146°" SPECIAL FEATURES 
economic point of view being the archil lichen from 
which the dye called litmus is obtained. Darwin 
describes this lower zone as uninviting in the extreme, 
the scanty brushwood leaving the black basaltic lava 
exposed, and giving the district the appearance of an 
iron-smelting region in the ‘ black country ’ of England. 
But the clouds hang low, and above an elevation of 
about eight hundred feet not only is there abundant 
rain during the rainy season, but even at other seasons 
a constant mist keeps the vegetation fresh. The plants 
of the two regions differ fundamentally, and in the 
upper cultivated plants from many climates thrive. Of 
the native vascular plants, about one-half are peculiar 
to the islands. The group consists of five principal 
and eight small islands, with a total area of nearly 
3,000 square miles. The hills range in height from 
3,000 to 4,000 feet. The more conspicuous bushes and 
trees are species of euphorbia, cactus, and acacia, 
so that the islands generally resemble savanas and 
desert regions in their vegetation. Palms are entirely 
absent. 
Turning now to the fauna, we find that mammals are 
practically absent. There are two mice, but of these 
one belongs to the widely distributed genus Mus, and 
has doubtless been introduced ; the other belongs to 
a South American genus (Hesperomys), and has also 
possibly been introduced. That there is nothing in the 
conditions of the islands to prevent the existence of 
even large herbivorous mammals is, however, shown by 
the fact that goats, pigs, horses, &c., introduced by 
man, have become wild, and have multiplied exceed- 
ingly. 
The birds present some interesting features. About 
seventy species, according to Wallace, have been 
