of North America. 



29 



to the thickness of from 10 to 100 feet, with huge blocks of 

 sandstone. Upon their steep sides few traces of vegetable soil 

 exist ; yet the oak, the chestnut, the pines, and several other 

 trees, Iiave obtained a firm footing, and have extended over 

 the loftiest crests. Embarrassed with this accumulation of 

 debris, the geologist seeks, almost in vain, for some exposed 

 face, some unencumbered surface, to determine the arrange- 

 ment and structure of these vast and singularly prolonged 

 masses. He finds as much difficulty in viewing the details of 

 their geological features, as in obtaining, from amidst the 

 ancient forests which overshadow them, an uninterrupted view 

 of the wide-spread landscape beneath his feet. 



I have observed Fucoides alleghaniensis, at points 150 miles 

 remote from each other, in the sandstone ridges that occur 

 parallel with the eastern side of the Alleghany Mountains; but 

 nothing resembling them can be detected in the intermediate 

 limestone valleys. The subject of my sketch {Jig> 6.) was 



derived from the vicinity of this place [Lewistown], on the 

 banks of the Juniata River, and in the same district from 

 which Dr. Harlan's specimen was procured. Detached 

 fragments, rolled from the mountains, and fallen slabs, exhi- 

 biting fine specimens of this fossil, are not unfrequently met 

 with amidst the talus of the ridges ; but it is only very recently 

 that thfe beds in which it occurs in situ came under my observ- 

 ation. Under the conviction that these vegetable strata have 

 hitherto escaped geological notice, I' proceed to detail some 

 circumstances relating to their position. 



After passing Lewistown, the Juniata flows easterly, for 



