as items of Geological Time. 341 



shorter duration than the older continent mentioned above in italics ; and 

 which, to us, seems so ancient, when we think that the Alps and the Jura 

 had then no more than a rudimentary existence. 



There are other points that bear on the comparative value of 

 different epochs of geological time. During the older local continental 

 epoch there nourished four distinct floras, those of the Old Red Sand- 

 stone, Carboniferous, Permian, and Triassic series. Of these the first 

 three, notwithstanding considerable generic and complete specific differ- 

 ences, may yet be said to be of one Palaeozoic type. The Triassic flora, 

 as far as it is known, is of a mixed character, with generic affinities, how- 

 ever, that unite it more closely to the Jurassic flora than to that of the 

 Permian age. The whole series may therefore be considered as resolving 

 itself into two types the first extending from the Old E/ed Sandstone 

 to the Permian times, and the second belonging to the Trias. 



During the later period that elapsed, from the beginning of the 

 deposition of the Lias down to the present day, we have also four 

 distinct floras the first of Jurassic type, embracing the little we know 

 of the Neocomian flora ; the second, Cretaceous, which, as regards the 

 Upper Cretaceous strata of Aix-la-Chapelle and of Greenland, is to a 

 great extent of modern type ; third, an Eocene, and, fourth, a Miocene 

 fl ora the last three being closely allied, and the Miocene flora of Europe, 

 in its great features, being nearly indistinguishable, except in species, 

 from the kind of grouping incident to some of the modern floras of the 

 northern hemisphere. The whole of this series may, therefore, in 

 European regions, be also considered as resolving itself into two types 

 the first Jurassic, and the second extending from the later Cretaceous 

 times to the present day. In this respect, the analogy to the floras of 

 two types of the more ancient continent is obvious ; and, in both epochs, 

 this kind of grouping is clearly connected with the lapse of time, widen, 

 in my opinion, may for each be of approximately equivalent value. 



The evidence derived from terrestrial Yertebrata is not quite so simple. 

 In the Old Eed Sandstone none are yet known. In the Carboniferous 

 rocks all the known genera (fourteen in Britain) are Labyrinthodont 

 Amphibia. The same is the case, though the known genera are fewer in 

 number, with the Permian rocks, excepting two land-lizards of the genus 

 Proterosaurus. Labyrinthodonts seem to decrease still more in the number 

 of species in the Trias ; but Crocodiles appear, together with seven named 

 genera of land-lizards, two genera of Anomodontia (Dicynodon and 

 Rhynchosaurus'), three genera of Deinosauria, and two of Marsupial Mam- 

 malia. As far as we yet know, therefore, this ancient continental fauna 

 pretty nearly resolves itself into two types ; and, just as the Triassic 

 type of flora passed into Jurassic times, so the Triassic land-fauna 

 does the same. The oldest, or Palaeozoic, type (Carboniferous and Per- 

 mian) is essentially Labyrinthodontian, and the second, or Triassic is, 

 characterized by the appearance of many true land-lizards and other 

 terrestrial reptiles, together with marsupial mammals ; and this typical 



VOL. xxii. 2 D 



