The largest features of the drainage system are the tidal estuaries which have invaded the coastal plain as far as the °fall linep belt, dividing it into peninsulas long and narrow in outline. The greatest of these estuaries is, of course, Chesapeake Bay, to which the estuaries of the Potomac, the Rappahannocic and the James — from 150 to 200 miles long—and the smaller ones of the York. the Wicomico, the Piankatank and the Nansemond rivers and of Mobjack Bay and many of lesser tide pay their constant tribute. The rivers of the coastal plain are tidal with low velocities and art navigable as far inland a.s the Piedmont border — the so-called gall line belt.) Climate.— Virginia lies within the temperate zone and, speaking broadly, there are no great extremes of heat and cold. The tetnperature is quite stable from day to day in the coastal plain. The mean temperature is; Winter 39.8°, spring 56.8°, summer 77.2°, autumn 60.8°. The average ntunber of days each year with a maximum temperature above 90° is 28; below 32°, 55. Greater ranges in the monthly and sea sonal mean occur in the elevated area known as the Piedmont province. Marked c.hanges occur suddenly, but not frequently ,in winter. Mean temperature: Winter 35.8°, spring 553°, sum mer 75°, autumn 57.4'; annual 55.9% average number of days each year with maximum tem perature above 90', 25; below 32°, 72. In the Great Valley province the valleys become filled with heated air in the day and at night cool currents flow down the mountains into the val leys. For this reason the greatest differences in mean daily and monthly temperatures occur here. Mean temperature : Winter 33.8°, spring 52.7°, sununer 71.3°, autumn 55.1°, annual 532°; average ntunber of days each year with minimum temperature above 90°, 13; below 32°, 98. The average annual precipitation in the coastal plain province is 46.61 inches; the Pied mont 42.50 and the Great Valley 43. The pre vailing direction of the wind is northeast in the coastal plain ; northwest in the Piedmont plateau .and west in the Great Valley; mean annual velocity for the State 6.3.
The coastal plain is composed of sediments, mostly sands, clays and marls, rang ing in age from lower cretaceous to quarter nary. The beds strike in general from north to south with a low easterly dip. The Pied mont piateau is formed of a mixture of highly metamorphosed sedimentary and igneous rocks of prepaleozoic and early paleozoic age, with exposures of fresh rock less numerous than farther north. The rocks are crystalline with gneisses and schists. The abundance and excellence of the granite make them important in commercial work. There are areas of triassic sediments and over parts of the south central portion of this province are found voleano-sedimentary rocks. The Blue Ridge is composed of pre-Cambrian igneous rocks with Cambrian sandstones and slates on the north west and on the southeast, in places, by silicious sediments of the same age. The Valley of Virginia and the Alleghany ridges are com posed of paleozoic sedimentary rodcs ranging in age from Cambrian to carboniferous.
Minerals.— Coal is by far the largest min eral interest of the State. The annual output has been about 8,000,000 short tons, of which more than nine-tenths was bituminous, and its value at the mines has been somewhat in ex cess of $8,000,000. In 1916 the output was
9,707,474 short tons, valued at $10,261,424. Prac tically all of it was mined in the mountains c f southwest Virginia, in the counties of Wise, Tazewell, Montgomery, Lee, Russell and Pulaski, although there is coal elsewhere. Iron is mined in the Valley and Piedmont provinces of the west and southwest_ At Crimora, in the Valley of Virginia, more manganese has been taken Chan from any other mine in the United States. In 1916 the output of manganese and carboniferous iron ores was 40,117 long tons, valued at $'217,136. Other mineral productions for the year 1916 were: Coke 1,242,332 short tons, value $1,695,361; clay products, including brick and tile clay mined and sold and pottery, $1,695,151; fimestone $1,087,247; iron ores 486,798 long tons, $1,000,118; soapstone and talc 28,355 short tons, $564,228; granite $451,697; mineral waters 2,313,616 gallons, $248,906; slate 36,007 squares, $165,483; sand stone $66,217.
Natural The best known and perhaps the most visited of the natural attrac tions of the State is tlie Natural Bridge, 14 miles from Lcxington in the county (Rock bridge) named for it. This great bridge, in the' formation of which human agency had no part, is 2151/2 feet high, measuring from the top of the span to the creek which flows under it. In the same county, 12 miles southeast of the Warm Springs, is the °Blowing Cave,* which emits a constant current of air which is strongest in dry, frosty weather and weakest in long periods of rain. °Regular inspirations and expirations of air by caverns and fissures have been probably enough accounted for by supposing them combined with intermitting fountains, as they tnust, of course, inhale air while their reservoirs are emptying themselves and again emit it while they are filling, but a constant issue of air only varying in its force as the weather is dryer or damper will require a new hypothesis.) Sixteen miles northeast of the Warm Springs, in Bath County, is a spring whose waters ebb and flow. At intervals, in the dryest weather of summer, the water flows cut as if suddenly released from a dam, and continues at flood 10 or 12 hours, and then gradually declines. In the same ldnd of weather the periods of flow will vary from two to three days and sometimes occur' daily. There are numerous caves. The most noted are Weyer's in Augusta County and the Luray caverns in Page. Crabtree Falls, near the sum mit of the 13lue Ridge mountains, in Nelson County, consist of three descents, the longest leap being 500 feet. Balcony Falls, at the meeting of Rockbridge, Amherst and Bedford counties, where the James makes its way through the Blue Ridge, is a scene but little inferior to the spectacle of the passage of the Potomac through the same mountains at Harper's Ferry. Mountain Lake, in Giles County, 3,500 feet above the sea, is the antithesis of Lake Drum mond in the Dismal Swamp. Scott County furnishes a Natural Tunnel by which buffalo made their way through the mountain. The use of it by the Virginia and Southwestern Railroad illustrates the change which has taken place since the days of Daniel Boone.