290 GEOLOGICAL CONTEMPORANEITY ix 



something enormous . and indeed they are so, if 

 we regard only the negative differences which 

 separate the older rocks from the more modem, 

 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 differ- 

 ences 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 compara- 

 tive 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 known orders of plants ; 

 of these not one is certainly known to exist ex- 

 clusively in the fossil state. The whole lapse of 

 geological time has as yet yielded not a single new 

 ordinal type of vegetable structure.^ 



The positive change in passing from the recent 

 to the ancient animal world is greater, but still 

 sinonlarly 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 we come to the 

 orders, which may be roughly estimated at about 

 a hundred and thirty, that we meet with fossil 



1 See Hooker's Introductory Essay to the Flora of Tasmania^ 

 p. xxiii 



