STRUCTURAL FEATURES. 179 



was continuous, with some interruptions, up to the close of the Car- 

 boniferous era. 



The age of the last disturbance in the region under consideration 

 cannot be fixed definitely in geologic time. That it occurred after the 

 deposition of the Carboniferous limestone is certain, for in the regions 

 immediately adjacent this formation is involved in the folding of Brushy 

 mountain. The evidence for fixing the limit in the other direction is 

 not so good, and we cannot positively say whether it occurred before the 

 great Carboniferous conglomerate was laid down in the coal basin to the 

 northwest or \vhether it was folded after all the Carboniferous sediments 

 were deposited. The available evidence is negative, but indicates that 

 the region of the Great valley southeast of the coal field along the New 

 river was above sealevel when the coal was forming in the basin to the 

 northwest, and if this is correct the folding in the valley region probably 

 antedated it. 



The most prominent structural feature due to this latest period of dis- 

 turbance is the Walker mountain fault, shown on the map at A-B. 

 Northwest of this fault the structure is quite regular and all the forma- 

 tions appear to be present in their regular order of sequence. South of 

 the fault the condition of the formations is quite different and, as they 

 bear no ver}'' close structural relation, will be described in detail. 



Price Mountain : General Description. — Northwest of Christiansburg 

 and north of the line of the railroad lies Price mountain, a low ridge not 

 more than 800 feet above the general lev^el of tlie surrounding country, 

 and between three and four miles long. The region surrounding this 

 small mountain mass is composed of tlie Shenandoah limestone, and in 

 structure bears no relation to the structure of the mountain. The latter 

 is an anticline, the core of which is composed of the sandstones, shales and 

 coals of the Price formation. Around the margin of this formation is a 

 belt, varying in width, of Pulaski red shale, which dips in all cases away 

 from the center of the mountain at angles varying from 15° to 35°. From 

 the center of the mountain, erosion has removed the red shale and cut 

 deeply into the underlying Price sandstone. The outer margin of this 

 peculiar area was followed quite closely, excepting the eastern extremity, 

 east of the Christiansburg-Blacksburg road, in order to determine the 

 nature of the unconformity. Along this road nothing but the Pulaski 

 shale shows in a broad, flat-lying belt that terminates within a mile to 

 the eastward in a broad, rounded point. The line of contact is generally 

 marked by a belt of level land, in which no rocks are visible. On the 

 southern side, however, in the vicinity of Vickers switch, the contact is 

 along rather high land, but the same indefiniteness characterizes the 

 junction line. In but one place were the Pulaski shales and the Shen- 



XXIV— Bui.r.. Geol. Soc. Am., Voi.. 5, 1893. 



