SOURCE OP ST. Peter's river. 19 



from the time at which the transition formations were pro- 

 duced, until the coal and its accompanying strata had com- 

 menced to be formed. We observe, in most cases, that 

 the slate and reddish sandstone occupy the base of the 

 higher mountains, and constitute the whole of the lower 

 ones ; while the crest of the high hills is formed of a sand- 

 stone which in every respect resembles that of the coal for- 

 mations. There seems likewise to be a difference in the 

 organic remains contained in these rocks, for in the lower 

 ones there are but vegetable impressions, (chiefly stems,) 

 while in the superior strata, shells belonging to the genus 

 Terebratula or Productus, are very frequently met with. 



We had an opportunity of ascertaining that the slate 

 which occupies the whole valley of the Potomac, in this 

 district, varies in its dip ; sometimes inclining to the south- 

 east, and at other times to the north-west. In one spot we 

 observed the change in the dip produced by a very gentle 

 undulation, without any derangement or interruption in 

 the stratification. Overlaying this slate, there is a lime- 

 stone of a blueish colour, presenting signs of organic re- 

 mains, and constituting Martin's Hill, which is one of the 

 highest in the range. This limestone appears at first to be 

 horizontally stratified, after which it assumes an inclined 

 position, and on ascending becomes nearly vertical, while 

 the top of the hill is crowned with large masses of lime- 

 stone, quite free from stratification, and presenting only a 

 very irregular division. Upon the summit of the mountain 

 the limestone is cavernous, and contains many organic re- 

 mains, among which the Terebratula and Productus are 

 chiefly discernible. It is filled with veins of crystalline car- 

 bonate of lime, which in some places assumes regular forms. 



From Cumberland to Wheeling the geology of the 

 country is much simplified. The coal formation predomi- 



