Alfred Russel Wallace : Alfred Wallace
: A. R. Wallace :
Russel Wallace : Alfred Russell Wallace
Comments on the Physiography of the
Upper Amazon Region (S128: 1867)
Editor Charles H. Smith's Note: Comments offered in discussion of
a paper on a tributary of the Rio Purus in Peru, delivered by Mr. W. Chandless
at the 25 February 1867 meeting of the Royal Geographical Society. These
comments later printed in Volume 11 of the Society's Proceedings
series. Original pagination indicated within double brackets. To link
directly to this page, connect with: http://people.wku.edu/charles.smith/wallace/S128.htm
108]] Mr. Wallace, in answer to an invitation by the President,
said he had not himself visited the interesting district described in
Mr. Chandless' paper. There appeared, however, to be a very singular geographical
fact brought out by the discoveries of Mr. Chandless, namely, a very great
similarity or parallelism between the tributary rivers on the south of
the Amazons and those on the north--particularly between the Purus and
the river Uaupés, an [[p. 109]] affluent
of the Rio Negro, which he (Mr. Wallace) ascended. It was a very curious
circumstance that an immense district of country immediately at the foot
of the Andes, both north and south, should, apparently, not receive a
single drop of water from those mountains. On the south of the Amazons
there was an enormous triangular district, as large as France, between
the Madeira and the Ucayali, and immediately below the great range of
the Andes, and yet its rivers were not derived from that range. Exactly
in the same manner, on the north of the Amazons, the Japura and the rivers
east of it appeared to terminate in the great forest-plains before they
reached the Andes. He had ascended the Uaupés far enough to ascertain
the same fact with regard to this stream. Though prevented from reaching
its source, he ascended to a point near a cataract, where the river, though
very wide, was a slow, sluggish, black-water stream, and he heard that
for 10 days' journey farther up it continued so all the year round. This
was a sufficient proof that not a drop of water came from the slopes of
the Andes. Hence, there were enormous plains north and south of the Amazons
which were, by some means, cut off from the drainage of the Andes. It
would be very interesting to ascertain what was the cause of this separation.
It would appear probable that it must depend in some manner upon the peculiar
contour of the country. There might be a local elevation or ridge near
the foot of the range, but separated from it, which caused the water to
flow north and south and find an outlet in one of the great rivers. He
observed in the map figures indicating the altitude of the river Purus
at different points. He wished to ask Mr. Chandless whether those figures
could be relied on?
Mr. Chandless, in reply, said that he believed,
quoting from memory from Mr. Wallace's book, that it was found that the
barometer stood higher at the town of Barra than at Pará, and he
had found that at 600 miles up the Purus it stood higher than at Barra.
That, of course, gave a false result as to elevation, but he believed
that the observations were quite correct instrumentally. His barometer
had been tested at Kew. Some allowance must be made for receding from
the equator and the diminution of the equatorial depression of the barometer.
He could not believe that at a point 1500 miles from the sea the elevation
would be only 107 feet . . .
Mr. Wallace asked whether Mr. Chandless had any simultaneous observations
made at Barra while he was on the Purus.
Mr. Chandless replied that he had not.
He had given, besides the means of his barometrical observations, the
assumed means at the sea-level, but could not say whether these were correct
. . .
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