342 Prof. A. C. Ramsay on Geological Ages 



fauna, as regards genera, with the exception of Labyrinthodontia and 

 the appearance of Pterosauria, is represented, pretty equally, through all 

 the remaining members of the Mesozoic formations, from Jurassic to 

 Cretaceous inclusive. After this comes the great Pachydermatous Mam- 

 malian Eocene fauna, and after that the Miocene fauna, which, in its 

 main characters, is of modern type. 



The'general result is that, from Jurassic to Cretaceous times inclusive, 

 there was a terrestrial fauna in these regions, chiefly Reptilian, Saurian, 

 and Marsupial, and, in so-called Cainozoic or Tertiary times, chiefly 

 Reptilian and Placental. In brief, the old continental epoch that lasted 

 from the beginning of the Old Red Sandstone to the close of the Trias, 

 locally embraces two typical land-faunas one Carboniferous and Per- 

 mian, and one Trias sic ; while the later epoch, from the beginning of the 

 Lias to the present day, also locally contained two typical land-faunas, 

 the latter of which is specially Placental. (See Table.) 



I am aware that such inferences are always liable to be disturbed by 

 later discoveries, and I therefore merely offer the above suggestions as 

 being in accordance with present knowledge. 



Another point remains. The earliest known marine faunas, those 

 of the Cambrian, Lingula-flag, and Tremadoc beds, include many of 

 the existing classes and orders of marine life, which are much more fully 

 developed in the succeeding Llandeilo and Bala strata, such as Spongida, 

 Annelida, Echinodermata, Crustacea, Polyzoa, Brachiopoda, Lamelli- 

 branchiata, Pteropoda, Nucleobranchiata, and Cephalopoda. This im- 

 portant fact was insisted on by Professor Huxley in his Anniversary 

 Address to the Geological Society in 1862. The inference is obvious, 

 that in this earliest known varied life* we find no evidence of its having 

 lived near the beginning of the zoological series. In a broad sense, com- 

 pared with what must have gone before, both biologically and physically, 

 all the phenomena connected with this old period seem to my mind to 

 be quite of a recent description ; and the climates of seas and lands were 

 of the very same kind as those that the world enjoys at the present day 

 one proof of which, in my opinion, is the existence of great glacial boulder 

 beds in the Lower Silurian strata of Wigtonshire, west of Loch Ryant. 



This conclusion, not generally accepted, has since been confirmed by 

 Professor Q-eikie and Mr. James Geikie, both with regard to the Wigton- 

 shire strata and to the equivalent beds in Ayrshire. In the words of 

 Darwin, when discussing the imperfection of the geological record of 

 this history, " we possess the last volume alone, relating only to two or 

 three countries ; " and the reason why we know so little of pre-Cambrian 

 faunas, and the physical characters of the more ancient formations as 

 originally deposited, is, that, below the Cambrian, strata we get at once 

 involved in a sort of chaos of metamorphic strata. 



* Earliest known except the Huronian Aspidella Terranovica and the Laurentian 

 Eozoon Canadense. 



t See Philosophical Magazine, vol. xxix. p. 289, 1865. 



