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Show 412 PASSAGE OF CORDILLERA. April, 1835. effect on the atmospheric moisture, and therefore on the fertility of the valleys in the upper Cordillera. F~om the extreme slowness with which there is reason to believe the continent is rising, the longevity of man as a specie.s, required to allow of sufficient change, is the most vahd objection to the above speculations : for on the e~stern shores of this continent, we have seen that several ammals, belonging to the same class of mammalia with man, have passed away, while the change of level between Ian~ and water, in that part at least, has been so small, that 1t can scarcely have caused any sensible difference in the climate. I may add, however, that at Lima, the elevation, within the human epoch, certainly has amounted to between seventy and eighty feet. When at Lima, I conversed on this subject* 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 that condition, by neglect and subterranean movements injuring the water conduits, which the Indians formerly constructed on so wonderful a scale. I may here just mention that these people actually carried tunnels through hills of solid rock, when such were necessary to conduct the irrigating streams. M.r. 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 wonderful that any people should have attempted such operations without the aid of iron or of gunpowder ! * Temple, in his travels through upper Peru or Bolivia, in going from Potosi to Oruro, says, " I saw many Indian villages or dwellings in ruins, up even to the very tops of the mountains, attesting a former population where now all is desolate." He makes similar remarks in another place, but it is not possible to judge, whether this desolation is owing merely to a want of population, or to an altered condition of the land. April, 1835. OJOS DEL AGUA. 413 Mr. Gill mentioned to me a most interesting, and as far as I am aware, quite unparalleled case, of the effect of sub~ terranean disturbances in altering the drainage of a country. Travelling from Casma to Huaraz (not very far distant from Lima), he found a plain covered with ruins and marks of ancient cultivation, but now quite barren. Near it was the dry course of a considerable river, whence the water for irrigation had formerly been conducted. There was nothing in the appearance of the watercourse to indicate that the river had not flowed there a few years previously : in some parts beds of sand and gravel were scattered, and in others the solid rock had been worn into a broad channel.* It is selfevident that a person following up the course of a stream, will always ascend at a greater or less inclination. Mr. Gill was therefore very much astonished, when walking up the bed of this ancient river, to find himself suddenly going down hill. He imagined that the slope had a fall of about forty or fifty feet perpendicular. We here have the most unequivocal evidence, that a ridge or line of hills has been uplifted directly across the bed of a stream, which must have been flowing for many centuries. From the moment the river-course was thus arched, the water would necessarily be thrown back ; and a new channel would be formed on one side some way above. From that time, also, the neighbouring plain would lose its fertilizing stream, and become converted into the desert which it now remains. APRIL 5TH.-We had a long day's ride across the central ridge, from the Inca's bridge to the Ojos del Agua, which is situated near the lowest casucha on the western slope. These casuchas are little round towers, with steps outside to reach the floor, which is elevated some feet above the ground on account of the snow-drifts. They are eight in number; and under the Spanish government, were kept * Mr. Gill said he recollected that one part, which had been cut out of the solid rock, was about forty yards wide and eight feet deep. This is sufficient to give some idea of the size of the former stream. |