400 Notes on tfte Formation of extensive 



would seem to be checked at the gulf known as the Perte du 

 Rhone. 



As a general fact, it may be fairly stated that rivers, where 

 their courses are short and rapid, bear down pebbles into the 

 seas near them, as is the case with the torrents in the Mari- 

 time Alps ; but that when their courses are long, and changed 

 from rapid to slow, they deposit the pebbles where the force of 

 the stream diminishes, and finally transport mere sand or mud 

 to their mouths, as is the case with the Rhine, Rhone, Po, 

 Danube, &c. 



IV. Discharge of Rivers into Tidal Seas. 



Tidal rivers, when large, most frequently keep their mouths 

 open, though their is always a tendency to form bars and sand- 

 banks; as for example, the Thames, the Severn, the Seine, 

 the Loire, the Tagus, the St. Lawrence. In such situations, 

 the ditritus, if any, is small enough to be held in mechanical 

 suspension. 



Some tidal rivers, or rivers which discharge themselves into 

 tidal seas, form deltas when the force of the current is consi- 

 derable, the tides small, or the seas not much subject to storms 

 setting in shore, but merely to land and sea breezes. Of the 

 mouths of such rivers, the Mississippi, the Oronoco, the Ganges, 

 and the Yellow River of China, are examples. The detritus 

 brought down by such rivers to their mouths is either sand or 

 mud ; therefore they do not contribute towards the formation of 

 gravels at the bottom of the ocean. 



Tidal rivers, when small, have a tendency to be blocked up 

 by the sea, which often increases the bars into long banks of 

 pebbles or sand, and it is with difficulty that the rivers deliver 

 their waters into the sea; if the line of coast keeps the direction 

 of the prevalent winds, the difficulty is increased, and the river 

 generally gains a cliffor some hard ground, for one of its banks, 

 before itcan effectits escape into the sea. Good examples of these 

 embouchures are seen on our southern coast. The Teign has a 

 tendency to be blocked up by the bank upon which part of 

 Teignmouth is built, named the Den, which the easterly winds, 

 producing the greatest breakers on this beach, drives across 

 the mouth of the river from E. to W., and the Teign escapes 

 by the side of the Ness Point, which affords it support. The 

 Axe is also deflected from its course by the pebble bank thrown 

 up from W. to E by the prevalent W. and S.W. winds, which 

 here afford the heaviest breakers, and it escapes into the sea 

 by supporting itself against Axmouth cliff; the sea, however, 

 is constantly endeavouring to bar up its passage. 



The harbour at Shoreham is a good example of a river de- 

 flected from its straight course by banks thrown up by the sea. 



