ITS DATES. 75 



action; and while the Creator has permitted the human 

 intellect to investigate and determine the one, we may rest 

 assured that the same intellect is yet destined to discover 

 the amount and duration of the other. In the mean time, 

 all that geology attempts is to arrange the formation of 

 the earth's crust into so many provisional stages each 

 stage representing an indefinite amount of time, but em- 

 bracing such stratified deposits as indicate a contempor- 

 aneity of origin, and are characterised by a general simi- 

 larity of organic remains. In this case, each .stage repre- 

 sents the sediments of a certain period, and is necessarily 

 characterised by its own peculiar fossils every change of 

 sea and land not only giving rise to new sediments, but to 

 altered conditions of vital existence, that are inevitably fol- 

 lowed by a modification of the flora and fauna. And sum- 

 ming up the whole, we are presented with the outline, at 

 least, of a grand and continuous evolution of vitality. Here 

 there may be local imperfections in the record there the 

 characters may be fragmentary and obscure ; but in the 

 main the broad features of world -history are sufficiently 

 obvious, and these systems and formations (provisional as 

 they may be) enable the geologist to give intelligible ex- 

 pression to the line and order of occurrence. 



Proceeding upon the basis of this arrangement, let us 

 now inquire into the nature of the Plants and Animals 

 preserved in these successive formations. Were they con- 

 structed on the same plan, and destined to perform analo- 

 gous functions in the economy of nature, with those that 

 now live and flourish around us 1 Or if differing in type, 

 what the amount of that difference, and the presumable 

 function which that difference implies] If race after race 

 has come and departed, what the conditions that accom- 

 panied their advent, and what the causes which apparently 



