182 M. r! CAMPBELL — PALEOZOIC OVERLAPS IN VIRGINIA. 



erous sediments upon the limestone. This hypothesis agrees better with 

 the known facts than any theory of faulting yet proposed. The condi- 

 tion necessary for such a deposition is a depression in the limestone 

 along the axis of what is now Price mountain and the occupation of 

 this depression by probably an arm of the sea. When this depression 

 occurred and whether there are other formations below the Price sand- 

 stone of course can only be conjectured, but it seems probable that the 

 sedimentation in this basin was limited to Carboniferous times. In this 

 depression, formed by local folding of the strata, the original mantle of 

 soil would probably be preserved and the newly deposited material 

 would be laid down upon it. This sedimentation culminated with the 

 deposition of the Pulaski shale ; consequently today around the margin 

 we find an unbroken la5^er of this shale in contact with — not the lime- 

 stone but the limestone soil that had been formed previous to the subsi- 

 dence. The elevation that closed the period of sedimentation in this 

 basin must have occurred immediately after the Pulaski shale was de- 

 posited, for it seems hardly possible that any later formation was deposited 

 on this area and subsequently eroded, for in such a case either there 

 would be found remnants of that formation or the red shales would have 

 been cut away by the great erosion necessary to remove its cover. So 

 the period of elevation and probable folding would appear to have been 

 contemporaneous with the formation of the Carboniferous limestone over 

 the adjoining areas, and from the same fact its effect would seem to have 

 been local and of short duration. 



There is an apparent difficulty in the way of accepting this hypothesis, 

 and that is in the character of the sediments found in the different basins. 

 The strata in Price mountain cannot be distinguished from those of Brushy 

 mountain or the area west of Pulaski. This would seem to indicate a 

 continuous deposit over the entire area rather than deposition in local 

 basins. Again, the entire absence of so-called shore phenomena, such 

 as conglomerates and other coarse sediment is particularly noticeable- 

 While it is impossible for us to restore the exact conditions under which 

 these sediments were deposited, we are safe in assuming that the imme- 

 diate land-area was composed of the Shenandoah limestone, and in all 

 probability would soon be reduced to baselevel, and then would be a 

 neutral element in the question of sedimentation ; the sands and clays 

 washed down by the streams would furnish the material, and under such 

 conditions the sea margin would be free from cliffs, and so the strata 

 then forming would be free from conglomerates and all coarse sediments, 

 except sandstone, deposited by the ocean currents ; but the whole ques- 

 tion of sedimentation is at present in a state of such obscurity that it is 

 almost impossible to say what should and what should not have been 



