BoA MADEIRA. 
It is a remarkable fact, that notwithstanding the number of dikes 
here seen, the layers intersected by them were not dislocated. 
Degradation—Decomposition.—The valleys of Madeira are nearly 
free from debris at the base of the lofty cliffs. This is so different 
from what is seen in our own country, that at first it struck us as a 
very singular fact, especially as the alternation of tufaceous and com- 
pact layers of rock expose the precipices to rapid wear; but it is fully 
explained by the absence of frosts, and was afterwards found to be a 
common characteristic of the igneous islands of the Pacific. Another 
cause may consist in the rapid formation of soil over the declivities, 
the growth of vegetation forming a protection against degradation. 
There is soil and verdure even on the fronts of the most precipitous 
bluffs, wherever there is a cleft or a projecting shelf for their lodg- 
ment; and many a large tree may be seen clinging with its roots to 
the side of some perpendicular height, far beyond the reach of man. 
The warm climate, and the abundant mists that envelope the summits 
of the island, are both favourable to the rapid growth of vegetation. 
LIMESTONE OF CANICAL AND ST. VINCENT. 
Incrustations and spherical concretions of carbonate of lime are found 
at various places along the coast, above high water mark, where they 
are apparently formed by depositions from the sea-water thrown up 
as spray. Along Brazen Head the scoriaceous rock, in some places, 
was covered with globules of carbonate of lime, one-sixteenth of an 
inch in diameter. Just east of Camera de Lobos, the incrustations 
were, in some places, half an inch thick, and they presented the usual 
banded colours of stalagmite, arising from the gradual deposition of 
successive layers. 
The Canical limestone is situated just beyond the village of Cani- 
cal, near a small chapel dedicated to ‘“ Nostra Sefora da Piedade,” 
which stands on a cliff facing the sea, (see figure 3, preceding page.) 
We landed from our boat just beyond this elevation, and after a few 
minutes’ walk up a sandy hill, reached the deposit. It borders both 
sides of a low valley, which cuts obliquely across the point of land 
forming this extremity of Madeira. The uppermost limit is an even 
horizontal line on both sides; on the southern side this line is about 
one hundred feet above the sea, while, on the northern, it is consider- 
