APPENDIX. 107 



earth's physical history*. How little do we know of 

 the Faunas and Floras even of those countries whose 

 spoils now constitute the dry land of the south-east of 

 England ! For example, no traces of Infusoria have been 

 detected in the Wealden strata, though diligent search 

 has been made by competent observers; yet no naturalist 

 will doubt that the mollusks and crustaceans, ( Cyprides), 

 found in those fluviatile deposits, fed upon fresh- water 

 animalcules, like their recent congenors; and it is pro- 

 bable, that, sooner or later, fossil Infusoria will be dis- 

 covered in the Wealden formation. The following remark 

 of Mr. Lyell is in accordance with the opinions above 

 expressed: — "It is too common a fallacy to fix the era of 

 the first creation of each tribe of plants or animals, 

 and even of animate beings in general, at the precise 

 point where our present retrospective knowledge happens 

 to stop t-" 



A similar fallacy pervades the ingenious speculations 

 as to the relative depths in the ocean in which certain 

 strata were originally deposited, as indicated by the 

 presence or absence of particular species of shells; the 

 geographical and vertical range of their presumed living 

 analogues being taken as the data upon which these 



* See '' The Medals of Creation, Vol. II, p. 872. 

 f Lyell' s Travels in North America. 



