Ixxviii PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



and upper sections of the great mesozoic period. But the gap be- 

 tween palaeozoic and mesozoic, although the link be not altogether 

 broken, is vastly greater than any other of the many gaps in the 

 known series of formations. I am one of those who hold, u priori, 

 that all gaps are local, and that there is a probability at some future 

 time of our discovering gradually somewhere on the earth's crust 

 evidences of the missing links. All our experience and knowledge, 

 theoretical and practical, warrant the affirmation that at every known 

 stage of geological time there were sea and land. Even those who 

 believe in a primaeval azoic period will hardly sanction the supposition 

 that there has been any repetition of azoic epochs since the first life- 

 bearing sera commenced. And if so, and if there were always sea and 

 land since the commencement of the first fossiliferous formation, we 

 are warranted in assuming that both earth and water had their floras 

 and their faunas. All geological experience goes to show, that wherever 

 you have a perfect sequence of formations accumulating in the same 

 medium, air or water as the case may be, there is, if not a continuance 

 of the same specific types, a graduated succession and interlacement 

 of types and of the facies of life-assemblages : even as on the present 

 surface of the earth the faunas and floras of proximate provinces in- 

 termingle more or less specifically, or, if physical barriers prevent the 

 diffusion of species, assume more or less one general facies. This 

 passage, by aspect and type, of one stage in time into another is but 

 scantily indicated at present in the uppermost manifestations of the 

 palseozoic life and the lowermost of the mesozoic. The missing links 

 will sooner or later reward the diligence of the geological explorer. 



But in the general aspect of the palaeozoic world, contrasted with 

 the worlds of life that followed, although all are evidently portions 

 of one mighty organic whole, there seems to me to be something more 

 than the contrast that depends on the loss or non-discovery of con- 

 necting links. There is more than we can explain by this theory. 

 Granting for its support all facts capable of being so applied, there 

 are residual phaenomena to be accounted for, and which as yet have 

 not been referred to any law that I know of. 



For some years I have lived in hope of the discovery of a palaeozoic 

 fauna and flora more in accordance with those of after-epcchs than 

 those we know, and fondly fancied that local differences of physical 

 conditions alone might account for the discordance. But the fields 

 opened by IVIurchison, Sedgwick, and Phillips have been so extended 

 and have yielded such rich harvests at the hands of James Hall and his 

 fellow-explorers in America, and of Barrande, de Koninck, de Verneuil, 

 the Romers and Sandbergers, M'Coy, King, Salter, Eoualt, and many 

 other able palaeontologists who have worked at palaeozoic fossils in 

 Europe, that it is becoming evident that we have before us a fair and 

 true image of at least the marine aspect of the primaeval group of 

 faunas. The more they are investigated, the wider the ground "s 

 explored, the more striking is the difterence in the main between the 

 life palaeozoic and the after-hfe. 



Doubtless a principal element of this difference lies in substitution 

 — in the replacement of one group by another, serving the same pur- 



