§ 18. FOSSILS OF THE SILURIAN SYSTEM. 783 



in the Silurian deposits, and of these, one hundred are 

 also present in the Devonian formation ; but only fif- 

 teen species are common to the whole palaeozoic epoch, 

 and not one is known in any of the newer deposits. These 

 remains almost exclusively belong to the invertebrata, the 

 relics of fishes being comparatively rare ; the large develop- 

 ment of this class of vertebrated animals in the Devonian 

 strata above, is a remarkable zoological character of that 

 epoch, for the general forms of the Silurian fauna, with 

 this exception, are also found in that system. 



Vegetables. — In England, and on the Continent of Europe, 

 imperfect traces of Fucoids are the only vegetable remains 

 hitherto observed in strata older than the Devonian ; nor 

 has any coal or carbonaceous matter been discovered, except 

 small nests of culm or anthracite. The most ancient shales 

 and sandstones of Scandinavia and Russia contain fuci 

 only, and these rocks are considered by Sir R. Murchison 

 as forming the limit where the phenomena of organization 

 stop.* For as these lowermost Silurian deposits with 

 fucoids, rest upon pre-existing crystalline rocks without 

 fossils, it has been assumed that they indicate the first 

 appearance of organic creation : an inference which, in the 

 present state of our knowledge, is in my opinion wholly 

 inadmissible. 



Mr. Lyell, with his accustomed sagacity, has taken a 

 more just and comprehensive view of this question. He 

 observes, f that from the absence of all terrestrial vegetation 

 and fresh-water shells, it has been inferred that but a small 

 extent of dry land, if any, existed at the Silurian epoch. 

 " But if we colour on a map of the globe those spots over 

 which the Silurian strata have been hitherto traced, and 

 consider the insignificance of their extent in comparison 

 with the surface of our planet, we shall instantly perceive 



* Geology of Kussia. f Elements of Geology, vol. ii. p. 172. 



