ing,
thus leaving four- and five-sided geometrical figures, all well fitting
in with their neighbours. Again, in this case, the lava, flowing over a
convex surface, had contracted on the surface and caused the wonderful
network of grooves. In one section the crater had the appearance of an
ancient Roman or Etruscan amphitheatre with seats in many tiers or steps,
separated by vertical cracks--as if cut out into separate blocks of
stone.

[Illustration: Strange Formation of Volcanic Rock.]

[Illustration: Volcanic Cavities (Matto Grosso).]

On the east side of the greatest portion of one crater--which would seem
to have been the most active of all--I found again immense boulders with
stratified rock above them resembling masonry work, just the same as and
at the same elevation as the layers I had examined in the larger
elongated horseshoe crater. In the centre of the smaller crater there
flowed a rivulet of crystal-like water most delicious to drink.
Undoubtedly those eastern rocks were the lip of the crater, for I
discovered there two flows of lava in corrugations and network designs
such as we had observed on the summit of the greater section. I had great
difficulty in climbing up the steep internal walls of the crater, and on
the steep slopes with dried grass, which was slippery to a degree. On the
top of the crater were great masses of carbonated rock; also patches of
lapilli, and red and white sand, plentiful everywhere in that zone.

The smaller crater--it seemed to me--must have been a mere safety valve
for the larger one. Its elevation, it will be noticed, was the same as
that of the latter. From the summit of the one on which I was standing I
could perceive the other to the E.N.E., forming the eastern boundary of
this immense volcanic hollow. The southern part of this great double
crater was subdivided into several sections, all in great rocky
terraces--quite vertical except in their lower portion, which was sloping
and had evidently been filled to a great extent by an accumulation of
ashes and erupted refuse. On the side on which I stood, however, the
crater had not the diabolical, quite awe-inspiring, appearance of the
larger section of the huge volcanic mouth--quite unscaleable by humans in
its central section. In the deep cracks in the rock were several small
grottoes. I experienced some difficulty and much fatigue in climbing to
the top (elev. 1,750 ft.) of the extinct volcano, and especially in
reaching