268 UNIVERSITY OF VIRGINIA PUBLICATIONS 



in Hanover and Goochland counties, and under a hand lens no difference 

 in appearance could be distinguished. As the rutile of these counties 

 occurs with a very black ilmenite, it was thought that the specimen might 

 possibly be a fine-grained mass of titanium minerals. Microscopic exami- 

 nation of a thin section, however, showed the rock to be a sandstone com- 

 posed of very small grains of ilmenite and zircon (zirconium silicate, ZrSi04), 

 together with a few grains of other minerals, chiefly quartz and silicates, 

 cemented with limonite. 



In June, 1911, the writers, in company with Mr. Meyer, visited the 

 locality from which the latter obtained the original specimen, on the farm 

 of Mr. F. B. Sheldon, 3 miles west of Ashland, Hanover Count j^, and about 

 20 miles north of Richmond. 



GENERAL GEOLOGY OF THE AREA. 



The area of zirconiferous sandstone forms a part of the western edge of 

 the Coastal Plain, near and along the overlap of the sediments upon the 

 older crystalline rocks of the Piedmont Plateau (see map, fig. 1). Along 

 this edge (the "fall-line") the surface is somewhat roughened from erosion, 

 but to the east it becomes more gently rolling and is essentiall}^ flat and 

 featureless. The area lies on the south side of South Anna River, but 

 within its drainage basin and only a short distance southwest of its conflu- 

 ence with the North Anna to form Pamunkey River. 



The sandstone outcrops along a low ridge having gently sloping sides 

 and a general direction of N.20°E. At the point where the sandstone 

 seems to be most abundant and perhaps richest in zircon the ridge marks 

 the western edge of the Calvert formation, the lowest formation of the Chesa- 

 peake group (Miocene). Within this area and for some distance north 

 and as far south as a point 25 miles north of Petersburg the Calvert for- 

 mation transgresses the underlying older Coastal Plain sedimentary 

 formations, and its western margin rests upon the crystalline rocks of the 

 Piedmont Plateau.* The Calvert formation in Virginia is about 200 feet 

 thick and consists chiefly of sands, clays, marls, and diatomaceous earth, 

 fine-grained sands being predominant. Diatomaceous earth has not been 

 identified in the Ashland area. 



Extending westward from the foot of the west slope of the low ridge 

 mentioned above are the crystalline rocks of the Piedmont Plateau, chiefly 

 granites and gneisses, most of which are of pre-Cambrian age. The con- 

 tact between the sedimentary formations of the Coastal Plain and the crys- 



* Virginia Geol. Survey, Bull. No. IV, 1912, p. 126 et seq. 



