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202 THE OCEAN.
CHAPTER XXV.
OBSTACLES OPPOSED BY NATURE TO THE PROGRESS OF DUNES.—FIXATION
OF THE SANDS BY SEEDS.
The work of nature is, however, double; and if on one side she hastens the advance of the sands, on the other she attempts to arrest them.
She herself points out the means of prevention, or else prevents spontaneously the disasters of which she is the cause. In certain places, and especially on a part of the coasts of the Landes, she exercises a physical
and chemical action by employing the oxide of iron which the water contains to consolidate the sands and transform them gradually into actual
rocks. Elsewhere organic cements, composed of broken shells and remains of silicious and calcareous infusoria, agglutinate the arenaceous
particles, and give them the necessary stability to resist the winds. But
these means of consolidating the sands are exceptional. It is principally
vegetation which fixes the moving hills on the sea-shore. On almost all
coasts the sandy and calcareous debris of the soil contain enough fertilizing principles to nourish a certain number of hardy plants, which do not
fear the salt air of the sea, and which send down their roots to a great
depth, so as to absorb the necessary moisture. Among these hardy vegetables the commonest, and most useful at the same time, is Marram-grass
(Arundo arenaria), whose slender and flexible stems can hardly arrest
the wind, but whose strong roots, sometimes twelve or fifteen yards Jong,
develop all the better the less consistence the sand has. Various species
of convolvuli creep over the ground, and fixing their vigorous cordage
from place to place, sometimes envelop an entire dune in their net-work of
leaves and flowers. Other plants rise more proudly, but if their stem is
buried in the sands they transform it into a root, and give birth to a new
shoot, which may be interred in its turn, without the plant being in danger of perishing. Thus such a seed germinating at the base of the dune
often produces a plant which ends by spreading to the summit of the
mountain, and fastens by a cable of roots the arenaceous strata which the
creepers of the convolvulus fix on the surface. A number of plants,
whose frail stems are half buried in the sand, are perhaps contemporary
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 vegetation, the definite issue depends, at the same time, on the climatological
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
* Aug. Pyr. de Candolle; Elie de Beaumont.
| Title | The ocean, atmosphere, and life |
| Creator | Reclus, Elisée |
| Publisher | Harper |
| Place of Publication | New York |
| Date | 1873 |
| Language | eng |
| Type | Books/Pamphlets |
| Title | 00000225 |
| Type | Books/Pamphlets |
| Transcript | 202 THE OCEAN. CHAPTER XXV. OBSTACLES OPPOSED BY NATURE TO THE PROGRESS OF DUNES.—FIXATION OF THE SANDS BY SEEDS. The work of nature is, however, double; and if on one side she hastens the advance of the sands, on the other she attempts to arrest them. She herself points out the means of prevention, or else prevents spontaneously the disasters of which she is the cause. In certain places, and especially on a part of the coasts of the Landes, she exercises a physical and chemical action by employing the oxide of iron which the water contains to consolidate the sands and transform them gradually into actual rocks. Elsewhere organic cements, composed of broken shells and remains of silicious and calcareous infusoria, agglutinate the arenaceous particles, and give them the necessary stability to resist the winds. But these means of consolidating the sands are exceptional. It is principally vegetation which fixes the moving hills on the sea-shore. On almost all coasts the sandy and calcareous debris of the soil contain enough fertilizing principles to nourish a certain number of hardy plants, which do not fear the salt air of the sea, and which send down their roots to a great depth, so as to absorb the necessary moisture. Among these hardy vegetables the commonest, and most useful at the same time, is Marram-grass (Arundo arenaria), whose slender and flexible stems can hardly arrest the wind, but whose strong roots, sometimes twelve or fifteen yards Jong, develop all the better the less consistence the sand has. Various species of convolvuli creep over the ground, and fixing their vigorous cordage from place to place, sometimes envelop an entire dune in their net-work of leaves and flowers. Other plants rise more proudly, but if their stem is buried in the sands they transform it into a root, and give birth to a new shoot, which may be interred in its turn, without the plant being in danger of perishing. Thus such a seed germinating at the base of the dune often produces a plant which ends by spreading to the summit of the mountain, and fastens by a cable of roots the arenaceous strata which the creepers of the convolvulus fix on the surface. A number of plants, whose frail stems are half buried in the sand, are perhaps contemporary 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 vegetation, the definite issue depends, at the same time, on the climatological 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 * Aug. Pyr. de Candolle; Elie de Beaumont. |
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