1865.] Man and Nature. 161 



alternation of marine and fresh-water inhabitants. In all this there are 

 no important changes of the land surface. 



The control of dunes by man is effected either by forming them 

 originally by artificial means, by protecting them when natural, or by 

 removing them when that can safely be done. In some places a mere 

 artificial wall will give rise to a broad belt of dune. Thus, in 1610, 

 a wall of three or four miles in length, thrown across a tide-washed 

 flat between the Zuider Sea and the North Sea, occasioned the forma- 

 tion of rows of dunes a mile in breadth, and altogether excluded the 

 sea. Similar results have been obtained by mere plank walls and 

 screens of reeds. Where dunes already exist, they can be prevented 

 from advancing by planting certain grasses, creeping plants, and 

 shrubs, the Arundo arenaria being the most valuable. This plant 

 grows to the height of about two feet ; but its strong roots and their 

 rootlets extend forty or fifty feet tlirough the sand. The looser the 

 soil the better it thrives, and as soon as the sand ceases to drift it dies, 

 its roots fertilizing the sand and helping to form a vegetable mould 

 for forest planting, pasturage, and ultimately arable land. The leaves 

 of the Arundo are nutritious food for cattle and sheep ; its seeds feed 

 poultry ; cordage and twine are made from its fibres ; it thatches well, 

 and its roots are good fuel. So many valuable properties sometimes 

 check its main use as a safeguard against the drifting sands. The 

 beach-grass is an American representative of this plant. On the 

 French coast upwards of 100,000 acres of land have been reclaimed ; 

 and in other parts of Em-ope a very large area. 



Of trees to succeed the Arundo, none is better than the Pinus 

 maritima, where it will grow. Its resins yield, according to the 

 French returns, a clear profit of 20s. per acre per annum, exclusively 

 of the value of the timber. 



As the plains and dimes of sand on the European coasts are esti- 

 mated to amount to at least 20,000 square miles, it is evident that 

 much yet remains for human agency in this matter ; and as moving 

 sand is invariably mischievous, while fixed sands rapidly become pro- 

 fitable, the subject is one of extreme practical importance. 



Great public works — such as the cutting of marine isthmuses, con- 

 necting different drainages by canals, and diverting the course of 

 rivers — are occasionally, though very rarely, effected by man ; rarely, 

 that is, considering the number of cases in which engineering opera- 

 tions of this nature would alter the mode of communication between 

 distant lands. 



There cannot be a doubt that the successful carrying out of the 

 scheme for connecting the Mediterranean with the Red Sea, or that 

 across the Isthmus of Darien, would produce physical changes of the 

 greatest magnitude. Whether these would involve modifications of 

 the surface, is doubtful ; but so far as animal and vegetable life is 

 concerned, they could not fail to act. Even the Great Gulf Stream itself 

 might be induced so far to change its course by a wide channel 

 through Central America, as to alter entirely the whole climate of 

 Western Europe. But these are speculative and possible, rather than 



VOL. II. M 



