From San Mateo to the next stage, or the village of San Juan de Matucana, the distance is four very long leagues, mostly through a narrow and rock-bound ravine. About a quarter of a league below San Mateo, green-stone rock discovers itself by the way-side; and, soon after we pass this crag, we cross the first of three bridges that are thrown over the river within the distance of little more than half a league between the first and last, on account of the narrowness of the ravine, that sometimes on the one side, sometimes on the other, hardly leaves space for a mule-road. Before crossing, in our descent, the first bridge, the rock is of limestone; but, on having at this place passed the water to the opposite side, the rock which presents itself is trap, and it continues nearly all the way from the first to the third or lowest bridge, where we meet with quartz, rising in very perpendicular and lofty masses. The rafters of the bridge rest on a projecting part of this towering cliff on the one side, and on the other on a corresponding projection of a formidable hill of porphyry opposed to it. The next variety of rock is one of trap formation; it appears about half-way between San Mateo and Matucana, and throws off a great quantity of fragments of a slaty appearance. On the lower side it is flanked by a hill of porphyritic green-stone, which continues to within half a league of Matucana. This mass also throws off an immense quantity of débris. The porphyritic green-stone is followed by trachyte porphyry, the rock of which commences a short way above the village of Matucana, or San Juan de Matucana; but, before the junction of these rocks takes place, the road-way is intersected by a wedge or angle composed of syenetic green-stone, or porphyry with actynolite. Having left Matucana (which is a considerable village enjoying a mild atmosphere, with some open ground around it,) for Surco, two or three leagues lower down, porphyry continues all the distance between these two villages. It throws off large fragments or masses, that nearly block up the road and bed of the river. Surco is a small village, which possesses the temperature of Yaso on the Canta road; and, like it, is notorious for its waters producing the disease called verrugas, or warty excrescences. From Surco to a league and a half, or thereabouts, below it, we have trachyte porphyry; and, as we ride along, it becomes gradually coarser-grained, till each grain at length appears as large as a hazel-nut. It is succeeded by felspar porphyry, which extends along the side of the ravine in which we travel to the extent of about two leagues and a half, or a league below the village called Cocachacra, situated three leagues lower down the river or ravine than Surco. Cocachacra, within twelve leagues of the capital, is surrounded by fruit-trees; and here the traveller may recline at his ease in the grateful shade, while refreshment may be procured for man and beast.