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Half way to the head of the lake is a dike having a total width of eight feet, consisting of a central band of segregated quartz, six feet wide, cut by numerous thin sheets of biotite, which probably mark the planes of shearing. The quartz is bordered on either side by a band of orthoclase, one foot in width.
This series, about 20,000 feet in thickness, is, as before stated, unconformable to that last mentioned; it consists in great part of gneiss of a reddish tint with orthoclase feldspar. Beds of nearly pure quartz, from 400 to 600 feet thick, occur in some places. Hornblendic and micaceous schists are often interstratified, and beds of limestone, usually crystalline. Beds of plumbago also occur.
Between these bands of orthoclase and the neighboring amphibolite are narrow bands of schist One hundred feet south of the above point is a second dike having a similar strike and dip and a width of eighteen feet. A third narrow dike, containing small pockets of magnetite, is twenty-five feet south of the second. Only the first is distinguished by the segregation of the quartz.
Ordinary granite, as well as syenite and eurite, usually contains two kinds of feldspar: First, the common, or orthoclase, in which potash is the prevailing alkali, and this generally occurs in large crystals of a white or flesh colour; and secondly, feldspar in smaller crystals, in which soda predominates, usually of a dead white or spotted, and striated like albite, but not the same in composition.
Basalt is the most fusible of volcanic rocks, owing to the augite and magnetite it contains, so that it spreads out with a very slight slope when highly fused. Trachyte, on the other hand, is the least fusible owing to the presence of orthoclase felspar, or quartz; so that the volcanic domes formed of this material stand at a higher angle from the horizon than those of basaltic cones.
The granite of Mourne is peculiar in structure, and differs from the ordinary type of that rock in which the silica forms the ground mass. In the case of the granite of the Mourne Mountains, the rock consists of a crystalline granular aggregate of orthoclase, albite, smoke-quartz, and mica; it is also full of drusy cavities, in which the various minerals crystallise out in very perfect form.
Miascite is one of the varieties of syenite most frequently spoken of; it is composed chiefly of orthoclase and nepheline, with hornblende and quartz as occasional accessory minerals. It derives its name from Miask, in the Ural Mountains, where it was first discovered by Gustavus Rose. ZIRCON-SYENITE is another variety closely allied to Miascite, but containing crystals of Zircon.
The soil on which the apple is mostly grown is largely composed of granitic matter, and is of a sharp, sandy, loamy nature, often of a gritty character. It is usually rich in potash, the predominating felspar being orthoclase, but somewhat deficient in nitrogen and phosphoric acid. It is usually easy to work, of fair depth, and retains moisture well when kept in a thorough state of tilth.
These dolerites are cut through by intrusive syenite, and this syenite, in its turn, is again cut and penetrated by feldspar porphyry, the base of which consists of petrosilex, or a mixture of orthoclase and quartz. All these trap- rocks appear to be of Laurentian date, as the Cambrian and Huronian rocks rest unconformably upon them. General Aspect of Plutonic Rocks. Granite and its Varieties.
A single thickness of blanket is a better mattress than none, but the larger crystals of orthoclase, protruding plentifully, punched my back and caused me to revolve on a horizontal axis with precision and accuracy. How I loved Cotter! how I hugged him and got warm, while our backs gradually petrified, till we whirled over and thawed them out together!
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