98 Geological Epochs. 



in either case. In the latter, certain remarkable events 

 induce us to break it into periods, characterised by special 

 events, which were always led up to gradually by broad 

 changes of power or of opinion. In the former, there 

 are often great breaks in the chain of geological history r 

 which, locally, are not filled up by stratigraphical 

 deposits, and which under these circumstances form 

 definite geological epochs, while in other cases (as in 

 Civil history), the change of conditions was so great in 

 given areas, that the new series of events may be locally 

 classed as constituting new geological epochs. This is 

 eminently the case when we attempt to realise the 

 history of the Old Bed Sandstone, as locally and physic- 

 ally distinct from that of the Contemporaneous Devonian, 

 strata. 



