Page:Encyclopædia Britannica, Ninth Edition, v. 24.djvu/281

Rh north and west ; and it has accordingly as nearly a climate of means as any of the Atlantic-bordering States can have. Its position and physical structure also give great variety to its climate : that of its bordering sea islands and large peninsulas is insular ; that of its great Tidewater and Midland plains is warm temperate ; that of Piedmont and the Great Valley is typically mild temperate; and that of the Blue Ridge plateau and of the high valleys and table lands of Appalachia is more uniformly cool temperate than in higher latitudes. Its climatic range, in the average latitude of 38 N., is from the sea-coast to 500 miles inland, and from the sea-level to 5700 feet, a range that is equivalent to 19 of latitude, and that gives to Virginia all the adaptations for production embraced between 36 30 and 59 N. lat. This wide range finds expression in the market-gardens and temperate fruits and trees and the extensive sweet potato, cotton, and peanut fields of Tidewater ; in the large plantations of tobacco, hard-grained winter wheat, and the dented- seed (the large variety) Indian corn, and in great forests of pitch- pines, oaks, &c., in Midland and Piedmont, and in the lower portions of the Valley and Appalachia ; in the productive vineyards and orchards of Piedmont and the adjacent slopes of the Blue Ridge ; in the perennial pasture-lands the native homes of the rich blue grass of the higher levels of Piedmont, of the crests and plateaus of the eastern Blue Ridge, of the Great Valley, and of the extensive limestone valleys and ridges of Appalachia ; in the large cereal crops and dairy products of the Valley ; in the big cattle farms and ranges of Appalachia, the Blue Ridge, and the more elevated parts of the Valley ; in the flax, buckwheat, Irish potato, cabbage, and other north-country crops that flourish in the Blue Ridge, the higher parts of the Valley, and Appalachia ; and in the north-land balsams and other cold climate trees and vegetation that clothe the higher levels of the Blue Ridge and of Appalachia.

The mean annual temperature zones of Virginia are 60 to 65 in eastern Tidewater ; 55 to 60 in western Tidewater, and most of Midland ; 50 to 55 in the higher parts of Midland, in most of Piedmont, and in the lower parts of the Valley and Appalachia ; 45 to 50 in north-east Piedmont, in most of the Valley, and in the lower valleys of Appalachia ; and 40 to 45 on the Blue Ridge, on and near the high levels of the Valley, and in most of Appa lachia. The average for the State is near 56, ranging from 48 in the highlands to 64 in the lowlands from the mean adapted to grass to that suitable for cotton. The changes of temperature are great, but not so sudden or so extreme as they are in the regions to the north-east and north-west.

The prevailing winds are from the south quadrants, generally shifting between south and west ; next in frequency are those be tween north and west ; high winds are rare, except along the coast. The rainfall is abundant and well distributed throughout the seasons in every part, there being two sources of supply, one from the Gulf by the south-west and one from the Atlantic by the south-east winds ; the average annual precipitation is from 32 to 44 inches, except in a belt extending north-west from the mouth of Chesapeake Bay towards Staunton, in which it is from 44 to 56 inches ; there is a gradual decrease in the rainfall from the coast westward. The snowfall is generally light, some winters insignificant ; and the snow soon melts, save in the elevated regions.

Virginia is noted for the clearness of its skies, the purity of its air, and its freedom from great storms. Its climate is moist without being damp, and so mild as to invite to living much in the open air ; its winters are short, its periods of seedtime and harvest long ; and its healthfulness is attested by the vigour and longevity of its people.

