148 THE HABITABLE EAETH OEIGINALLY WOODED. 



grown with, wood as the most fei*tile plain, though, for obvious 

 reasons, the process 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 sm'face of the 

 rocks they cover; they arrest and confine the dust wliich the 

 wind scatters over them, and their final decay adds new material 

 to the soil abeady haK formed beneath and upon them. A very 

 thin stratum of mould is sufficient for the germination of the 

 seeds of hardy evergreens and birches, the roots of which are 

 often found in immediate contact with the rock, supplying the 

 trees with nourishment from a soil deepened and enriched by the 

 decomposition of their own foliage, or sending out long rootlets 

 into the surrounding eartli in search of juices to feed them.* 



The eruptive matter of volcanoes, forbidding as is its aspect, 

 does not refuse nutriment to the woods. The refractory lava of 

 Etna, it is true, remains long barren, and that of the great erup- 

 tion of 1669 is still almost wholly devoid of vegetation.f But 

 the cactus is making inroads even here, while the volcanic sand 



* One of the best examples I can call to mind of the spontaneous action of 

 nature, in re-clothing with vegetation rock and earth once denuded of it, is in 

 the Canale della Pieve, below Feltre. This gorge is inclosed by high and 

 often precipitous cliffs, whose surface is in a state of disintegration favorable 

 to the growth of plants and shrubs, and the faces of very steep rocks, long 

 bared of all vegetation, are now covered with verdure to a surprising extent. 

 If the goat and other browsing animals can be excluded for a few years, 

 these mountains, steep as they are, will be clothed with a luxuriant growth of 

 shrubs and trees. 



f Even the volcanic dust of Etna remains very long unproductive. Near 

 Nicolosi is a great extent of coarse black sand, thrown out in 1669, which, for 

 almost two centuries, lay entirely bare, and can be made to grow plants only 

 by artificial mixtures and much labor. 



The increase in the price of wines, in consequence of the diminution of the 

 product from the grape disease, however, has brought even these ashes under 

 cultivation. " I found," says Waltershausen, referring to the years 1861-63, 

 "plains of volcanic sand and half -subdued lava streams, which, twenty years 

 ago, lay utterly waste, now covered with fine vineyards. The ash-field of ten 

 square miles above Nicolosi, created by the eruption of 1669, which was en- 

 tirely barren in 1835, is now planted with vines almost to the summits of 

 Monte Rosso, at a height of three thousand feet." — Ueber den Sicilianisehen 

 Ackerbau, p. 19. 



