LICHENS. . 129 
the populous world we had well-nigh forgotten, 
reminds us of the enjoyments and affections of 
home, and more than all, raises our thoughts to 
the Maker of the great and the small, who placed 
it there to cheer by its presence the lonely 
wilderness, and whose wondrous skill and good- 
ness its every petal, leaf, or frond declares in 
language, silent and unuttered, yet more eloquent 
than a thousand words. 
Some species of lichens are confined to certain 
geological formations. Stereocaulon paschale is the 
first vegetation that appears on lava when it cools 
and hardens. On Etna, Vesuvius, Hecla, and the 
Canary Islands it occurs so plentifully as to 
whiten the volcanic rocks with its tufted coral- 
like masses. It is not confined to lava, however, 
for it is often found on different kinds of rocks 
in sub-alpine districts, although as a rule it prefers 
trappean, porphyritic, and other rocks of igneous 
origin. One lichen, the Exdocarpon sinopicum, is 
found only on yellow hone schist, or on micaceous 
stones in walls that are strongly impregnated 
with iron; its own rusty colour resembling the 
red stone called sinoper, and looking as though it 
had been stained with the oxide of iron in its 
matrix. Some lichens prefer granite, others flint 
and quartz, others calcareous rocks, others mica- 
ceous schist, and others sandstone and slate; and 
I 
