Only a hint of greatness, but when, standing beside the ruins, the boys looked over the country below them, the real magnitude of the work became apparent. Following the pointing forefinger of the elder man, Roger could see what ninety-nine out of every hundred would have overlooked, the regular relations of green defiles, which, though veiled by the hand of time, were evidently artificial work. One great canal could be traced tapping the Salt River on the south side, near the mouth of the Verde; this, for three miles and a half, formerly flowed through a bed cut by hand out of the naked rock in the Superstition Mountains to a depth of a hundred feet. This canal alone, with its four branches and the distributing ditches, irrigated 1,600 square miles of country, and the engineering would be no disgrace to modern times. "And how long ago were these canals dug?" asked Roger. "No one knows," was the truthful and unhesitating reply. "It is a puzzle that so far archæologists have tried in vain to solve. They must be older than the Aztlan civilizations----" "What are those?" asked Phil. "Aztecs, Toltecs, and that bunch, aren't they?" queried Roger, wanting to show his knowledge. "Mayas, too," said the other, smiling assent, "and they must be older than the Nahoa empire, of which little is left except in the south of Peru. Just how old is impossible to say, and the only clew we have is that these canals and ditches are in part filled up with volcanic lava and debris from the Bradshaw mountains, and geologists are able to show that these eruptions cannot have taken place less than two thousand years ago." "That's as old as Rome!" said Roger in surprise. "That means that the end of it, at latest guess, was older than the beginning of Rome, practically. And, though this volcanic action has been later than these immense works of early man in America, there is left neither a tradition of the millions of people who lived then, nor even of the forces which led to the decay of the empire and the overwhelming volcanic disaster in which it may have closed." On their way back to the train, the old traveler gave Roger a long account of the early settlement of that part of the country by the Spaniards, and pointed out, as they passed through Tucson a few hours later, the quaint mediæval architecture of a town which claims its beginning as far back as 1560, and in which many houses three centuries old are still standing; the oldest town in the Southwest, with the exception of Santa Fé. A mirage, or rather a succession of them, formed the basis for some thrilling African desert tales, with which Phil's father was well-primed, and when, passing round the mile-long horseshoe curve, the train pulled into El Paso, Roger was extremely sorry to leave the friends who had made his trip such a pleasant one.