1874.] Comparative Value of certain Geological Ages. 147 



Old Red Sandstone may have taken as long for its deposition as tlie whole 

 of the time occupied in the deposition of the Jurassic series. 



Following out this train of argument through the Neocomian and 

 Cretaceous strata, the result is arrived at that the ivliole of the time 

 occupied in the deposition of the Old Red Sandstone may have been equal 

 to the whole of the time occupied in the deposition of all the Jurassic, 

 Wealden, and Cretaceous strata collectively. 



In the same manner the next term of the Continental era, the Carboni- 

 ferous epoch, is compared with the Eocene period, both being locally 

 of marine, estuarine, freshwater, and terrestrial origin, and both con- 

 nected with special continental epochs. Next comes the Permian series, 

 comparable in its lacustrine origin to the Miocene strata of so much of 

 Europe, though in the case of the Permian waters the lakes were salt. 

 After this the Triassic series of Europe alone remains of the old con- 

 tinent, the marine and salt-lake strata of which are not likely to have 

 taken a shorter time in their deposition than the older Pliocene strata. 



If the foregoing method be of value, we arrive at the general conclusion 

 that the great local continental era, which began with the Old Red Sandstone 

 and closed with the New Red Marl, is comparable, in point of Geological Time, 

 to that occupied in the deposition of the whole of the Mesozoic series later than 

 the New Red Marl, and of all the Cainozoic formations, and, more probably, of 

 all the time that has elapsed since the beginning of the deposition of the Lias 

 down to the present day ; and consequently the more modern continental era, 

 which locally began with the Eocene period and lasts to the present day, 

 has been of much shorter duration. 



The author then pointed out that during the older continental era 

 there flourished two typical floras one extending from the time of the 

 Old Bed Sandstone to the close of the Permian strata ; while the second, 

 which is largely of Jurassic type, characterized the Triassic formations. 

 From the time of the Lias onward in time, we have also two distinct 

 typical floras the first of Jurassic, and the second of much more modern 

 type, beginning with the Upper Cretaceous strata of Aix-la- Chapelle and 

 lasting to the present day. 



In like manner the faunas connected with the land resolve themselves 

 into two types : the first chiefly Labyrinthodontian, as shown in the 

 Carboniferous and Permian strata ; and the second characteristic of the 

 Trias, with Crocodilia, many land-lizards, Anomodontia, Deinosauria, and 

 Marsupial Mammalia. This fauna, as regards genera, with the exception 

 of Labyrinthodontia and the appearance of Pterosauria, is represented 

 through the remaining members of the Mesozoic formations, from 

 Jurassic to Cretaceous inclusive. After this comes the Pachydermatous 

 Mammalian Eocene fauna, and after that the Miocene land-fauna, 

 which, in its main characters, is of modern type. From Jurassic to Cre- 

 taceous times, inclusively, there was therefore, as far as we know, in 

 this area a land-fauna chiefly Keptiliau, Saurian, and Marsupial, and 



VOL. XXII. M 



