fusedly in this conglomerate, beneath, and between the porous
basalt at Praia Formosa. To the eastward of Funchal, this conglomerate
matter increases in proportion, and is insinuated between
the more compact masses of basalt in vast patches, as if it had
flowed down, and been deposited at the same time with it. The
olivine of the compact basalt near the coast, and in the immediate
environs of Funchal, is generally granular; it was not evident in
any state in the scoriaceous basalt. I observed several pieces of
basalt in the walls about Madeira, containing mammillated carbonate
of lime; the mammillae about the size of small shot, generally
separate, and always in a cell, sometimes large enough to
contain several; so that they would appear to be infiltrations;
but I very rarely found it in the compact basalt near the sea, and
presume, these stones were broken from the fragments washed
down by the torrents from the interior. The fer oxydule principally
characterizes the red tufa (which indurates by exposure to
the air, and forms a building stone), though it sometimes affords
long flat prisms of common horneblende, and acts more powerfully
on the needle than the yellow, which sometimes contains small
glistening particles of feldspath : both give out innumerable bubbles
of air when put into water; but I shall have occasion to
describe them more particularly, when speaking of the best soils
for the vines of Madeira, and will only mention here, that when
the red tufa is in immediate contact with the porous basalt above
it, (as in the ravine descending to the beach) it is formed into
small pentagonal prisms, about 2 inches in length, and 1J in diameter;
in this case it is of a reddish brown, looks like a baked
clay, and its specific gravity is increased to 2.06. Some of the
pumice fragments (evidently not ejected until the scoriaceous
basalt had flowed and deposited itself), imbedded in the yellow
tufa of the ravine by which I descended to the beach, contained
minute crystals of horneblende ; its colour was yellowish, its structure
more frequently porous than cellular, rarely fibrous, (therefore
probably, not formed at a very considerable depth beneath the
surface of the globe), and it was always supernatant*. If I am not
mistaken, pumice has not hitherto been found with basalt ; when
I picked up a detached morsel on my landing, it led me to expect
a trachytic formation : I do, not think there is a trace of obsidian
in. the island, The scoriæ, especially in the inland sections, are
frequently coated with a shining matter, generally pale brown, but
sometimes black, and of a bituminous appearance ; it did not
detonate however with nitre, nor did it lose its colour or lustre at
a red heat. A grey crustaceous lichen ( idiothalames Ach.) covers
the porous and compact basalt, (in patches, ring within ring) and
is generally accompanied by another, equally crustaceous, but more
delicate in form, and of a deep orange. A third forms large light
coloured patches on the inland basaltic rocks, and is so abundant,
that in several instances it gives a different hue to that part of the
landscape“. All the lichens of Madeira are extremely interesting,
from their abundance or beauty; but, for the before-mentioned
reason, I have only been able to refer some of them to the great
divisions of Acharius. The methurn starts out from the rocks in
the same way as at Lisbon, and is found in great quantities on the
sea-shore; the ferula glauca is abundant. The only species of
cactus which can decidedly be pronounced indigenous, is the
c. opuntia, which only grows on the rocks nearest the seaw.
' M. Guillin, after a mere glance at Funchal and its bay, has not hesitated to assert,
“ que la lave qu’on trouve à Madere n’a aucune partie vitrifiée, ni aucune veritable
■pierre ponce.” See the Appendix of the V oydge de Btyry St. Vincent.
“ Genus, thallus crustaceus, pallidus. Seutellee cUbee, in thaUo centralis.
The recent shells which I found scattered over the black ferruginous sand, and
amongst the basaltic pebbles of the beach, were a murex, a tritonia ? (brown, with
darker stripes, and yellow lips) ; murex, (white).; a purpura, (dusky brown) ; a colom*
bella, (white) ; a broken specimen of the argronauta tuberculosa, and an avicula, fight
brown, mottled with black towards the beaks. The patella plicata abounds on the