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SANDSTONE. Sandstones are rocks made up of grains of sand which are cemented together by siliceous, ferruginous, calca reous, or argillaceous material. In most cases the cementing ma terial determines the color, the various shades of red and yellow being due to iron oxide, the purple tints to oxide of manganese, the gray and blue tints to iron in the form of ferrous oxide or carbonate. The texture of the stone varies according to the sizes of the sand grains, of which there are all gradations from those that are so fine as to be barely discernible to those that are very coarse. The hardness, strength, and durability of the stone is dependent upon the character of the cementing material. Only the harder and tougher sandstones, generally those in which the cementing ma is siliceous, are used for paving. Sandstone paving blocks are common in the Lake and Western cities. The principal quar ries from which sandstone paving blocks are obtained will be briefly described.

Medina Sandstone.

This stone is found in the state of New York, extending from Oneida and Oswego counties on the east along the shores of Lake Ontario westerly to the Niagara river. It continues into Canada, and is found also to some extent in Pennsylvania and Virginia. It is generally a deep brownish red in color, though sometimes light and yellowish, and in a few localities gray. The coloring matter is oxide of iron. It is both fine grained and coarse grained in texture, the latter being of a deeper color as the iron cement more easily penetrates the inter stices between the larger grains. The principal mineral constituent is quartz associated with some kaolinized feldspar. The cementing material is mainly oxide of iron with some carbonate of lime. The stone is evenly bedded, and the beds are divided into blocks by systems of vertical joints, generally at right angles to each other, an arrangement which greatly facilitates the work of quarrying. It has a specific gravity of about 2.60, and consequently it weighs about 148 pounds per cubic foot. It absorbs 2f to 31 per cent of water, but it is not materially affected by alternate freezing and thawing.

This stone is much used for paving in the Lake cities, where it is often preferred to granite since it does not wear slippery.

Potsdam Sandstone.

This formation is worked at a number of places in the state of New York, but the largest quarries are near Potsdam. In general the stone is grayish, yellow, brown, and sometimes red in color, according to the amount and kind of iron in composition; and it varies in texture from a strong compact quartzite to a loosely coherent granular mass. That quarried at Potsdam is hard and compact, evenly grained, and reddish in color. It is largely used as a building stone and to a considerable extent also for pavements. It consists almost entirely of quirtz and the cementing material is almost wholly silica.

Colorado Sandstone.

In Boulder County, Colorado, are several deposits of sandstone that furnish stone for building and also for paving purposes. The stone varies in color from gray to a light red according to the composition of the iron compounds. It is found in layers varying from * inch to several feet in thickness, splits easily, and breaks readily at right angles, so that it is formed into flagging, curb stones, and paving blocks without difficulty. It is hard and tough, and wears well in a pavement. Its grain and texture are such that, although it wears smooth, it is never slip pery; and after a little wear it forms a smooth and pleasing pave ment, very similar to one made of Medina stone.

Sioux Falls Quartzite.

This is a metamorphic sandstone gnu-lied at Sioux Falls, South Dakota. The stone is almost .pure silica with only enough iron oxide to give it color, which varies from light pink to jasper red. It is very close grained, and will take a polish almost like glass. It is said to be the hardest stone in this country. Its crushing strength is about 25,000 pounds per square inch. It possesses a remarkably good rift and grain, although not as perfect as that of granite. It is used considerably as a paving material, being shipped as far east as Chicago; but it wears smooth with a glassy surface.

Kettle River Sandstone.

This is a fine-grained, light pink sandstone, found in large quantities at Sandstone, Minn., about a hundred miles north of Minneapolis, which has been used for paving purposes in Wisconsin and Minnesota. The stone wears flat, does not polish, and approaches granite in its resist ance to crushing.