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rocks, sand, limestones, silica, building, stone and granites

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QUARRYING. Although there are at this time in the United States about 3,000 quarries in operation, with an annual product valued at above $75,000,000, the quarrying industry has not kept pace with modern tendency and prog ress toward cheaper production. In building operations revolutionary changes have come about in the last few years in the erection of steel buildings and the manufacture of terra cotta and clay products, while has been., generally speaking, stationary. The nat ural .result of this has been a large increase in the use of the cheaper substitute materials for ,general bridge and building work, where the naturalreference would have been for stone as an and more permanent material, but for its prohibitive cost. As the rapid increase in the use of these other building materials is the direct result of the use of modern methods and machinery to the elimination of hand labor in the greatest degree, it 'follows that' in this direction also lies the continued prosperity of the stone business. As a compromise between the minute subdivisions devised by scientists and the extremely general and often erroneous clas sification of quarrymen, the following division may be adopted for quarrying operations: Limestones and Dolomites.— The sedi mentary and bedded rocks, composed essentially of lime carbonate, or the mixed carbonates of lime and magnesia, the latter receiving the specific title of dolomite. Such have been found to pass into each other by insensible gradations, certain quarries producing at the same time material which, if classed on purely chemical grounds, would be relegated to both divisions. Limestones may also carry a considerable per centage of quartz, when they are called silicious limestones. When clayey, they are called argil laceous limestones.

Marble.— Including stones identical in com position with those noted under limestones and dolomites, but which through crystallization and other changes, mainly physical, have come to possess properties rendering them desirable for high-grade building or ornamental work. The marbles of New York, recently brought to light by The Adirondack Lumber and Mineral Cor poration, for instance, are largely limestone, while those in Massachusetts, Berkshire County, are largely dolomite. With the marbles are also

included a small series of serpentine rocks, which are likewise utilized for decorative pur poses.

Sandstones and Quartzites.— Rocks com posed essentially of sands cemented together with silica or with silica and iron oxide, being made over, as it were, from the detritus of pre-existing rocks. Those classed as quartzites are sandstones which have been rendered more or less crystalline through the deposition of silica between the original sand particles, as in the case with the jasper of Sioux Falls, South Dakota, or the Potsdam sandstone of Saint Lawrence County, New York. The tuffs and other volcanic fragmental rocks and the blue stones are also here included.

Silica Sand.— Silica or silicious sand in cludes not only sand suitable for the manu facture of glass, but also a large quantity desig nated as engine and furnace sand. It exists in several States as a sandstone, requiring crushing and screening; as a stone that readily disintegrates when exposed to the action of the elements and needs only washing or burning to reduce the amount of organic matter and other impurities. On account of their use in industry as sand, they are discussed under that title.

Siliceous Crystalline Rocks.— Here are in cluded the true granites and syenites, together with trappean rocks, such as are often desig nated as black granites; the gneisses or so called striped or bastard granites; the mica schists; and melaphyre, basalt, andesite,. syenite, elatolite, diabase, gabbro, nonte, lispante, dio rite and other volcanic rocks.

Slate.— Induding argillaceous rocks, which, through the process of shearing and incidental chemical activity, have undergone a partial met amorphism, resulting in the development of a pronounced tendency to split along certain planes, which may or may not be parallel with the original bedding, into thin sheets suitable for roofing purposes. It is necessarily a conse quence that such are restricted to the regions of pronounced earth movements, such as have resulted in the formation of mountain ranges.

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