VOLCANIC COUNTRY 
impair the drum of one’s ear. The result was truly 
marvellous. Brass instruments were preferred by the 
Indians. The trombone was the most loved of all. As 
the Indians all possessed powerful lungs, they were well 
suited to play wind instruments. 
The colony was situated in one of the most 
picturesque spots of Matto Grosso. When out for a 
walk, I came upon a great natural wall of rock with 
immense spurs of lava, the surface of which was cut up 
into regular geometrical patterns, squares, and lozenges. 
I think that in that particular case the peculiarity was due 
to the lava having flowed over curved surfaces. On 
coming in contact with the atmosphere, it had cooled more 
rapidly on the upper face than the under, and in contract¬ 
ing quickly had split at regular intervals, thus forming 
the geometrical pattern. 
We were undoubtedly in the former centre of incon¬ 
ceivable volcanic activity. In other parts of a great dome 
of rock I came upon strange holes in the rock, extremely 
common all over that region, which might at first glance 
be mistaken for depressions formed by glacial action, 
but which were not. They were merely moulds of 
highly ferruginous rock, granular on its surface and not 
smoothed, as one would expect in the walls of cavities 
made by the friction of revolving ice and rock. Nor 
did I ever find at the bottom of any of those pits, 
worn-down, smooth, spherical, or spheroid rocks, such as 
are usually found in pits of glacial formation. Those pits 
had been formed by lava and molten iron flowing around 
easily crumbled blocks of rock, or perhaps by large balls 
of erupted mud which had dropped on molten lava, that 
had then solidified round them, while the mud or soft 
rock had subsequently been dissolved by rain, leaving the 
mould intact. The latter theory would seem to me the 
more plausible, as many of those pits showed much 
indented, raised edges, as if splashing had taken place 
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