OF A FORMER WORLD. 21 



fishes we have evidence of this formation having been pro- 

 duced, not instantaneously, but through a long succession 

 of ages. Each bed of pebbles, if the ancient agencies of 

 nature were any way analogous to the present, must have 

 been the work of many years. That these agencies were 

 not more violent, or at least that there were long intervals 

 of repose, is attested by^fie beds of fine grained sand- 

 stone, and consolidated mud, with which the conglome- 

 rates alternate. The largest of our existing rivers, in 

 rainy seasons, carry great quantities of gravel, sand and 

 mud, into their estuaries or the sea ; but great as the amount 

 of debris is, the production of a quantity of matter, any 

 way equivalent to the old red sandstones of England and 

 Scotland, could not take place except in the lapse of innu- 

 merable ages. The mud carried down by the Nile, and de- 

 posited, amounts only to a quarter of an inch thick annually. 

 The old red sandstone formation is estimated at from three 

 to four thousand yards in thickness. Allowing a quarter 

 of an inch as the average annual aggregation of matter, 

 this formation alone could not have been deposited in less 

 than 432,000 years. 



If we contemplate for a moment the agencies that must 

 have been engaged in wearing down the surfaces of the 

 ancient rocks, and in transporting them over the vast areas 

 they now occupy, the time here stated will not seem any 

 way exaggerated, but far too little for the amount of the 

 effects produced. We have mentioned the old, red sand- 

 stone formation as an instance, from which something like 

 an idea may be formed of the time requisite for the produc- 

 tion of a certain class of rocks. The same, or even still 

 more decisive proofs of the lapse and change of time are 

 afforded by the other formations. 



To disintegrate to any considerable extent a solid rock 

 to transfer the material by a river-current to any oceanic 

 site to deposit it, and consolidate the deposition, are exces- 



