LIMESTONE, a common and widely dis tributed rock, consisting essentially of car bonate of lime and varying greatly in com position, color and texture. Most limestones are of organic origin and represent the calcare ous remains of sea animals, such as corals, foraminifera and mollusks. These remains may be reduced to a fine ooze by the action of the waves and in other ways, and the rock resulting from the consolidation of this ooze may show no trace of organic origin. Some limestones have been formed by the precipita tion of calcium carbonate from sea water through evaporation in confined estuaries. Other limestones (travertine, calcareous tufa) have been formed by the deposition of calcium carbonate from springs, while still others repre sent calcareous deposits in fresh-water lakes. The varieties of limestone are almost endless, including the crystalline limestones or marbles. Thus starting with nearly pure calcium car bonate, the calcium may be replaced gradually by magnesium till finally we have dolomite, the double carbonate of calcium and magnesium. Magnesian limestone is the proper designation until the ratio of calcium carbonate to mag nesium carbonate becomes 100 to 84, beyond which it is dolomite. Pure dolomite contains 21.72 per cent of magnesia, hut limestones con taining over 5 per cent are said to ,be dolomitic. Again the lime may be replaced by silica, with a gradual transition from limestone through eherty limestone to pure cherts; or again iron oxide may replace lime with a resulting transi tion from limestone to merchantable iron ore. Besides these chemical transitions silicious or argillaceous sediments may be laid down with the calcareous material, and in the resulting rocks we may trace gradual changes from limestone through limy sandstones to pure sandstone and from limestone through marls or calcareous shales to ordinary shales. Bitu minous matter may make limestone black or give rise to asphaltic varieties. Besides all these varieties of composition, limestones are often classified according to their texture, as earthy limestone, oolithic limestone with a con cretionary texture, like the roe of fish, etc. Under rock stresses, with possible rise in tem perature, limestone becomes recrystallized and is then known as marble. Chalk is a soft and powdery textured limestone. Limestones are also classified according to the uses to which they are put, and thus we have cement rock or hydraulic limestone used for making cement, lithographic limestone, st"uary marble, etc.
The various limestones and marbles are widely used for building purposes, and a great amount of limestone is annually burnt to lime or to cement, though no statistics of the amount thus used are available (see CEMENT; LIME). Limestone is also used as a flux in smelting iron and other ores, the total amount thus used in the United States in 1902 amounting to fully 9,000,000 tons. Of the limestones used as build
ing stone, particular mention may be made of the bluff or blue °Eolithic Bedford limestone of Indiana and of the marbles of Vermont, Georgia and Tennessee. Marble or limestone is also used as a source of carbonic acid gas for aerated waters.
The uncertainty of composition of a lime stone deposit is a constant difficulty in utilizing it for cement and flux. It is a matter of com mon experience among quarrymen that to obtain uniform stone they must follow the beds of desirable composition, rather than to cut in straight lines. Limestone is found in horizon tal deposits in successive layers, on what was once a sea bottom, and it varies in composition with depth. That which was laid at one period is most likely to be uniform, and this means quarrying along the strata selected, and also following what was formerly the shore line, if this can be determined.
Limestone is one of the most common rocks, and is found in almost every State and Terri tory of the United States. Being heavy for its value, it does not pay to freight it great distances, hence efforts are made to quarry it in various localities for nearby consumption. About 15 per cent of the area east of the Rockies bears limestone. Most of the New England limestone occurs in the form of mar ble, but deposits suitable for lime are found in large quantities in Berkshire County, Mass., and Litchfield and Fairfield counties, Conn. New York and Pennsylvania are both rich in limestone beds. There are extensive quarries near Buffalo that supply the blast furnaces. The Lehigh district of Pennsylvania contains immense quantities of cement rock and purer limestone beds. The valley of Virginia con tains great deposits suitable for lime-burning, and easily accessible. This limestone belt ex tends across the corner of West Virginia, through Maryland into Pennsylvania. Calcare ous rocks predominate in Tennessee, northern Alabama and northern Georgia. The greater i part of the lime made in Wisconsin is burned from Silurian magnesian limestone found in the eastern part of the State. An extension of this belt of rock runs into Michigan. In In diana the Bedford limestone, which is light gray, has attained a reputation as a building stone. Limestone is quarried in the southern part of Mississippi, and at intervals all the length of the Mississippi River. There is also a wide distribution in Missouri and Kansas, as well as Texas, Utah, Washington, Wisconsin, etc.
The total value of the limestone produced in the United States in 1909 was fully $32,000, 000. See CALC-TUFA ; CALCITE; CHALK; CORAL; DOLOMITE; MARBLE and MARI..