GEOLOGY AND 'MINERAL RESOURCES. As in the other Atlantic States, the prineipal geological formations run in parallel bands from southwest t-o northeast, and correspond closely to the topographical regions, whose characteristics, in fact, are dependent upon the underlying rock formations. The coastal plain or tidewater sec tion is overlaid by unconsolidated strata of sand, gravel, clay, and marl of Tertiary and later origin. The western boundary of the coastal plain formation runs from the neighborhood of Washington due south, passing west of Richmond. Between this line and the Mile Ridge the country is of -1relnran origin, consisting of granite, gneiss, syenites, and slates, with intrusions of green stone in the west. The central part of the region, however, was submerged in early Mesozoic times, and several large patches of rock belong ing to the Jura-Trias system still remain. The Blue Ridge consists mainly of Potsdam sand stone of the Cambrian system, and the valleys and ridges to the west of it are of Lower Pale ozoic age, Silurian limestone predominating in the valleys, and Devonian rocks on the ridges. A peculiar feature of the limestone region in the Great Valley is the formation of great cav erns which rank among the foremost natural curiosities in the country, such as \Veyer's Cave in Augusta County, and the arched remnant of a cave, famous as the 'Natural Bridge,' in Hock bridge County.
Virginia has a great and varied mineral wealth. Iron is found as magnetite along the eastern use of the Blue Ridge, limonite On its western slope and in various other localities, and red Immo tite in the western iNlieghanies. Other metals found in the mountain region are zinc, lead, tin, and copper, and manganese is widely distributed. Through the Arelnean rocks of middle Virginia runs an auriferous quartz reef, and silver is also found in small quantities. Building stones, granite, limestones, and sand stones are found of great beauty and variety, and in inexhaustible quantities. Hydraulic limestone is also abundant, and in the southwestern cor ner of the State there are immense ledges of gypsum and rock salt. Even the tidewater section contains valuable minerals in the form of greensand marl.