end of the Mytilus lithophagus, of a solen, moulds of varioussized
venuses; a valuta ; a turritella; a conus, like that at Lisbon,
the pecten mvMiradiatus, and the pecten glaber, (neither of which
species, I believe, have before been found in a fossil state) and
the fragment of a large white pecten, apparently the p. maximus.
Some of the cardia were imbedded with the valves thrown open,
and presented ridges like the ligaments, and even the orange
colour of several of the pectines was preserved, and there were
several impressions like arcee\ This limestone afforded no odour
when struck. I found a beautiful fossil nearer the beach, which
appears to me to be an echinanthus\ perhaps it had fallen from
above, with some of the fragments of this limestone, which,
with the other, supplies the kilns of Funchal. Above this shelly
limestone was about six feet of a fine-grained, indurated sandstone,
deposited in layers, with projecting ledges, and acquiring a sco-
riaceous appearance, and dark-grey colour on the outer surface,
from exposure to the atmosphere, but presenting an orange-brown
within, and effervescing. On this rested a conglomerate, about
fifty feet deep, of nodules of wakke, of a lesser portion of the
orange-coloured ferruginous sand, and of small fragments of wakke,
emerging like nail-heads, and coated (with the exception of the
upper surface) with an indurated grey clay ; which also lines
small cavities in a mammillated form. No part of this conglomerate
effervesced, but it was covered by a shallow horizontal
bed of sandstone, of the same nature as that above the fetid
limestone.
Through all these different horizontal masses, (that is, from the
ad * ® ! solenes’ wrdia,. and pectines, may be said, from their greater abundance, to
characterize this rock. The calcareous breccias of Araya, near Cumana, contain
solenes, pectines, and ampullana, (Humboldt, Relation Historique, 1. 2, c. 5); the
latter are only found in the sandstone at Porto Santo.
1 An affinis, e. cucurbites ?
summit of the table land, of which this island is principally
formed, to the sea, a depth of about 240 feet) descend, more or less
perpendicularly, numerous basaltic dikes, sometimes jutting out
like walls, and serving as rude stairs .in the ascent, at others, nearly
even with the surface of the various rocks they intersect, and frequently
running parallel with the beach for some distance, at the
water’s edge, and forming rude piers. In some parts, their surface
was covered with considerable patches of a dull coralloidal carbonate
of lime, and in the basalt of the dikes on the north side, (for it was
the eastward face which afforded me the section I have described)
I found beautiful crystals of nepheline. A composita (flosculosus)
with white decomposed leaves, a ligneous stem, and flowers borne
in large close panicles, characterized the whole of this limestone
island; the absence of the florets prevented me from determining
i t ; the involucra were polyphyllous, and the receptacles covered
with silky hairs. Several small masses of the spongia officinalis lay
on the beach.
The peaks of tufa in the north-eastern part of Porto Santo, are
capped with a basalt approaching to phonolite, (which, if I mistake
not, has been found to cap the basaltic mountains of Bohemia and
other parts of Europe) by its lighter colour, numerous vitreous
crystals of felspar, decomposing crystals of common hornblende,
and lesser specific gravity, 2.15; but it yielded no particular
sound like phonolite, and its lamellar structure deviated in one
instance into large pentagonal columns ; immediately beneath this
capping of lighter basalt, appear the dikes, which descend through
the tufa to the sea; the upper parts of these dikes (sometimes
elevated 1600 feet above the sea), are generally of an earthy brown,
ferruginous appearance, but as they approach the sea, the basalt
becomes of a dark grey colour, and in the north-eastern point of
the island, especially, near Reo da Cruz, it is studded with large,
but imperfect, crystals of basaltic hornblende. In descending by