126 HISTORICAL GEOLOGY. 



While the inorganic history was still going on (although finished 

 in its more fundamental ideas), there was, finally, the intro- 

 duction of life, — a new and great step of progress. That life, 

 beginning with the lower grades of species, was expanded and ele- 

 vated through the creations of new types, until the history closed 

 in the appearance of Man. In this organic history there are suc- 

 cessive phases of progress, or a series of culminations, with the 

 creation of Man and Mind as the last and loftiest of these culmi- 

 nations. As the tribes, in geological order, pass like panoramic 

 scenes before us, the reality of one age after another becomes 

 strongly apparent. The age of Mammals, the age of Eeptiles, and 

 the age of Coal-Plants come out to view like mountains in the 

 prospect, — although if the mind should attempt to define precisely 

 where the slopes of the mountain end as they pass into the plain 

 around, it might be greatly embarrassed. It is not in the nature 

 of history to be divided off by visible embankments ; and it is a 

 test of the true philosopher to see and appreciate the culmina- 

 tions of phases in time, or of the successive ideas in the system 

 of progress, amid the multitude of events and indefinite blendings 

 that bewilder other minds. 



We note here the following important principles : — 



First. The reality of an age in history is marked by the culmina- 

 tion of some new idea in the system of progress. 



Secondly. The beginning of an age will be in the midst of a pre- 

 ceding age ; and the marks of the future coming out to view are to 

 be regarded as prophetic of that future. 



Thirdly. The end of an age may be as ill defined as its beginning, 

 although its culminant point may stand out boldly to view. 



Thus, the age of Coal-Plants was preceded by the occurrence of 

 related plants far back in the Devonian. The age of Mammals 

 was foreshadowed by the appearance of mammals long before, in 

 the course of the Keptilian age. And. the age of Eeptiles was pro- 

 phesied in types that lived in the earlier Carboniferous age. Such 

 is the system in all history. Nature has no sympathy with the art 

 which runs up walls to divide off her open fields. 



But the question may arise, whether a geological age is not, after 

 all, strongly marked off in the rocks. Eocks are but the moving 

 sands or the accumulations of dead relics of the age they represent, 

 and are local phenomena, as already explained. Each continent 

 has its special history as regards rock-making; and it is only 

 through the fossils in the rocks that the special histories are com- 

 bined into a general system. Movements have in all ages disturbed 

 one hemisphere without affecting the other, causing breaks in the 



