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Show PLATEAU OF C.A.XAMAitOA. 423 This fall, and the consequent blocking up of the channel, arrested the flow of the stream; and the inhabitants of the village of Puyaya, situated below the Pongo de Rentema, saw with alarm the wide river-bed entirely dry; but after a few hours the waters again forced their way. Earthquake movements are not supposed to have occasioned thi remarkable occurrence. The powerful stream appears to be, a it were, incessantly engaged in improving its bed; and some idea of the force which it exerts may be formed from the circumstance that, notwithstanding its breadth, it is sometimes so swollen as to rise more than 26 English feet in the course of twenty or thirty hours . . We remained for seventeen days in the hot valley of the Upper Maraiion or Amazons. In order to pass from thence to the shores of the Pacific, the Andes have to be crossed at the point where, bebetween Micuipampa and Caxamarca (in 6°57' S.lat. and 78°34' W. long. from Greenwich), they are intersected, according to my observation, by the magnetic equator. Ascending to a still higher elevation among the mountains, the celebrated silver mines of Chota are reached, and from thence with a few interruptions the route descends until the low grounds of Peru are gained; passing intermediately over the ancient Caxamarca, where 316 years ago the most sanguinary drama in the annals of the Spanish Conquista took place, and also over Aroma and Gangamarca. Here, as almost everywhere in the Chain of the Andes and in the Mexican Mountains, the most elevated parts are picturesquely marked by tower-like outbreaks of porphyry (often columnar), and trachyte. Masses of this kind give to the crest of the mountains sometimes a cliff-like and precipitous, and sometimes a dome-shaped character. They have here broken through calcareous rocks, which, both on this and on the northern side of the Equator, are largely developed; and which, according to Leopold von Buch's researches, belong to the cretaceous group. Between Guambos and Montan, 12,000 French (12, 790 English) feet above the sea, we found marine fossils ( 11) (Ammonites, nearly fifteen English inches in diameter, the large Pectan alatus, oyster shells, Echini, Isoca.rdias, and Exogyra polygona). A species of Oidaris, which, according to Leopold von Buch, cannot be distinguished from that which Brongniart found in the lower part of the |
