between Santiago and San Borja, in a mountain ravine where at some points the overhanging rocks and the canopy of foliage forbid more than a very feeble light to penetrate, and where all the drift wood, consisting of a countless number of trunks of trees, is broken and dashed in pieces, the breadth of the stream is under 160 English feet. The rocks by which all these Pongos or Narrows are formed undergo many changes in the course of centuries. Thus a part of the rocks forming the Pongo de Rentema, spoken of above, had been broken up by a high flood a year before my journey; and there has even been preserved among the inhabitants, by tradition, a lively recollection of the precipitous fall of the then towering masses of rock along the whole of the Pongo,—an event which took place in the early part of the eighteenth century. 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 this remarkable occurrence. The powerful stream appears to be as 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 Marañon or Amazons. In order to pass from thence to the shores of the Pacific, the Andes have to be crossed at
