From Santa Iñes the road continues gradually ascending to the little village of San Pedro Mama, where the two rivers, San Mateo and Santa Olaya, unite and form the Rimac. The walls of mountain which enclose the valley here rise almost perpendicularly, and afford nestling-places for small, richly-plumed parrots (Conurus rupicola, Tsch.). I was much surprised to see these birds inhabiting the barren rocks, as the parrot always dwells in woody regions, and is found in other places only when on its passage. I know no other species of this family, save the one I have just mentioned, which permanently nestles on mountains.
Three leagues beyond San Pedro lies the village of Cocachacra. It is a small and poor place, but is picturesquely situated, and enjoys a fine climate. Its name, signifying coca-field, or plantation, denotes that coca must formerly have been cultivated here. At present that plant is not grown in any part near the coast, as it requires a damp and very warm climate. Cocachacra is 5386 feet above the level of the sea. Maclean fixes the altitude of San Pedro Mama, Santa Olaya, and Cocachacra, at 5331 feet. Supposing this calculation to be correct with respect to the latter village, it cannot also apply to San Pedro Mama and Santa Olaya, which lie much lower. At the two last-mentioned places I made no barometrical observations.
On the Pasco road the hamlet of Llanga is situated, at twelve leagues from Lima. On the other road Cocachacra is the same distance from the capital; but Cocachacra is about 2400 feet higher than Llanga. Between Cavallero and Llanga there is an interesting geological phenomenon, which I will here describe.
At the distance of two leagues from Lima the road takes a turn. At first it runs direct north, or north-north-west; suddenly it turns to north-north-east, and advances along the bank of the river Chillon as far as Cavallero. From thence, with slight deviations, it continues in the same course to Llanga, but at a considerable distance from the river, as the latter takes a wide sweep northward. From Cavallero the road runs for the space of three leagues, still ascending, through a barren district, along the dry bed of a river, called the Rio Seco. The last half-league of the way is very steep, and leads to the ridge of a chain of hillocks running diagonally across the valley. The ground is strewed with fragments of porphyry and other kinds of rock, like the bed of the Rimac. On reaching the ridge of the line of hillocks, the traveller beholds on the other side a hollow basin, like the dry bed of a lake: a furrow, extending lengthwise through this hollow, is the continuation of the bed of the river which is intersected by the chain of hills. Descending into the valley, and again following the course of the Rio Seco to the distance of about three leagues, we reach the village of Alcocoto, and once more arrive on the bank of the Rio de Chillon.
Here, therefore, we have evidence of the following remarkable facts, viz.:—that at some former period the river of Chillon flowed north-westward from Alcocoto to Cavallero, in the bed that is now dry; and that a chain of hills has been upheaved diagonally across the valley and the river. By this chain of hills the water, being dammed up, formed a lake; then it was again driven back; until the stream broke into a new course at Alcocoto, by which means the lake emptied itself, and, having no new supply of water, it dried up. Now the Rio de Chillon flows from Alcocoto to Cavallero, taking a wide turn, first westward, next south-westward, and lastly, direct south, until, at a sharp angle, it unites with the old bed of the river. The point of junction is a quarter of a mile from the Hacienda Cavallero. This is, however, not a solitary example of the course of a river being interrupted by the uplifting of a ridge of hills. A similar instance is mentioned by Mr. Darwin, who, however, did not see it himself, but who describes it as follows, from the observation of his countryman, Mr. Gill, the engineer:—
"Travelling from Casma to Huaraz, not far distant from Lima, he (Mr. Gill) 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 water-course to indicate that the river had not flowed there a few years previously; in some parts, beds of sand and gravel were spread out; in others, the solid rock had been worn into a broad channel, which in one spot was about forty yards in breadth, and eight feet deep. It is self-evident that a person following up the course of a stream will always ascend at a greater or less inclination. Mr. Gill, therefore, was much astonished, when walking up the bed of this ancient river, to find himself suddenly going down hill. He imagined that the downward slope had a fall of about forty or fifty feet perpendicular. We here have unequivocal evidence that a ridge had been uplifted right across the old bed of the stream. From the moment the river-course was thus arched the water must necessarily have been thrown back, and a new channel formed. From that period, also, the neighboring plain must have lost its fertilizing stream, and become a desert."[55]
The inference here deduced is, that the rising took place at a period when the district was inhabited and cultivated by men. Of the period of the uplifting between Cavallero and Alcocoto I could discern no proofs. But the impression produced by the dry river bed involuntarily suggests the idea that, at no very distant period, it must have been the lodgment of a stream; for it is in all respects similar to the temporary dry river beds so frequently met with on the coast of Peru.
I made repeated visits to the Rio Seco, and I always contemplated with wonder the curious deviation of the river's course. But I must candidly confess that during my abode in Peru, I did not venture to attribute that deviation to so partial an uplifting; for I was ignorant of the existence of any similar phenomenon which would have supported such an opinion. Now, however, the example referred to by the eminent English geologist, and which has its existence on the same coast of Peru, sets all my doubts at rest, and I am quite convinced of the correctness of Mr. Darwin's view of the subject.
Having made this digression, I must now carry the reader back to Cocachacra. Pursuing the road to the distance of three leagues further, we arrive at San Geronimo de Surco. The valley in this part becomes more contracted; but on the whole its character is unchanged, with the exception that the mountains gradually become higher and steeper, and the soil less fertile. The road frequently runs along lofty walls of rock, or winds round sharp projections, which overhang deep chasms, in passing which the greatest precaution is requisite.
In several of the valleys on the road from the coast to the Sierra, and above all in the valley of Surco, there are certain springs, the water of which the Indians never drink. When a stranger unguardedly approaches one of these springs for the purpose of quenching his thirst, he is saluted by warning cries of Es agua de Veruga! (It is veruga water!) Even horses and mules are not suffered to refresh themselves at these springs, where the water is supposed to have the effect of producing a disorder called the Verugas. As the existence of this disease is not known in any other country, there appears ground for believing that it has its origin in certain local circumstances. The verugas first manifests itself by sore throat, pains in the bones, and other feverish symptoms. In the course of a few days an eruption of red-colored pimples, or boils, appears. These pimples sometimes increase in magnitude, till, in some parts of the body, they become nearly as large as an egg, and blood flows from them to such an excess, that the strength of the patient is exhausted, and consumption frequently follows. From the small verugas the flow of blood is greatest. I knew an instance of a half-caste Indian who from a small veruga below the ankle lost two pounds of blood.