GEOLOGICAL SOCIETY. 



7 



After passing Lewistown, the Juniata flows easterly 

 five or six miles, between two ridges of siliceous rock, 

 each upwards of 700 feet high, through the narrows. 

 So narrow indeed is this ravine for the most part, that 

 it only suffices for the channel of the river. The west- 

 ern turnpike road, and the Pennsylvania canal are 

 chiefly formed out of the base of the Shade Mountain, 

 which rises on the north side. In making the excava- 

 tions for these works, the arrangement of the lower strata, 

 is consequently exposed. This developement is the 

 more interesting, since it comprises the beds which con- 

 tain fossil fuci in singular abundance. 



October 2d, and 25th. Commencing the examination 

 from the west, I traced these beds uninterruptedly 

 among the debris, for a couple of miles, to a position 

 where they could be examined more satisfactorily. 



They consisted of compact, fine grained argillaceous 

 sandstone, interstratified with greenish seams of shale 

 and some with their laminse of dark carbonaceous slate, 

 both containing mica. Further westward, the fucus beds 

 were again laid bare, to the height of near fifty feet. 

 Here I counted seven courses of them, comprised within 

 a thickness of only four feet. 



Among the lower beds are some of white sub-crys- 

 talline quartz rock, and others of micaceous and schis- 

 tose sandstone, whose upper surfaces were traversed by 

 fuci of another species, distinguished by long curving 

 stalks ; whilst on other slabs a third species, crossing 

 in straight lines, formed a reticulated surface, resem- 

 bling network. 



