THE PAST AND FUTURE OF GEOLOGY. 



185 



in the contiuuity of life and of stratificiition tbau mark tbe lesser divis- 

 ions. As these on tbe whole severally exhibit a distinct fauna and flora, 

 we may conveniently consider them as periods, each having its own dis- 

 tinctive life, and the number of which in Great Britain we have taken 

 api)roximatively at thirty-eight. 



The number of species common to one i)eriod and another varies very 

 greatly; but taking theavernge of the sixteen divisions of the Jurassic 

 and Cretaceous series, of which the lists were, with a portion of th»)se 

 of the older series, given a few years since by Professor Kamsay,* we 



*Aiiiiiver8ary addressea for 18G:i aiul 18()4, Quarterly Journal Geological Society. 

 The tables were computed by Mr. Etberidge. 



