_Granite_, including certain other closely related rocks, is one of the oldest and most useful building stones. The New England States are the greatest producers, while the Piedmont Plateau district (east of the Appalachians) from Philadelphia to Alabama also contains important granite quarries. In the Adirondack Mountains, in Wisconsin and Minnesota, through the Rocky Mountains, and the Sierra Nevada Mountains there are extensive areas of granite which are relatively little quarried. The granite occurs only in regions of highly disturbed rocks, usually in mountains or hills, where great volumes of the molten rock were forced into the earth's crust, cooled, and later laid bare by erosion. _Marble_, according to geological definition, is a metamorphosed limestone, that is a limestone which has been crystallized under conditions of heat, pressure, and moisture within the earth. More loosely in trade any limestone which takes a polish may be called marble. The greatest marble-producing districts of the United States are western New England (especially Vermont) and the Piedmont Plateau and Appalachian Mountains in rocks of Paleozoic age. In northern New York and the mountains of the west there are relatively few marble quarries. Ordinary _limestones_ are widely distributed in many States where they range in age from early Paleozoic to Tertiary. Most of the quarries supply stone for near-by markets. The so-called Bedford limestone of Indiana has, for many years, been perhaps the most widely used limestone for building purposes in the United States. _Sandstones_, which are stratified rocks consisting mainly of rounded quartz grains cemented together, are widely used in building operations. Like limestones, they are very widespread in formations of all ages except the very old. There are many sandstone quarries supplying more or less local markets throughout the country. Two of the best known and most widely used sandstones are the so-called brown-stone of Triassic Age extending interruptedly from the Connecticut Valley of Massachusetts to North Carolina, and the Berea, Ohio, sandstone of light gray color and uniform texture. _Slate_ is mostly a metamorphosed shale, that is a shale which has been subjected to great pressure within the earth so that the stratification has been obliterated and a well defined cleavage has been developed at right angles to the direction of application of the pressure. Good slate is fine-grained, dense, and splits readily into wide thin plates. It occurs only where mountain making pressure and metamorphism have been brought to bear upon the strata. Most of our great slate quarries are located in early Paleozoic rocks from New England through the Piedmont Plateau. Some quarries are also located in Arkansas, Minnesota, and westward to California.