24 Tertiary Fossils. 



river, but even to a surprising number of the marine mollusca, 

 artieulata, and radiata. Our knowledge, therefore, of the 

 living creation of any given period of the past may be said 

 to depend in a great degree on what we commonly call chance, 

 and the casual discovery of some new localities rich in peculiar 

 fossils may modify or entirely overthrow all our previous ge- 

 neralizations, so long as they are based on the supposed non- 

 existence at former epochs of the fossil representatives of 

 large families or classes of plants and animals. 



Tertiary/ Fossils. 



When we contrast the botany and zoology of primary and 

 secondary strata with those of tertiary formations, it is more 

 especially incumbent on us to make due allowance for a com- 

 paratively deficient acquaintance with the ancient deposits, 

 which are more and more exclusively marine in proportion 

 as we depart farther from those periods during which our 

 existing continents were built up. They are more marine, 

 not because the ocean was more universal in times past, but 

 because, when we carry back our retrospect to epochs so dis- 

 tant that entire continents have been since submerged, we 

 are less favourably placed for exploring strata thrown down 

 in lakes and estuaries, or near the shore. In studying the 

 tertiary strata, as I before remarked, we have opportunities 

 of becoming more thoroughly acquainted with the remains of 

 the flora and fauna which flourished in a great variety of sta- 

 tions ; and besides, in these more modern rocks the imbedded 

 fossils are less obliterated by the destroying hand of time. 

 If we conceal or extenuate such circumstances when we argue 

 with an opponent who believes that the primary or secondary 

 fauna was as highly developed as the tertiary, we take an 

 unfair advantage of him ; not duly conceding how much the 

 chances of finding examples of terrestrial mammalia are on 

 our side. " We throw with loaded dice," to borrow an ex- 

 pression of Dr Fleming's, in a controversy respecting the 

 evidences of a tropical climate at more ancient periods. 



Of the tertiary mammalia, the oldest yet found, perhaps, 

 are those of the lower eocene, occurring in the London clay 

 of Sheppey and the sand of Kyson, near Woodbridge. Al- 

 thougli the species are as yet few in number, the quadru- 



