THE GEOLOGIST 



JAJSTUARY, 1860. 



THE COMMON^ FOSSILS OF THE BRITISH ROCKS. 

 By S. J. Mackie, F.G.S., F.S.A. 



(Continued, from vol. ]jage 427.) 



Chap. 7. — First Traces of tlie Succession of Life. — The Lower Silurian 



UoclvS. 



Obscure as are the animal remains of these old Lingnla-flags, the 

 traces of vegetation are yet more difficult to make out and to 

 describe. Easier, too, are they to describe than to figure ; for, mere 

 shallow impressions and stains as they are upon the cleaved rock, it 

 is easier to see their remote resemblances to some known forms than 

 to convey an idea of them by the finest lines that the graver will cut 

 upon the wood. And then how unsatisfactory to spend days in 

 elaborating the representation of a mere fragment, the very charac- 

 ters of which we are in doubt about. 



We shall shortly present our readers, however, with figures of the 

 most illustrative specimens we can obtain of those sea-weeds of 

 the primeval shores, the Cruziana semijplicata, the Chondrites (?) 

 acidangulus, and Chondrites (?) informis. 



In North Wales, near Tremadoc, an u.pper portion of the Lingula- 

 flags, consisting of dark grey or blackish schists with thin layers of 

 grit, has been made out by Mr. Salter. This upper zone, in addition 

 to the Linrjula Davisii and Agnostus jpisiformis, presents us with two 

 other forms of trilobites, Conocephalus invitus (Salter), and EUpso- 

 cephalus (?) depressus (Salter), with a bryozoan (plate ii.), the oldest 

 of the group yet known, supposed to be allied to Fenestella, and 



VOL, III. A 



