VEGETATION IN VOLCANIC MATTER. 
131 
propagation of trees may all be negatively expressed and 
reduced to these three : exemption from defect or excess of 
moisture, from perpetual frost, and from the depredations of 
man and browsing quadrupeds. Where these requisites are 
secured, the hardest rock is as certain to be overgrown with 
wood as the most fertile plain, though, for obvious reasons, the 
pr ocess is slower in the former than in the latter case. Lichens 
and mosses first prepare the way for a more highly organized 
vegetation. They retain the moisture of rains and dews, and 
bring it to act, in combination with the gases evolved by their 
organic processes, in decomposing the surface of the rocks they 
cover; they arrest and confine the dust which the wind scat¬ 
ters over them, and their final decay adds new material to the 
soil already half formed beneath and upon them. A very thin 
stratum of mould is sufficient for the germination of seeds of 
the hardy evergreens and birches, the roots of which are often 
found in immediate contact with the rock, supplying their 
trees with nourishment from a soil derived from the decompo¬ 
sition of their own foliage, or sending out long rootlets into 
the surrounding earth in search of juices to feed them. 
The eruptive matter of volcanoes, forbidding as is its as¬ 
pect, does not refuse nutriment to the woods. The refractory 
lava of Etna, it is true, remains long barren, and that of the 
great eruption of 1669 is still almost wholly devoid of vegeta¬ 
tion.* But the cactus is making inroads even here, while the 
volcanic sand and molten rock thrown out by Vesuvius soon 
more than a hundred hectares, not one pine is found uninjured by them.”— 
Revue des Deux Mondes , Mai, 1863, p. 157. 
Beckstein computes that a park of 2,600 acres, containing 250 acres of 
marsh, 250 of fields and meadows, and the remaining 2,000 of wood, may 
keep 364 deer of different species, 47 wild boars, 200 hares, 100 rabbits, 
and an indefinite number of pheasants. These animals would require, in 
winter, 123,000 pounds of hay, and 22,000 pounds of potatoes, besides 
what they would pick up themselves. The natural forest most thickly 
peopled with wild animals would not, in temperate climates, contain, upon 
the average, one tenth of these numbers to the same extent of surface. 
* Even the volcanic dust of Etna remains very long unproductive. 
Nhar Nicolosi is a great extent of coarse black sand, thrown out in 1669, 
