SILURIAN ERA. 83 



the germ of life on some sunny and serene spot ; it may 

 charm the materialist to claim for Life the eternity he does 

 for Matter, by referring to a metaniorphism which is con- 

 tinuously obliterating the fossils in the deepest seated rocks ; 

 but the palaeontologist is debarred from such reveries, and 

 is bound down by a rigid chain of facts as they occur in 

 nature. He has traced life so early as the Cambrian slates j 

 should it be detected still lower, he is ready to accept it. 

 To him, in the mean time, the Metamorphic schists are a 

 tabula rasa; the Cambrian slates form his furthest verge 

 and boundary ; and the spirit of induction restrains him 

 within its limits. And, after all, fossil evidence itself is 

 greatly in favour of the view, that we have here attained, 

 or all but attained, the furthest limit of life. "We see it 

 increasing and spreading into higher and higher forms as 

 we ascend in the geological scale, and decreasing and nar- 

 rowing into lowlier forms as we descend : numerically the 

 forms are fewer, physiologically they become less important ; 

 and it is but fair induction to believe that in the few scat- 

 tered forms of Cambria we have all but reached the zero of 

 organic existence/* 



From the Cambrian the palaeontologist passes into the 

 Silurian age a period characterised by its lowly sea- weeds 

 and doubtful traces of land plants by genera and species 

 of protozoan, radiate, molluscoid, molluscan, and articu- 

 late types, but by few, if any, even of the lowest verte- 

 brate order. Its strata consist of shales, sandstones, con- 

 glomerates, and limestones the solidified muds, sands, 



* It is right to mention, however, that the tendency of recent dis- 

 covery is to carry the traces of life further and further back among 

 these slaty and semi-crystalline strata. The detection of new grapto- 

 lites and trilobites in the schists of Bray Head, Skiddaw, Bohemia, and 

 North America, is a fact too significant to be overlooked in geological 

 speculation. 



F 



