GEOLOGICAL SOCIETY. 



15 



in thickness, and seldom exceeding five or six inches, 

 occupy an aggregate thickness of probably 200 feet, at 

 the western termination of Shade mountain ; and the 

 quarries on the margin of the canal, within a mile of 

 Lewistown, furnish an inexhaustible supply of these 

 excellent paving materials. The vegetable forms are 

 less distinguishable when fresh from the quarry, than in 

 the weathered slabs and pavements, where the argilla- 

 ceous shale, which always interposes between the seams 

 of indurated stone, is decomposed and scaled off. 



In the foregoing notes have been brought together 

 the observations which a temporary residence near the 

 spot has enabled the writer to make, respecting this 

 singular depository of fossil plants ; to which investiga- 

 tion he is happy to acknowledge himself stimulated by 

 the instructive paper of Dr. Harlan on the Fucoides 

 Alleghaniensisy in the Journal of the Academy of Na- 

 tural Sciences of Philadelphia, vol. vi. p. 289. 



