OP CREATION. 255 



If we consider the case of the British Islands 

 generally, it appears very clear that the great earth- 

 quake movements resulting in elevation, which have 

 chiefly left marks of their long-continued action, were 

 of two principal geological periods : those of the first 

 period commencing about the middle of the deposit 

 of the coal, and lasting till the upper beds of new 

 red sandstone were deposited; and those of the 

 second period, not beginning till after the close of 

 the deposit of the upper chalk of Britain, but lasting 

 throughout the formation of the beds of London 

 clay. Since, also, these two periods of disturbance 

 are those at which the most marked difference seems 

 to have taken place in the nature of animal and 

 vegetable existence, we are justified in believing that 

 the frequent succession of disturbances during these 

 periods rendered certain parts of the earth not capa- 

 ble of maintaining their former inhabitants, and that 

 the disturbances lasted so long that the species sub- 

 sequently introduced were of very different specific 

 character. 



Before the commencement of the secondary epoch 

 we must suppose that there existed some consider- 

 able tract of land to supply the abundant deposits 

 of woody matter which have since become coal, 

 and the sinking down of this land, and consequent 

 frequent exposure of a fresh surface to the ravages of 

 the sea, may account for the rapid deposition and 

 peculiar character of the new red sandstone, and also 

 of its successor the lias ; and I have stated the pro- 

 bability that the oolitic strata were deposited in an 

 ocean bed, sinking during the early and middle part, 

 but rising towards the close, until, at length, at the 



