ACROSS UNKNOWN SOUTH AMERICA 
Grosso plateau interested me greatly. Each individual 
spur, taken separately, showed slopes sometimes abrupt, 
sometimes well rounded, separated from the next spur of 
hills by a V-shaped or angular, or else a concave hollow. 
At the bottom of those hollows one did not find the slopes 
continuing the line of the crater, but the valley was there 
absolutely flat and cut the line of the slope sharply. It 
would almost appear as if a subsidence of the soil had 
taken place in that particular locality, or else one might 
speculate whether those abrupt hills had not once been 
the walls of a subterranean volcanic cauldron, the flat 
valley, in which we were, having been the bottom of that 
cauldron. What little rock one found in the river bed in 
this valley showed signs of having been exposed to intense 
and prolonged heat, and so did the brilliant red summit of 
the hill range, which was also of the deep red, typical of 
hard-baked rock. 
The scene which I had before me there in Matto 
Grosso greatly reminded me of a similar basin I had seen 
when the great Bandaisan mountain in Japan was blown 
up by a volcanic explosion and left merely the bottom 
part of its gigantic internal cauldron with vertical red 
walls around it. With the exception of scanty and ansemic 
grass and a few stunted trees, there was hardly any 
vegetation noticeable. The Fogasso stream, on the bank 
of which we camped, flowed in an easterly direction into 
the Araguaya. 
The temperature on the plateau was ideal: minimum 
63° Fahrenheit during the night; maximum 75°. We 
were at an elevation of 1,450 feet. 
On May fifteenth we were travelling through a valley 
over which must have once risen the continuation of a 
range which stood to the north of us. There were deep 
grooves and corrugations in the valley in a direction from 
south to north between the two sections of the now 
interrupted range. There we found soil of red, brown, 
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