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Show 422 PLATEAU OF CAXAMARCA. from the autumnal tints which, in many of our forest trees, adorn the woods of the temperate zone at the season of the fall of the leaf. A single species of the South African family of Proteacere, Rhopala ferruginea, descends here from the cold heights of the Paramo de Yamoca to the hot plain of Chamaya. We often found here the Porlieria hygrometrica (belonging to the Zygophyllere ), which, by the closing of the leaflets of its finely pinnated foliage, foretells an impending change of weather, and especially the approach of rain, much better than any of the Mimosacere. It very rarely deceived us. We found at Chamaya rafts (balsas) in readiness to convey us to Tomependa, which we desired to visit for the purpose of determining the difference of longitude between Quito and the mouth of the Chinchipe (a determination of some importance to the geography of South America, on account of an old observation of La Condamine ).(1°) We slept as usual under the open sky on the sandy shore (Playa de Guayanchi) at the confluence of t.he Rio de Chamaya with the Amazons. The next day we embarked on the latter river, and descended it to the Cataracts and Narrows (Pongo, in the Quichua language, from puncu, door or gate) of Rentema, where rocks of coarse-grained sandstone (conglomerate) rise like towers, and form a rocky dam across the river. I measured a base line on the flat and sandy shore, and found that at Tomependa the afterwards mighty River of the Amazons is only a little above 1386 English feet across. In the celebrated River Narrow or Pongo of Manseritche, 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 ever 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. |