320 Siluria—Present State of Geology. 
essential modifications of those which remained, it still bore a strong 
resemblance, through its plants and animals, to the Carboniferous 
period ; whilst, in unison with all the great facts elicited by our 
survey of the older strata, it was marked by the appearance of 
an animal of a higher grade than any one in the foregone eras—a 
large thecodont reptile—allied (according to Owen) to the living 
Monitor. 
“In speaking of the Silurian, Devonian, Carboniferous, and Per- 
mian rocks, let me however explain, that whilst each of the three 
latter groups occupy wide spaces in certain regions, no one of them 
is of equal value with the Silurian, in representing time or the suc- 
cession of animal life in the crust of the globe. When the Silurian 
system was divided into lower and upper parts, our acquaintance 
with younger formations simply sufficed to show a complete distinc- 
tion between its animal remains as a whole and those of the car- 
boniferous rocks, from which it is separated by the thick accumula- 
tions of the Old Red Sandstone. At that period the shelly, slaty 
rocks of Devonshire, were not known to be the equivalents of such 
Old Red Sandstone; still less had the relations and lime contents of 
the strata now called Permian been ascertained. Judging from the 
fossils then collected, it was believed, that the Lower Silurian con- 
tained organic remains, very distinct from those of the Upper Silu- 
rian; and yet the two groups were united in a system, because they 
were characterised throughout by a common facies. This so called 
system was, in short, typified by a profusion of Trilobites and Grap- 
tolites, with Orthides and Pentameri of a type wholly unknown in 
the carboniferous rocks. And whilst fishes were seen to exist in the 
intermediate masses of Old Red Sandstone, no traces of them could 
be detected below the very uppermost zone of the Silurian rocks. 
Nineteen years have elapsed, and after the most vigilant researches 
in various regions of both hemispheres, these great features remain 
the same as when first indicated. The labours, however, of those 
who followed me, have infinitely more sustained the unity of that 
system,* for its lower and upper divisions are now proved to be con- 
nected, not only by such generic types and analogous forms, but 
further by the community of a very considerable number of identical 
bodies. 
‘In a broad classification of primeval life, one eminent naturalist t 
views the Devonian, Carboniferous, and Permian rocks as simply 
the Upper Paleozoic; the Silurian rocks constituting the Lower 
* See the works of John Phillips, E. de Verneuil, Edward Forbes, Joachim 
Barrande, James D. C. Sowerby, James Hall, J. W. Salter, D. Sharpe, T. 
Davidson, John Morris. The most. recent researches in Britain give the large 
number of nearly 100 species of fossils, common to the Lower and Upper Silu- 
rian. 
t+ Edward Forbes. 
