312 



UNIFORMITY OF CHANGE 



[Ch. XIV. 



state of science, it is chiefly by the aid of shells that we are 

 enabled to arrive at these results, for of all classes the tes- 

 tacea are the most generally diffused in a fossil state, and may 

 be called the medals principally employed by nature, in re- 

 cording the chronology of past events. In the Upper Miocene 

 rocks (No. 5 of the table p. 139) we begin to find a considerable 

 number, although still a minority, of recent species, inter- 

 mixed with some fossils common to the preceding, or Eocene 



epoch. We 



arrive at the Pliocene strata, in which 



man 



and in the newest of which nine-tenths of the fossils agree 

 with species still inhabiting the neighbouring sea. It is in 

 the Post-tertiary strata, where all the shells agree with spe- 

 cies now living, that we have discovered the first or earliest 



& 

 i remains 



some of v 



om 



member 



the Tertiary system we meet with many chasms, but none 

 which separate entirely, by a broad line of demarcation, one 

 state of the organic world from another. 



There are no signs 



termination 



om 



of one fauna and flora, and the 

 starting into life of new and wholly distinct forms. Although 

 we are far from being able to demonstrate geologically an 

 insensible transition from the Eocene to the Miocene, or even 



it fauna, yet the more we enlarge 

 and perfect our general survey, the more nearly do we ap- 

 proximate to such a continuous series, and the more gradually 

 are Ave conducted from times when many of the genera and 

 nearly all the species were extinct, to those in which scarcely 

 a single species flourished which we do not know to exist at 

 present. Dr. A. Philippi, indeed, after an elaborate com- 

 parison of the fossil tertiary shells of Sicily with those now 



Mediterr 



the result of his 



examination, that there are strata in that island, which attest 

 a very gradual passage from a period, when only thirteen m 

 a hundred of the shells were like the species now living in 

 the sea, to an era when the recent species had attained a 

 proportion of ninety-five in a hundred. There is, therefore, 

 evidence, he says, in Sicily of this revolution in the animate 











i 





7 













u 









