30 Fucoides in the Transition Rocks 



about six miles, through " the Narrows;" that is, in a deep 

 narrow trough between the two sandstone ridges of Shade 

 Mountain and Black Log Mountain ; having, for the most 

 part, barely space for its channel. The great western turn- 

 pike road and the Pennsylvania Canal also pass through this 

 ravine ; being, for some distance, excavated out of the base of 

 the northern ridge, called Shade Mountain. In consequence 

 of these public works, many of the inferior strata are here 

 exposed ; and although, in the aggregate, they do not com- 

 prise a thirtieth part of the entire elevation, they are highly 

 interesting, in displaying beds of fossil i^uci in unexpected 

 abundance. 



These beds, where I first saw them extensively intersected, 

 consist of fine-grained compact white sandstone ; interstrati- 

 fied with greenish argillaceous seams, and some laminae of 

 black shale, both containing mica. Upon the upper surfaces 

 of the argillaceous slabs are disposed innumerable groups of 

 Fucoides. Above these layers, other courses, covered with 

 the same fossil plants, could be traced obscurely ; while masses 

 of hard sandstone, whose figured surfaces bore rude resem- 

 blance to the Gothic tracery of ancient sculpture, had evi- 

 dently fallen from much more elevated sites. 



Pursuing the examination farther eastward, the beds of 

 Fucoides were again laid bare, by the canal excavations, to 

 the height of 50 ft. above the Juniata. Here I counted seven 

 courses of them, comprised within the thickness of 4 ft. Among 

 the lower beds are some of white cherty sub-crystalline sand- 

 stone, and others composed of micaceous schistose sandstone, 

 whose upper surfaces were traversed by another species of 

 Fucoides, distinguished by their long curving stalks ; whilst 

 upon other argillaceous slabs a third description of fossil ioici 

 crossed each other in straight lines, resembling network. It 

 may be remarked, that no casts of shells, nor, indeed, any 

 other organic body, occur with these deposits. 



At another point, three miles eastward of that where I com- 

 menced tracing the i^ucus beds, numerous seams of fine white 

 sandstone, separated, as before, by thin courses of micaceous 

 shale and clay, are exposed. Some idea of the rapid succes- 

 sion of vegetable deposits will be conveyed, when it is men- 

 tioned that eight or ten were numbered within the space of 

 6 ft., some of them not exceeding 1 in. thick. The surface 

 of Shade Mountain is too much obscured, by its thick covering 

 of coarse debris, to enable an examination of its structure to 

 be satisfactorily pursued ; but there is reason to conceive that 

 these fossils occur at various elevations, besides those of which 

 I have spoken. I have observed them at 100 ft., 1.50 ft., 



