Two miles or more away from the great edifices here mentioned, toward the west, is the “Castle of Mitla.” It was built on the summit of an isolated and precipitous hill of rock, which is accessible only on the east side. The whole leveled summit of this hill is inclosed by a solid wall of hewn stone twenty-one feet thick and eighteen feet high. This wall has salient and retiring angles, with curtains interposed. On the east side it is flanked by double walls. Within the inclosure are the remains of several small buildings. The field of these ruins was very large three hundred years ago. At that time it may have included this castle. AN ASTRONOMICAL MONUMENT. In this part of Mexico Captain Dupaix examined a peculiar ruin, of which he gave the following account: “Near the road from the village of Tlalmanalco to that called Mecamecan, about three miles east of the latter, there is an isolated granite rock, which was artificially formed into a kind of pyramid with six hewn steps facing the east. The summit of this structure is a platform, or horizontal plane, well adapted to observation of the stars on every side of the hemisphere. It is almost demonstrable that this very ancient monument was exclusively devoted to astronomical observations, for on the south side of the rock are sculptured several hieroglyphical figures having relation to astronomy. The most striking figure in the group is that of a man in profile, standing erect, and directing his view to the rising stars in the sky. He holds to his eye a tube or optical instrument. Below his feet is a frieze divided into six compartments, with as many celestial signs carved on its surface.” It has been already stated that finely-wrought “telescopic tubes” have been found among remains of the Mound-Builders. They were used, it seems, by the ancient people of Mexico and Central America, and they were known also in ancient Peru, where a silver figure of a man in the act of using such a tube has been discovered in one of the old tombs. RUINS FARTHER SOUTH.