THE GEOLOGIST. 
JANUAUY, 1860. 
THE COMMON FOSSILS OP THE BRITISH ROCKS. 
By S. J. Mackie, F.G.S., F.S.A. 
(Gontitmed from vol. \i.,page 427.) 
Chap. 7. — First Traces of the Succession of Life. — Tlie Lower Silurian 
Bocks. 
Obscure as are the animal remains of these old Lingula-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 om' readers, however, with figures of the 
most illustrative specimens we can obtain of those sea-weeds of 
the primeval shores, the Cruziana semvpUcata, the Ghond/rites (?) 
acutangulus, and Ghondrites (?) informis. 
In North Wales, near Tremadoc, an upper 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 Lingula ~^avisii and Agnosias j)isiformis, presents us with two 
other forms of trilobites, Gonocephalus mvitus (Salter), and Elipso- 
cephalus (?) depressus (Salter), with a bryozoan (plate ii-), the oldest 
of the group yet known, supposed to be allied to Fenestella, and 
\oh. in. A 
