362 Campbell — Rogers } s Geology of the Virginias. 



west." (pp. 288-290). " Eocks of this description occupy a 

 large portion of the district (northern). Besides being met with 

 in intermediate lines, the}?- are largely developed in two exten- 

 sive tracts, one of which stretches in the form of a belt from 

 the eastern flank of the Blue Ridge, to the neighborhood of 

 Southwest Mountain in Albemarle county, gradually contract- 

 ing in width in its prolongation toward the northeast, and 

 finally near the Potomac, compressed between the flank of 

 Short, Hill and a line some distance west of the Kittoctin 

 Mountains ; the other forming an irregular triangular area, hav- 

 ing its apex a little west of Fredericksburg, its eastern side in 

 nearly a meridional direction, coinciding with the eastern limit 

 of primary rocks along the head of tide, and its western side 

 parallel to the general course of Southwest Mountain, and termi- 

 nating a few miles west of Columbia. . . . Along the eastern 

 margin and for some miles westward, the variety chiefly met 

 with is a gray rock, consisting of quartz, feldspar and black 

 mica with occasional spangles of white mica, and scattered 

 grains of hornblende. It is of an even texture, readily separ- 

 ating into large slabs and blocks, suitable for columns and other 

 purposes. ... Of this variety innumerable exposures are pre- 

 sented on both sides of the James river in and above Richmond, 

 and on the Appomattox in and above Petersburg, and a simi- 

 lar rock, though in much less extent, is seen on the Rappahan- 

 nock above Fredericksburg." (pp. 455-456). 



" Micaceous, Talcose and Argillaceous /Slates (lb). — Westward 

 of the triangular district of gneiss rocks just alluded to we 

 find a broad belt of more slaty rocks, which, according to the 

 peculiar ingredient predominant for the time, are either of the 

 micaceous, talcose or argillaceous character. This belt reaches 

 nearly to the eastern flank of Southwest Mountain, in Fluvanna, 

 Albemarle and Orange counties ; and farther north, though in 

 part covered by the middle secondary rocks (Mesozoic), there 

 widely expanded over the corresponding region, is still trace- 

 able in considerable width east of that formation through Fau- 

 quier, Prince William and Fairfax counties, as well as in 

 narrow and interrupted tracts along the base of Bull Run and 

 Kittoctin Mountains. . . . 



" Referring however merely to general features, the mica- 

 ceous composition, thus most strikingly exhibited toward the 

 eastern margin of the slaty belt, is seen changing as we pro- 

 ceed west into one in which talc is more or less blended with 

 the mica, and even in some places entirely displaces it. . . . 



" Throughout the whole of this belt of slaty rocks, veins and 

 beds of quartz are of very common occurrence, and, in the 

 talcose and micaceous slates especially, are frequently more or 

 less auriferous. In fact this belt includes nearly every locality 



