) constitute the Megantic mountains, and occur also in force in Hereford, Stanstead, and other townships of that district. (The localities cited by Sir "William Logan, in his Esquisse Geologique du Canada, comprise : Stanstead, Barnston, Hereford, Marston, Megantic Mountains, Wee- don, Winslow, Stafford, and Lambton.) Syenite.—This eruptive rock is composed of a granitic mixture of quartz, feldspar, and hornblende, the latter being green or black in colour. When mica is also present, the rock becomes syenitic granite; and when the quartz grows gradually less and less abundant, there is a transition into granitic diorite or greenstone. Some syenites are of a red colour from the prevalence of red feldspar, and many syenites are porphyritic. Intrusive syenite occurs amongst the Laurentian rocks in vari
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