toward the 'sea between this point of the cliff, and that close to
the Pontinha, on the east. Of this we may easily satisfy ourselves,
by examining the direction of the basalt ridges which mark the
course of the streams, and the surface of the country behind, and
level with the cliff inland. For some distance, the cliff presents
nothing but the beds of tufa, scoriae, and pumice, in short, precisely
the same as the section drawn, taking away the beds of columnar
basalt; but a slip on the eastward terminates in the appearance of
scoriaceous basalt, beneath the yellow tufa, which has hitherto
formed the lowest bed of our section, and that, as if it were a
prolongation of the band of scoriae, and had forced its way through
the yellow tufa, thus,
The breadth of this stream of scoriaceous basalt, is about seventy
yards; the depth of the upper, or vaulted part, as seen in the
drawing, Plate 3, B, is about twenty feet, that of the lower part,
(which is composed of sheets and ridges running into the sea, and
dipping to the south, in an angle of 20°) is seldom more than four
feet. Beneath this scoriaceous basalt is red, passing into yellow
tufa, with a band of pumice, at the lowest visible part of the bed,
which is about ten feet deep when it is lost sight of: this lowest
tufa, scarcely discoverable in the cavernous part of the scoriaceous
basalt, is best seen in the break close to the left of the hut, in the
drawing.
The cells, of which this lower, or scoriaceous basalt is full, are
generally long and narrow; in a perpendicular section they appear
confused, but when the basalt has been cleft in an inclined plane,
parallel with its dip, it becomes evident, that these cells, (always