of which were
formed of scoriae which had fallen back again in a pasty condition, and
had become soldered together, the fourth consisting of a pyramidal block
of compact and lithoidal lava, which appeared to have been forced up by
impetus from the ground beneath. A little smoke issued from the small
crater, and a loud hissing from the interior was audible. By lying
along the edge, I could see a cavity of cylindrical form about ten
metres in depth, tapestried with stalactitic scoriae covered with
sublimations of various colours. The bottom of this crater was level,
but in the centre a small cone of about two metres had formed, pointed
in such a manner that it possessed but a very narrow opening at the
apex, from which smoke issued with a hissing sound, and from which were
spurted a few very small incandescent scoriae. This little cone increased
in size as well as activity until it filled the crater, and rose four or
five metres above the brim.[A] New and more abundant lavas appeared near
the base of this cone, and, pouring continually into the Atria del
Cavallo, rushed into the Fossa della Vetrana in the direction of the
Observatory and towards the Crocella, where they accumulated to such an
extent as to cover the hill-side for a distance of about 300 metres;
then turning below the Canteroni, they formed a hillock there without
spreading much farther. These very leucitic lavas are capable of great
extension, the pieces which are ejected forming for the most part very
fine filiform masses, which may be collected on the mountain in great
quantities, and specimens of which I presented to the Academy under the
name of _filiform lapilli_. These threads were often of a clear
yellowish colour, and, when observed under the microscope, were found to
consist of very minute crystals of leucite embedded in a homogeneous
paste. The crystals were still smaller as the diameter of the threads
was less, and never formed knots or swellings even in the most hair-like
threads. These observations led me to reject the opinion of those who
hold that crystals of leucite are pre-existent in the lava. The viscous
nature of these lavas prevented their being covered with fragmentary
scoriae, but caused the formation at first of a skin, which, thickening,
became at last a more or less pliable shell, that, when more solidified,
allowed the still fluid part to run as in a tube formed of this solid
shell. For many months the lava descended thus from the