454 UPPER SILURIAN BONE-BED. [Ch. XXVII. 



generalization," adding, " the Silurian system, therefore, may be regarded 

 as representing a long early period, in which no vertebrated animals had 

 been called into existence." 



It is certainly a fact well worthy of our attention, that as yet no re- 

 mains of fish are on record as coming from any stratum older than the 

 base of the " Upper Ludlow." (See above, p. 432.) When we reflect on 

 the number of Mollusks, Echinoderms, Corals, Trilobites, and other fossils 

 already obtained from Silurian strata below " the Ludlow," we may well 

 ask, whether any other set of fossiliferous formations were ever studied 

 with equal diligence and over so vast an area without yielding some 

 ichthyolites. 



Nevertheless, we must be permitted to hesitate before we accept, even 

 on such evidence, so sweeping a conclusion, as that the globe, for ages 

 after it was habitable by all the great classes of invertebrata, "emained 

 wholly untenanted by vertebrate animals. In the first place, we must 

 remember that we have detected no insects, or land-shells, or freshwater 

 pulmoniferous mollusks, or terrestrial crustaceans, or plants (except fu- 

 coids), in rocks below the Upper Silurian. Their absence may admit of 

 explanation, by supposing all the deposits of that era hitherto examined to 

 have been formed in seas far from land or beyond the influence of rivers. 

 Here and there indeed a shallow-water, or even a littoral deposit may 

 have been met with, -as in North Wales, for example, and North America ; 

 but, speaking generally, the Silurian deposits, as at present known, have 

 certainly a more pelagic character than any other equally important for- 

 mations. 



It is a curious fact, and not perhaps a mere fortuitous coincidence, that 

 the only stratum which has yielded the remains of land-plants is also the 

 only one which has afforded the bones of fish. Bone-beds in general, 

 such as that of the Lias near Bristol, those of the Trias near Stuttgardt, of 

 the Carboniferous Limestone near Bristol and Armagh, and lastly that of 

 the " Upper Ludlow," are remarkable for containing teeth and bones, 

 much rolled and implying transportation from a distance. The associa- 

 tion of the spores of Lycopodiacese (see. p. 432) with the Ludlow fish- 

 bones shows that plants had been washed from some dry land, then 

 existing, and had been drifted into a common submarine receptacle 

 with the bones. More usually, however, the " Upper Ludlow," like 

 the " Lower Silurian," is devoid of plants and equally destitute of ich- 

 thyolites. 



It has been suggested that Cephalopoda were so abundant in the Si- 

 lurian period that they may have discharged the functions of fish ; to 

 which we may reply that both classes coexisted in the Upper Siluiian 

 period, and both of them swarmed together in the Carboniferous and 

 Liassic Seas, as they do now in certain parts of the ocean. We may also 

 suggest that we are too imperfectly acquainted with the distribution of 

 scattered bones and teeth, or the skeletons of dead fish on the floor of the 

 existing ocean, to have a right to theorize with confidence on the absence 

 of such relics over wide spaces at former eras. 



