18 EXPEDITION TO THE 



apparently very ancient formation, and which we feel in- 

 clined to refer to the red sandstone formation, occurs. It 

 frequently acquires a reddish colour, and being in great 

 measure composed of quartz, assumes in some places the 

 appearance of an eisenkiesel. Its stratification is very dis- 

 tinct, extending from north-east to south-west and dipping 

 to the north-west. This stratification is not visible oa 

 both sides of the mountain. The eastern slope being car- 

 ried upon the crests of the strata, which are very brittle, a 

 sort of soil is soon formed from the fragments of the rock, 

 which entirely conceals it from view, but on the western 

 slope it is very well marked. On the summit of the hill, 

 numberless fragments of trap rock are strewed in every 

 direction. To the west of this ridge we again strike the 

 clay-slate, which continues along the valley of the Potomac, 

 being interrupted by the appearance of the blue limestone 

 in the traverse valleys of the Big and Little Conolaway 

 Creeks. This slate differs very much from that described 

 aliove as constituting the North mountain. The latter is a 

 quartzose, the former an argillaceous slate ; and the differ- 

 ence of dip is sufficient to distinguish them. 



This clay-slate is formed of alternate layers of a very 

 shistose mass and a more compact one. The layers vary 

 in thickness, many of them however not exceeding a few 

 inches. In the more compact layers there are indications 

 of a globular structure consisting of concentric shales. 



The slate is soon succeeded by a sandstone, which 

 constitutes several of the mountains known by the local 

 appellations of the Sideling, Town-hill, &c. It is not 

 possible to determine with precision the spot at which the 

 sandstone of coal formations commences, indeed we think 

 it probable that no such limit exists in nature. The pro- 

 cess may have continued without any marked interruption. 



