GEOLOGICAL SOCIETY. 



9 



were counted in the thickness of only three feet. 

 There seems to be more than a hundred and fifty leet 

 thickness of this part of the series. It is difficult to 

 estimate the entire thickness, since it cannot be known 

 how low it descends under the level of the Juniata. 

 Allowing for the average inclination of the whole group 

 from the river to the ridge, it cannot be taken at less 

 than 200 feet. At the west end of Shade mountain I 

 found these beds extending uninterruptedly to an ele- 

 vation of from 300 to 350 feet. Those containing the 

 obscure algse reached 250 feet, and at 300 feet abun- 

 dance of surface slabs exhibited the Fucoides Mlegha- 

 niensis in situ. Above this height the ridge is abrupt 

 and is covered with loose sandstone blocks. 



The deposit which has been thus briefly traced out, 

 although it forms an insignificant fraction of the im- 

 mense succession which is comprised within the grau- 

 wache group, presents matter for the consideration of 

 the speculative geologist. It has been seen that here 

 occur almost innumerable beds of fucoides, of several 

 species. 



Hence may be inferred the existence at various 

 epochs, of so many surfaces on which vegetation 

 flourished, at the bottom of an ancient ocean. We 

 ascertained that there were frequent repetitions of these 

 submarine plants, and many renewals of the argillaceous 

 matter in which they took root. We further learn, 

 from the often repeated successions of this marine ve- 

 getation, and from the absence of the coarse aggre- 

 gates, grits and conglomerates, that this member of the 

 Vol. I.—B 



