this great valley; and then, by irrigation (which was formerly so well
understood by the Indians), the soil would easily be rendered
sufficiently productive to support a few families.
I have convincing proofs that this part of the continent of South
America has been elevated near the coast at least from 400 to 500, and
in some parts from 1000 to 1300 feet, since the epoch of existing
shells; and further inland the rise possibly may have been greater. As
the peculiarly arid character of the climate is evidently a consequence
of the height of the Cordillera, we may feel almost sure that before
the later elevations, the atmosphere could not have been so completely
drained of its moisture as it now is; and as the rise has been gradual,
so would have been the change in climate. On this notion of a change
of climate since the buildings were inhabited, the ruins must be of
extreme antiquity, but I do not think their preservation under the
Chilian climate any great difficulty. We must also admit on this
notion (and this perhaps is a greater difficulty) that man has
inhabited South America for an immensely long period, inasmuch as any
change of climate effected by the elevation of the land must have been
extremely gradual. At Valparaiso, within the last 220 years, the rise
has been somewhat less than 19 feet: at Lima a sea-beach has certainly
been upheaved from 80 to 90 feet, within the Indo-human period: but
such small elevations could have had little power in deflecting the
moisture-bringing atmospheric currents. Dr. Lund, however, found human
skeletons in the caves of Brazil, the appearance of which induced him
to believe that the Indian race has existed during a vast lapse of time
in South America.
When at Lima, I conversed on these subjects [3] with Mr. Gill, a civil
engineer, who had seen much of the interior country. He told me that a
conjecture of a change of climate had sometimes crossed his mind; but
that he thought that the greater portion of land, now incapable of
cultivation, but covered with Indian ruins, had been reduced to this
state by the water-conduits, which the Indians formerly constructed on
so wonderful a scale, having been injured by neglect and by
subterranean movements. I may here mention, that the Peruvians
actually carried their irrigating streams in tunnels through hills of
solid rock. Mr. Gill told me, he had been employed professionally to
examine one: he found the passage low, narrow, crooked, and not of
uniform breadth, but of very considerable length. Is it not most
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