28 Fucoides in the Transition Rocks 



closely applied side by side at the commencement, and gra- 

 dually diverge towards their distal extremities. 



" In every case the stalks divide into two or more branches ; 

 the latter are more or less wrinkled, apparently according to 

 age, the rugae being more or less obsolete in the largest, pro- 

 foundly developed in the smaller or younger specimens. The 

 plants are fractured in many places and in various directions; 

 but the fractured portions do not display any evidence of 

 organisation ; nor is there any appearance of leaves, nervures, 

 or fructification." 



I believe that a fossil of this description has not been 

 noticed in any part of the transition series in Great Britain ; 

 yet, as some traces may be discovered through the aid 

 afforded by an accurate illustration, I am induced to transmit 

 some further notice of this fossil plant and of its geological 

 position. 



Mr. De la Beche enumerates two or three species of Fu- 

 coides in the grauwacke group of Europe. How near they 

 may approach to the fossil which is so strikingly character- 

 istic of a part of the same group in North America, I have no 

 present means of ascertaining. The two species found in the 

 transition limestone of Canada are dissimilar to the Fucoides 

 alleghaniensis. 



The aggregate thickness of the grauwacke group is enor- 

 mous in Pennsylvania; its breadth being about 120 miles, and 

 its stratification being inclined at a very high angle, and often 

 approaching to verticality, it is not improbable that the entire 

 mass averages forty-five degrees. I have examined a large 

 portion of this in detail, and have constructed a transverse 

 section of about seventy miles, from which it appears that in 

 about half this breadth the inclination of the rocks is towards 

 the Alleghany chain, and in the other portion it is reversed. 

 On the details of the subordinate portions of this group it is 

 not my intention to enlarge. It is sufficient to observe, gene- 

 rally, that they consist of arenaceous, slaty, and limestone 

 rocks, subdivided into innumerable varieties of siliceous and 

 argillaceous beds, conglomerates, shales, clays, marbles, flinty 

 slate and flinty limestone ; and include numerous coal seams, 

 both of anthracite and of the quality which may be termed 

 bituminous anthracite, and large deposits of iron, both argil- 

 laceous and haematitic. 



The surface of this region is broken into an infinite number 

 of sandstone ridges and limestone valleys, all running parallel 

 with the mountain chain of the Alleghany. 



These ridges are generally 700 or 800 feet above the 

 valleys, and are incapable of cultivation. Thev are covered. 



