270 UNIVERSITY OP VIRGINIA PUBLICATIONS 



talline rocks of the Piedmont Plateau extends across the State in roughly a 

 general north-south line and in position nearly coincides with the meri- 

 dian 78°30'.* 



In the southern part of the State the Calvert formation is overlain by 

 the St. Mary's formation (middle Miocene), and along the western edge 

 the St. Mary's transgresses the Calvert and rests on the crystalline rocks of 

 the Piedmont Plateau. 



DISTRIBUTION AND OCCURRENCE OF THE SANDSTONE. 



In the Ashland area the sandstone does not outcrop in a continuous 

 bed. It was seen only in the form of irregular flat fragments lying loose 

 upon the surface. The fragments are of the same reddish-brown to yellow 

 color as the specimen submitted by Mr. Meyer. In size the fragments 

 range from those as large as a man's fist to some measuring 2 feet long, 2 

 feet broad, and 6 inches thick. There is as much variation in texture as in 

 size, and the rock accordingly ranges from a typical fine-grained sandstone 

 to a typical moderately coarse conglomerate, with intermediate gradations. 

 Much of it is very fine-grained, showing little visible quartz. Other pieces 

 are of varying degrees of coarseness, some containing quartz and quartzite 

 pebbles 2 inches in diameter. Some pieces show cross-bedded structure. 



The largest number of the sandstone fragments were seen on a small 

 mound 150 yards southwest of Mr. Sheldon's house, and scattered frag- 

 ments can be found both to the north and the south for a distance of half 

 a mile. On Mr. J. B. Davis's farm, which- adjoins the Sheldon farm on 

 the north, there are many pieces of the sandstone, though most of them are 

 smaller. However, many of the pieces, especially those found farther 

 north, are of lighter color and lower specific gravity than the fragments 

 from the Sheldon farm, though one of the richest specimens collected was 

 from the line between the Thomas Kies and John Boschen farms, half a 

 mile north of the Sheldon farm. The specific gravity is of value in field 

 examination, for specimens having low specific gravity show only a few 

 grains of zircon, whereas those having high specific gravity carry a large 

 percentage of the mineral. 



It is probable that the hard lumps of sandstone represent the local cemen- 

 tation of a sandy bed which, in most places, is soft or but slightly consoli- 

 dated, a characteristic of the Chesapeake group (Miocene). Partly or 

 wholly indurated sands, yielding somewhat highly ferruginous crusts and 



* See the geological map of Virginia, Virginia Geological Survey, Charlottesville, 

 1911. 



