180 ARE SOILS ENRICHED, IMPOVERISHED, pt. nr. 



fossil. For if nature filled the Adriatic at a dead level, 

 what signifies it to Ferrara ? But give it a slope from 

 Otranto to the foot of the Alps, and Ferrara must be- 

 come subterranean. 



I only talk of general tendencies. In such river 

 basins as have been mentioned, these operations are on 

 so vast a scale, they are spread over such vast spaces 

 of space as Avell as of time., they are so liable to disorder 

 from particular accidents^ such as changes of the course 

 of the river, extraordinary floods, landslips, earth- 

 quakes, subsidences, upheavals, partial destruction of 

 deltas by the sea, &c., &c., that man, unable to see 

 what is or what has taken place., can only speculate on 

 what must be, or what must have taken place. 



The sea eiids every valley, but never yet began 

 one ; that is, where there is no delta, when the river 

 and the tides have done their utmost, it is the sea 

 which prevents the farther deepening of the estuary. 



The force of the river, as it dies off in the sea, 

 becomes as perfectly horizontal as the force of a marine 

 current ; and neither of them could form an inch of 

 sloping valley. But where there are no currents to 

 prevent it, the sea, by stopping the longitudinal rush 

 of rivers, allows the deposit of deltas, and may thus 

 be said to prolong valleys. 



' Bottle off the sea,' and all estuaries and their 

 valleys will be deepened ; for the tidal part of each 

 river will be a torrent on the brow of a mountain. 

 In this case deltas and alluviums would disappear ; but 



