DESORIPTION of BUILDING STONES. A few of the more prominent classes of building stones will now be briefly described.
Although trap is the strongest of building materials, and exceedingly durable, it is little used, owing to the great difficulty with which it is quarried and wrought. It is an exceedingly tough rock, and, being generally without cleavage or bedding, is especially intractable under the hammer or chisel. It is, however, sometimes used with excellent effect in cyclopean architecture, the blocks of various shapes and sizes being fitted together with no effort to form regular courses. The "Palisades" (the bluff skirting the western shore of the Hudson River, opposite and above New York) are composed of trap-rock. It is much used for road-metal, paving blocks, and railroad ballast.
Granite is the strongest. and most durable of all the stones in common use. It generally breaks with regularity, and may be quarried in simple shapes with facility; but it is ex tremely hard and tough, and therefore can be wrought into elaborate forms only with a great expenditure of labor. For this reason the use of granite is somewhat limited. Its strength and durability commend it, however, for foundations, docks, piers, etc., and for massive buildings; and for these purposes it is in use the world over.
The larger portion of our granites are some shade of gray in color, though pink and red varieties are not uncommon, and black varieties occasionally occur. They vary in texture from very fine and homo geneous to coarsely porphyritic rocks, in which the individual grains are an inch or more in length. Excellent granites are found in New England, throughout the Alleghany belt, in the Rocky Mountains, and in the Sierra Nevada Mountains. Very large granite quarries exist at Vinalhaven, Maine; at Gloucester and Quincy, Massachusetts; and at Concord, New Hampshire. These quarries furnish nearly all the granite used in this country. An excellent granite, which is largely used at Chicago and in the Northwest, is found at St. Cloud, Minnesota.
At the Vinalhaven quarry a single block 300 feet long, 20 feet wide, and 6 to 10 feet thick was blasted out, being afterwards broken up. Until recently the largest single block ever quarried and dressed in this country was that used for the General Wool Monument, now in Troy, New York, which measured, when completed, 60 feet in height by 51 feet square at the base, being only 9 feet shorter than the Egytian Obelisk now in Central Park, New York. In 1887 the
Bodwell Granite Company took out from its quarries in Maine a granite shaft 115 feet long, 10 feet square at the base, and weighing 850 tons. It is craimed that this is the largest quarried stone on record.
In common language, any limestone which will take a good polish is called a marble; but the name is properly applied only to limestones which have been exposed to metamorphic action, and have thereby been rendered more crystalline in texture, and have had their color more or less modified or totally removed. Marbles exhibit great diversity of color and texture. They are pure white, mottled white, gray, blue, black, red, yellow, or mottled with various mixtures of these colors. Marble is confessedly the most beautiful of all building materials, but is chiefly employed for interior decorations.
Limestones are composed chiefly or largely of carbonate of lime. There are many varieties of limestone, which differ in color, composition, and value for engineering and building purposes, owing to the differences in the character of the deposits and chemical combinations entering into them. "If the rock is compact, fine grained, and has been deposited by chemical agencies, we have a variety of limestone known as travertine. If it contains much sand, and has a more or less conchoidal fracture, we have a siliceous limestone. If the silica is very fine grained, it is horn stone. If the silica is distributed in nodules or flakes, either in seams or throughout the mass, it is cherty limestone; if it contains silica and clay in about equal proportions, hydraulic limestone; if clay alone is the principal impurity, argillaceous limestone; if iron is the principal impurity, ferruginous limestone; if iron and clay exceed the lime, ironstone. If the ironstone is decomposed and the iron hydrated, it is rottenstone; if carbonate of magnesia forms one third or less, magnesian limestone; if carbonate of magnesia forms more than one third, dolomitic limestone." The light colored and fine grained limestones are deservedly esteemed as among our best building materials. They are, however, less easily and accurately worked under the chisel than sandstones, and for this reason and their greater rarity are far less generally used. The gray limestones, like that of Lockport, New York, when ham mer dressed, have the appearance of light granite, and, since they are easily wrought, they are advantageously used for trimmings in buildings of brick.