216 THE OCEAN. 



creepers of the convolvulus fix on the surface. A number of plants, 

 whose frail stems are half buried in the sand, are, perhaps, con- 

 temporary with the dune itself;* perhaps even they existed before 

 mankind had a history. 



In this strife between the force of the winds and the power of vege- 

 tation, the definite issue depends at the same time on the climato- 

 logical conditions, the nature of the soil, the form of the shore, and 

 various other circumstances, among which we must rank, in the 

 first place, the havoc caused by men and animals. In South America, 

 on the shores of those tropical countries where the development of 

 plants is favoured, according to the seasons, by an extreme heat and 

 by torrents of rain, and where the sands contain a considerable pro- 

 portion of animal and vegetable remains, most of the dunes are 

 already fixed at a few j^ards from the sea by mimosas, cactuses, and 

 thorny trees. However, on the eastern shores of all the rivers of 

 equatorial Brazil, which discharge themselves near the mouths of the 

 Amazons, we see, even somewhat far from the sea, ranges of dunes 

 from 25 to 50 feet in height, which move incessantly, driven by the 

 breezes of the trade winds. f This mobility of the sands is undoubtedly 

 connected with this fact, established beyond question by Coutinho 

 and Agassiz, that the shores are depressed in that part of Brazil, and, 

 consequently, they incessantly change their form, so that the dunes 

 have not yet had time to be fixed. 



In Europe the flora of the sands is less rich than in equatorial 

 countries. On the coasts of Jutland it is composed of only 234 species 

 of plants, very insignificant for the most part,:J: and the " white " 

 dunes of the Danish peninsula, as well as those of Gascony and Hol- 

 land, have also not enough cohesion to resist the furious western 

 winds which assail them. It is probable, nevertheless, that even in 

 the countries of the temperate zone the modest herbaceous vegetation 

 of the sands of the coast could, after a certain lapse of centuries, 

 acquire the strength necessary to fix the dunes, and prepare, by the 

 slow accumulation of its remains, a vegetable bed, where large trees 

 would grow spontaneously. 



If it were not so, it would be difiicult to understand how all the 

 dunes of Europe were originally covered with forests. According to 

 the unanimous testimony of the ancient geographers, the woods ex- 

 tended to the sea-shore in those plains which are now the Nether- 



* Aug. Pyr. de Candolle ; Elie de Eeaumont, 



t Revue Maritime et Coloniale, 1866. 



X Andresen, Om Klitformationen ; Marsh. 



