Xlviii PHOCEEDINGS or THE GEOLOGICAL SOCIETY. 



in an address from the chair of this Socictj^*, which none of us have 

 forgotten, that nothing need at present be said about it ; the more, 

 as the considerations which have been laid before you have certainly 

 not tended to increase your estimation of such evidence. It will be 

 preferable to turn to the positive facts of palaeontology, and to in- 

 quire what they tell us. 



We are all accustomed to speak of the number and the extent of 

 the changes in the living population of the globe during geological 

 time as something enormous ; and indeed they are so, if we regard 

 only the negative differences which separate the older rocks from the 

 more modern, and if we look upon specific and generic changes as 

 great changes, which from one point of view they truly are. But 

 leaving the negative differences out of consideration, and looking 

 only at the positive data furnished by the fossil world from a broader 

 point of view — from that of the comparative anatomist who has 

 made the study of the greater modifications of animal form his chief 

 business — a surprise of another kind dawns upon the mind ; and 

 under this aspect the smallness of the total change becomes as 

 astonishing as was its greatness under the other. 



There are two hundred knowTi orders of plants ; of these not one is 

 certainly known to exist exclusively in the fossil state. The whole 

 lapse of geological time has as yet yielded not a single new ordinal 

 type of vegetable structure f. 



The positive change in passing from the recent to the ancient 

 animal world is greater, but still singularly small. No fossil animal 

 is so distinct from those now living as to require to be arranged 

 even in a separate class from those which contain existing forms. 

 It is only when wo come to the orders, which may be roughly esti- 

 mated at about a hundred and thirty, that we meet with fossil 

 animals so distinct from those now living as to require orders for 

 themselves ; and these do not amount, on the most liberal estimate, 

 to more than about ten per cent, of the whole. 



There is no certainly known extinct order of Protozoa ; there is 

 but one among the Ccelenterata — that of the rugose corals ; there 

 is none among the Mollusca ; there are three, the Cystidea, Blastoidea, 

 and Edrioasterida, among the Echinoderms ; and two, the Trilobita 

 and Eurypterida, among the Crustacea ; making altogether five for 

 the great subkingdom of Annulosa. Among Yertebrates there is 

 no ordinally distinct fossil fish : there is only one extinct order of 

 Amphibia — the Labyrinthodonts ; but there are at least four distinct 

 orders of Eeptilia, viz. the Ichthyosauria, Plesiosauria, Pterosauria, 

 Dinosauria, and perhaps another or two. There is no known extinct 

 order of -Birds, and no certainly known extinct order of Mammals, 

 the ordinal distinctness of the " Toxodontia " being doubtful. 



The objection that broad statements of this kind, after all, rest 

 largely on negative evidence is obvious, but it has less force than 

 might at first be supposed; for, as might be expected from the 



* Anniversary Address for 1851, Quart. Journ. Geol. Soc. vol. vii. 



t Sec Ilookor's * Introductory Essay to tho Flora of Tasmania,' p. xxiii. 



