or At 
WOODWORTH: GEOLOGICAL EXPEDITION TO BRAZIL AND CHILE. 21 
to a deep brown earthy mass, and in small patches I saw reddish, and 
in one place, greenish clay. Bales of spherical separation appeared 
here and there and often the road led the mules between large angular 
blocks which bestrewed the hard trappean surface. The contrast 
between this thin coat of weathered trap and the deep beds of de- 
composition forming the terra rora in Sao Paulo is very striking. 
The Brazilian pine, Araucaria, occurred in small patches here and 
there and many young plants pointed to favorable conditions of growth 
for the species. An occasional Maté tree appeared along the trail, 
evidently due to the droppings from some passing caravan. [rom 
this high plateau there was a good view of a high trap range of tabu- 
lar outline in the distant northwest, the prolongation of the Serra do 
Espigao extending towards Porto da Uniaéo. The wooded surface 
of the range concealed all the rocks, but the triple terraces of the mass 
presumably signify a three-fold division of the trap sheets of which it is 
composed. Between our position at Corisco and this tabular moun- 
tain there lay an extended lower surface, the deeply dissected basin 
of the Rio Correntes. 
Along the mule path, we passed several small grassy pools, occupy- 
ing depressions partly enclosed in the trap. In at least one instance a 
pool lay on the upper side of the road and the water was held in by a 
barrier of mud and gravel accumulated in the road by wash from the 
descending grade on either side to the sag by which the drainage 
normally overflowed. The surrounding gramineous plants displayed 
the brown color of winter. The fine green grass of one of the pools 
had attracted to it a domestic horse which stood up to his knees 
feeding, evidence that the bottom was floored with probably the same 
stiff residual clay which later I saw in an excavation in one of these 
basins. On this monotonous succession of trap uplands of nearly 
uniform structure the trivial relations of the life which found a place 
upon them became matters of more than passing interest. On the 
muddy bottom of the rivulet which flowed past the evening camp I 
found a small fresh-water mussel resembling Unio crawling along 
with the open edges of the valve down so as to leave a deep narrow 
groove in the mud. ‘The trail was sinuous and ended in a burrow 
where the molluse pushed under a cover of mud. I should have 
assumed, had I not seen this animal at work, that the trail, as have 
been so many found in the fossil state, was to be ascribed to some 
gasteropod. 
August 23rd.— The morning broke cloudy with rain threatening, 
for in this latitude on the trap plateau the distinction between a dry 
