586 MANUAL OF NATURAL HISTORY. 



suits of recent earthquakes, as on the coast of Chili 

 and at the mouth of the Indus. In the Mediter- 

 ranean is a terrace or raised beach fifty feet above 

 the level of the sea, and abounding in shells of the 

 present date. Submarine forests of trees belonging 

 to species still living, are sometimes found below the 

 level of the sea, as on some of the coasts of Great 

 Britain, the estuary of the Tay, and in the North 

 of France. They owe their unusual position either 

 to the encroachment of the sea, or to partial depres- 

 sion of the land Marine Silt comprises those re- 

 cent accumulations of sand, mud, and clay, collected 

 by the tide and waves, and altering the outline of 

 promontaries and bays, or filling up fens and marshes. 

 The Isthmus of Suez has by this means doubled its 

 width since the time of Herodotus ; Tyre and Sidon, 

 once sea ports, are now several miles inland ; and 

 large districts in Holland are modern formations of 

 the existing seas. 



Submarine accumulations are formed by currents 

 from the poles to the equator, carrying with them 

 rocks and gravel, embedded in icebergs, which gra- 

 dually form strata at the bottom of the sea. The 

 mud, carried out by great rivers, produces the same 

 effect as in the Yellow Sea, the Gulf of Mexico, and 

 the Caribbean Sea. In the German Ocean enormous 

 shoals are found, as the Dogger-bank, destined, per- 

 haps, in future ages, to form new islands. The 

 various Deltas, as those of the Ganges, Rhine, and 

 Nile, are triangular islands, or mud-flats, formed 

 also by alluvial deposits of mud ; they gradually be- 



