Some of the softer limestones possess qualities which specially commend them for building materials. For example, the cream colored limestone of the Paris basin (calcaire grossier) which is so soft when first quarried that it may be dressed with great facility, hardens on exposure, and is a durable stone. Walls laid up of this material are frequently planed down to a common surface, and elaborately ornamented at small expense. The Topeka stone, found and now largely used in Kansas, has the same qualities. It may be sawed out in blocks almost as easily as wood, and yet is handsome and durable when placed in position. The Bermuda stone and coquina are treated in the same way.
Large quantities of limestones and dolomites are quarried in nearly all of the Western States. These are mostly of a dull grayish color, and their uses are chiefly local. The light colored oolitic limestone of Bedford, Indiana, is, however, an exception to this rule. Not only are the lasting qualities fair and the color pleasing, but its fine even grain and softness render it admirably adapted for carved work. It has been very widely used within the last few years. This stone is often found in layers 20 and 30 feet thick, and is much used for bridge piers and other massive work.
Sandstones. "Sandstones vary much in color and fitness for architectural purposes, but they include some of the most beautiful, durable, and highly valued materials used in construction. What ever their differences, they have this in common, that they are chiefly composed of sand—that is, grains of quartz—to a greater or less degree cemented and consolidated. They also frequently contain other ingredients, as lime, iron, alumina, manganese, etc., by which the color and texture are modified. Where a sandstone is composed exclusively of grains of quartz without foreign matter, it may be snow-white in color. Examples of this variety are known in many localities. They are rarely used for building, though they may be em ployed for that purpose with excellent effect. They have been more generally valued as furnishing material for the manufacture of glass. The color of sandstones is frequently bright and handsome, and constitutes one of the many qualities which have rendered them so popular. It is usually caused by iron; when gray, blue, or green, by the protoxide, as carbonate or silicate; when brown, by the hydrated oxide; when red, by the anhydrous oxide. The • purple sandstones usually derive this shade of color from a small quantity of manganese.
"The texture of sandstones varies with the coarseness of the sand of which they are composed, and the degree to which it is con solidated. Usually the material which unites the grains of sand
is silica; and this is the best of all cements. This silica has been deposited from solution, and sometimes fills all the interstices be tween the grains. If the process of consolidation has been carried far enough, or the quartz grains have been cemented by fusion, the sandstone is converted into quartzite,—one of the strongest and most durable of rocks, but, in the ratio of its compactness, difficult to work. Lime and iron often act as cements in sandstones, but both are more soluble and less strong than silica. Hence the finest and most indestructible sandstones are such as consist exclusively of grains of quartz united by siliceous cement. In some sandstones part of the grains are fragments of feldspar, and these, being liable to decomposition, are elements of weakness in the stone. The very fine grained sandstones often contain a large amount of clay, and thus, though very handsome, are generally less strong than those which are more purely siliceous.
"The durability of sandstones varies with both their physical and chemical composition. Sandstones composed of nearly pure silica which is well cemented are as resistant to weather as granite, and are very much less affected by the action of fire. Taken as a whole, they may be regarded as among the most durable of building materials. When first taken from the quarry and saturated with quarry wat.r, they are frequently very soft, but on exposure become much harder by the precipitation of the soluble silica contained in them.
." Since they form an important part of all the groups of sediment ary rocks, sandstones are abundant in nearly all countries; and as they are quarried with great ease, and are wrought with the hammer and chisel with much greater facility than limestones, granites, and most other kinds of rocks, these qualities, joined to their various and pleasing colors and their durability, have made them the most popular and useful of building stones." The United States is abundantly supplied with sandstones suitable for building purposes. The following are some of the most noted: 1. The Brownstones of Connecticut and New Jersey were formerly much used in buildings, particularly of the Atlantic cities; but experience has shown that they are seriously lacking in durability, since their cementing material is readily decomposed by the acids in the atmosphere of cities.