The pyramids of the empire of the Incas are not less remarkable. There are at Saint Juan Teotihuacan, near lake Tezcuco, in the Mexican valley, two very large antique pyramids, which were consecrated by the ancient inhabitants to the Sun and Moon. The largest, called Tonatiuh Ytzalqual, or the House of the Sun, has a base of two hundred and eight metres, or six hundred and eighty-two English feet in length, and fifty-five metres or one hundred and eighty feet perpendicular elevation; being three feet higher than the great pyramid of Cholula. The other, called Meztu Ytzaqual, or House of the Moon, is thirty-six feet lower, and has a lesser base. These monuments, according to the first accounts, were erected by the most ancient tribes, and were the models of the Aztec Teocalli. The faces of these pyramids are within fifty-two seconds, exactly north and south and east and west. Their interior consists of massive clay and stone. This solid nucleus is covered by a kind of porous amygdaloid, called tetzontli. They are ascended by steps of hewn stone to their pinnacles, where tradition affirms, there were anciently statues covered with thin lamina of gold. And it was on these sublime heights, with the clear tropical skies of Mexico above them, that the Toltec magi lit the sacred fire upon their altars, offered up incense, and chanted hymns. One fact in connexion with these ancient structures is remarkable, on account of its illustrative character of the use of our small mounds. Around the base of these pyramids, there were found numerous smaller pyramids, or cones of scarcely nine or ten metres--twenty-nine to thirty feet elevation, which were dedicated to the STARS. These minor elevations, were generally arranged at right angles. They furnished also places of sepulture for their distinguished chiefs, and hence the avenue leading through them, was called Micoatl, or Road of the Dead. We have in this arrangement a hint of the object of the numerous small mounds, which generally surround the large mounds in the Mississippi valley--as may be witnessed in the remarkable group of La Trappe, in Illinois. A similar arrangement, indeed, prevails in the smaller series of the leading mound groups west of the Alleghanies. They may be called Star-mounds. If this theory be correct, we have not only a satisfactory explanation of the object of the smaller groups, which has heretofore puzzled inquirers; but the presence of such groups may be taken as an evidence of the wide spread worship of the Sun, at an early period in these latitudes.