Seven or eight miles more of very gradual downward slope brought us suddenly and unexpectedly to the brink of a magnificent canyon, the densely populated valley of Cotahuasi. The walls of the canyon were covered with innumerable terraces--thousands of them. It seemed at first glance as though every available spot in the canyon had been either terraced or allotted to some compact little village. One could count more than a score of towns, including Cotahuasi itself, its long main street outlined by whitewashed houses. As we zigzagged down into the canyon our road led us past hundreds of the artificial terraces and through little villages of thatched huts huddled together on spurs rescued from the all-embracing agriculture. After spending several weeks in a desert region, where only the narrow valley bottoms showed any signs of cultivation, it seemed marvelous to observe the extent to which terracing had been carried on the side of the Cotahuasi Valley. Although we were now in the zone of light annual rains, it was evident from the extraordinary irrigation system that agriculture here depends very largely on ability to bring water down from the great mountains in the interior. Most of the terraces and irrigation canals were built centuries ago, long before the discovery of America. No part of the ancient civilization of Peru has been more admired than the development of agriculture. Mr. Cook says that there is no part of the world in which more pains have been taken to raise crops where nature made it hard for them to be planted. In other countries, to be sure, we find reclamation projects, where irrigation canals serve to bring water long distances to be used on arid but fruitful soil. We also find great fertilizer factories turning out, according to proper chemical formula, the needed constituents to furnish impoverished soils with the necessary materials for plant growth. We find man overcoming many obstacles in the way of transportation, in order to reach great regions where nature has provided fertile fields and made it easy to raise life-giving crops. Nowhere outside of Peru, either in historic or prehistoric times, does one find farmers spending incredible amounts of labor in actually creating arable fields, besides bringing the water to irrigate them and the guano to fertilize them; yet that is what was done by the ancient highlanders of Peru. As they spread over a country in which the arable flat land was usually at so great an elevation as to be suitable for only the hardiest of root crops, like the white potato and the oca, they were driven to use narrow valley bottoms and steep, though fertile, slopes in order to raise the precious maize and many of the other temperate and tropical plants which they domesticated for food and medicinal purposes. They were constantly confronted by an extraordinary scarcity of soil. In the valley bottoms torrential rivers, meandering from side to side, were