calcareous matter separated from the ore by partial decomposition. We may mention that the famous mine of Alpamina, wrought in the present day in this vicinity, is embedded in a matrix of limestone. Having descended some way from the cross on the highest point of the pass of Antacona, the surrounding rock (probably a variety of porphyry) has a reddish appearance, and is continued for a considerable distance to the village of Casapalca; and the soil also, at this part of the way, is of the same colour with the rock. We may likewise remark, that about the road-side, and in the river or mountain-stream, which is derived from the contribution of the numberless rivulets issuing from the heights, we see for the distance of about two leagues numerous large and small pudding-stones of the same reddish appearance. Casapalca, distant by common reckoning two long leagues from Tucto, is now considered as a village or pueblo, though it appears to have been originally merely a mining establishment. Here the attention is arrested by a pretty cascade, which, making a great perpendicular descent, is received into the interior of a jutting rock; and, after a subterranean passage of some extent, the concealed waters reappear, and in a gentle stream descend to join the river. From the foot of the Cordillera to Casapalca the llama thrives on the pasture, which it appears to find sweetest within a short distance of the snow-line. From Casapalca to the next village below it, called Pomacancha or Chicle, there are two leagues of good road; and here green barley may be sometimes had to feed the hungry cattle, that are often nearly famished by the time they have arrived this far, after having crossed the Cordillera. From Chicle to San Mateo, a distance of three leagues, there are two roads,—one by a famous steep or cuesta, and the other through a picturesque but rugged ravine along the windings of the river,—both of which we took notice of in describing the general features of the Sierra. San Mateo is a muleteer village like that of Obrajillo already described, and very much resembles it in climate and productions, though the temperature of the air may be a little colder here than at Obrajillo. In crossing by the high mountain-path from Chicle to San Mateo, we observed that where the ascent commences on the higher side, or that nearest the Cordillera, the rock at the base of the mountain consists of porphyry; but, as we ascend the great cuesta, the precipice assumes the character of porphyritic green-stone. At the base of the descent on the lower, or San Mateo side of the mountain, there is by the road-side a projection of rock which has the appearance of mica-slate, but of which none of our travellers took up a specimen; as by this time the day was far gone, and both men and cattle were fatigued, and anxious to reach the lodgings for the night in time to provide convenient accommodation.