THEORY OF THE EARTH. 135 



that our actual downs, or sand-hills, have begun 

 to be blown up by the winds. And, dating from 

 the same epoch, colonies of the human race must 

 have then begun, for the first or for the second 

 time, to spread themselves, and to form new estab- 

 lishments in places fitted by nature for their re- 

 ception. 



I do not here take the action of volcanoes in- 

 to the account, not only because of the irregula- 

 rity of their eruptions, but because we have no 

 proofs of their not having been able to act below 

 the sea ; and because, on that account, they can- 

 not serve us as a measure of the time which has 

 elapsed since its last retreat. 



MM. Deluc and Dolomieu have most carefully 

 examined the progress of the formation of new 

 grounds by the collection of slime and sand wash- 

 ed down by the rivers; and, although exceeding- 

 ly opposed to each other on many points of the 

 theory of the earth, they agree exactly on this. 

 These formations augment very rapidly ; they must 

 have increased with the greatest rapidity at first*, 

 when the mountains furnished the greatest quan- 

 tity of materials to the rivers,* and yet their extent 

 still continues to be extremely limited. 



* One instance will be found appended to this Essay, of modern 

 alluvial formations proceeding with considerably increased rapidity. 



