. Bulletin of the Philosophical Society. Philosophical Society (University of Virginia). Scientific Section; Science; Philosophy. 276 UNIVERSITY OF VIRGINIA PUBLICATIONS Zircon is an almost constant minor accessory mineral in the crystalline rocks, especially granites and gneisses, of this old shore and its extension westward, and in places it occurs in large masses. Thin sections of granites occurring immediately west of Ashland and at other places in the Piedmont Plateau of Virginia show the presence of zircon, chiefly as inclusions in the quartz and feldspar. Near Goulden post-office, 10 to
. Bulletin of the Philosophical Society. Philosophical Society (University of Virginia). Scientific Section; Science; Philosophy. 276 UNIVERSITY OF VIRGINIA PUBLICATIONS Zircon is an almost constant minor accessory mineral in the crystalline rocks, especially granites and gneisses, of this old shore and its extension westward, and in places it occurs in large masses. Thin sections of granites occurring immediately west of Ashland and at other places in the Piedmont Plateau of Virginia show the presence of zircon, chiefly as inclusions in the quartz and feldspar. Near Goulden post-office, 10 to 15 miles southwest of the Ashland area, pieces of zircon 3 inches in diameter weathered out of pegmatite dikes have been noted on the surface. Massive zircon •v\athout crystal outline, measuring 4 by 6 inches, has been observed in the pegmatites of Amelia County, Virginia. Similar dikes occur in the gneiss-granite complex of the Piedmont Plateau, forming the old shore-line which extends entirely across Virginia from Maryland into North Carolina, roughly coin- ciding with the meridian of 77° 30". The zircon in the sandstone was not derived, however, from the pegmatites in which it occurs in comparatively large masses, but from the granites and gneisses which carry it in innumer- bearin^ sa/idstoi. ^ FVe-Cambrian Arani"has andineJsses* * / ' ' Fig. 2. GeneraliziED East-West Section Across the Fall-Line near Ash- land, Virginia. Illustrating the occurrence of zircon-bearing sandstone. able very small crystals. It seems probable that similar zircon-rich sand- stones may occur at numerous points along this old shore-line. Many zir- con-bearing deposits may be covered bj' later sediments and some may have been removed by erosion, but it is probable that others, which may be richer or poorer, will be discovered along the contact of the granite and gneiss of the Piedmont Plateau with the overlying sediments of the Coastal Plain. It is probable that some magnetite was pres
Size: 3614px × 692px
Photo credit: © Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookd, booksubjectphilosophy, booksubjectscience
