m i
AND PORTO SANTO. 7
verbascim thapsum, until I had ascended two-thirds of the way,
or about 1400 feet above the sea, where they disappeared: the
thymus vulgaris continued a little further. The scilla maritima
(in great beauty), the daphne gnidium (very flourishing but
dwarfish), the carduus acaulis, thé eryngium tenue, the anethum
segetum (which seems to start out of the clefts of every rock,
yielding an unpleasant odour), continued from the foot of the
ascent to within a few feet of the summit. Two solitary plants
of the dipsacus fullonum grew about three-fourths of the way up,
and just beyond them appeared the echium vulgare, thinly scattered.
The limestone only varied in its tints of the exterior surface,
which sometimes looked as if it had been covered with a mixture
of soot and ochre, and presented longitudinal furrows, resembling
woody fibres. I discovered no fetid odour on striking the different
masses, nor any trace of fossil remains ; but the nodules
of silex which it contained, evidently of cotemporaneous origin,
were frequent, and deeply impregnated with lime : occasionally
portions of common jasper, and, more rarely, of agate, were imbedded.
About half way up, I walked over vast sheets of this
limestone, more compact, mottled, and seemingly harder than
the rest;, they were hewing it into mill-stones. The hillocks
which bordered the ascent were formed of detached pieces of silex
and lime imbedded in a loose earth : there appeared to be a breccia
of the same nature, not only above the limestone, but in one
instance intersecting it horizontally, in shallow beds. In the
lowest rocks, especially in the quarry north of the aqueduct, the
mass more frequently appeared crystalline, and once afforded
me prismatic crystals, the more compact masses adjoining which
were sometimes so happily sprinkled with green dots as to appear
dendritic. The highest point immediately west of the aqueduct,
and affording a view of the mouth of the river, still presented