Geology. The subjoined table of the geological formations found Geology Pennsylvania and New York, in Virginia, correlated with those of and with the general groups and systems of the American geological scale, follows, in the main, the late Prof. William B. Rogers :

Systems. &amp;gt; Cainozoic. 196. Subdivisions or Formations in Virginia. General Groups. Quaternary Quaternary. Pliocene (Upper Tertiary). Miocene (Middle Tertiary) i- Tertiary Pliocene (Upper Tertiary) ) Miocene (Middle Tertiary) ^ Eocene (Lower Tertiary) ) lesozoic. &amp;gt; Carboniferous. IS and 17. Jurasso-Cretaceous (Upper Mesozoie) ( 17 and 1C. Jurasso-Triassic (Lower Mesozoic) j 146(xiii.). Middle Coal group UpperCar- ^ 14rt(xii.). Lower Coal group /boniferous. 1 I 136 (xi.). Greenbrier shales and lime- Middle Car- stones (Carb. limestone). / boniferous. 13a (x.). Montgomery grits and coal- Lower Car- I measures (Vespertine)... /boniferous. ) 12 (ix.). Catskill red sandstone (Upper Devonian) -v 116anda/Chemung and Portage shales (Middle I (viii.). Devonian) J-Devonian. 10c, b, & j Genesee, Hamilton, and Marcellus slates, I a (viii.). | .fee. (Lower Devonian) 8 (vii.). Oriskany sandstone Lower Helderberg limestones Silurian (Upper Mesozoic. 7 (vi.). 06 (v.). 5a (iv.). 4c and 6 / Hudso (Hi.). slate 4a (Hi.). Trenton and Great Valley f Clinton shales and sand rocks.. Medina and Oneida sand rocks. River und Utica &quot;1 Upper Cambrian, limestones., Silurian). Cambrian (Lower Silurian). Palaeozoic. j&quot; Primal. . it ), Valley dolomites, &amp;lt;fcc.) ... ( 2 (i.). Potsdam sandstones.shales, ( Cambrian frc / 1. Archaean (Huronian, Laurentian, &c., Primary)

Note. The first or Arabic numbers and the letters of the above are the numberings of the formations and their subdivisions now generally recognized and used in North America; the Roman numbers in brackets are the equivalent formations as numbered and used by the Rogers Brothers in the Pennsylvania and Virginia reports.

As the accompanying geological map shows, Midland, Piedmont, and the Blue Ridge grand divisions, over 20,000 square miles, or about half the land area of the State, are underlain by the Archaean or old Primary and metamorphic rocks ; within this Archaean area are a dozen or more patches, large and small, of the Jura-Trias (forma tions 16, 17, and 18) or Mesozoic rocks, some of them with valuable coal-beds, that in later times were deposited in depressions, lake-like basins, in the Archaean rocks. The Cambrian (Lower Silurian) areas, the Virginia formations i., ii., and iii., include all the Great Valley (limestone) and numerous limestone valleys of Appalachia, some of them, like that of Clinch river, quite large in all some 10,000 square miles of surface having within them detached mountain ranges of more recent forma tions. The Silurian (Upper Silurian) areas, those where the Virginia formations iv. , outcrop, are mountain ranges, detached once in the Great Valley, and ranges and chains of them in Appalachia, for these formations, made up largely of massive sand-rocks, are mountain-builders. The Devo nian areas, Virginia formations viii. and ix., are principally those of the slaty or &quot;poor&quot; valleys of Appalachia, No. viii. being a formation from which stream-valleys are liberally carved, though ix., chiefly sand-rocks, often holds it up to included or bordering ridges. The Lower and the Middle Carboniferous rocks, Virginia formations x. and xi., outcrop in long and narrow belts or strips of Greenbrier shales and limestones (xi. ), and adjacent narrow and long mountain ranges of Montgomery grits and coal-measures (x.), in south-west portions of the Valley and of Appalachia, and in small mountain areas elsewhere in Appalachia. The Upper Car boniferous, Virginia formations xii. and xiii. , the Lower (xii.) and the Middle (xiii.) Coal groups, underlie all the thousand square miles of Trans-Appalachia, where the semi-bituminous coking coals of the Lower Coal group are exposed, above water-level, in their best conditions of purity (high in carbon, low in volatile matter,

1 Formations xiv., xv., and xvi., the Upper Coal group, are not known in the present limits of Virginia.

EB9 Virginia - geological map.jpg