Comparative Value of certain Geological Ages. 145 



the deposition of the Old Red Sandstone may have taken, when 

 compared with the time occupied in the deposition of certain 

 members of the Mesozoic formations. Through a series of argu- 

 ments, lithological, stratigraphical, and palseontological, the conclu- 

 sion is arrived at, that the whole of the Liassic and Oolitic series 

 present the various phases of one facies of marine life, and, in this 

 respect, are comparable to the changes in the fossil contents of the 

 various subformations of the Cambrian and Lingula-flag series, 

 of which the Tremadoc Slates form an upper member. In 

 like manner the Lias and Oolites may be compared with the 

 Lower Devonian strata; and therefore a lower portion of the Old 

 Red Sandstone may have talcen as long for its deposition as the ivhole 

 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 ivhole 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 tlie Jurassic, Wealden, and Cretaceous strata collectively. 



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

 Carboniferous epoch, is compared with the Eocene period, both 

 being locally of marine, estuarine, freshwater, and terrestrial 

 origin, and both connected 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 continent, 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 con- 

 clusion that the great local continental era, which began with the Old 

 Red Sandstone and closed with the JS r ew 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 Cai- 

 nozoic 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 nourished 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. Erom 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 

 LTpper Cretaceous strata of Aix-la-Chapelle and lasting to the pre- 

 sent day. 



In like manner the faunas connected with the land resolve them- 

 selves into two types : — the first chiefly Labyriuthodontmn, as shown 

 in the Carboniferous and Permian strata ; and the second charae- 



PML Mag. S. 4. Vol. 48. No. 310. Aug. 1874. L 



