Only two seasons are perceptible in the coast region of Peru, the winter months, from June to November, being cooler than those of summer, from December to May. Fogs are frequent between December and April, though they seldom last throughout the day. The heat is never intense, owing to the influence of the Humboldt current, which modifies the effect of the sun’s rays. Although apparently barren throughout a large extent of its territory, the coast zone is really rich in production and supports a large and flourishing population. In the subsoil of its arid plains, valuable deposits of petroleum have been found; its uninviting deserts contain saline beds of great commercial importance; and throughout its length appear at intervals beautiful and fertile valleys, watered by abundant streams and yielding enormous harvests of sugar-cane, cotton, rice, and all kinds of fruits. The rivers of the coast, though numerous, are of limited extent and volume, nearly all of them having their sources on the Pacific Slope of the Andes and flowing directly across the sandy strip of coast land to the ocean. During the summer, when abundant rains fall in the upper ravines of the Cordilleras, the coast streams carry plenty of water to irrigate the valleys; a few of them are navigable for a short distance, but only for small craft. The valleys drained by these rivers—about fifty in all—are like ribbons of green crossing the brown sands of the coast; their existence is an indication of the wealth which might be secured throughout the entire region by artificial irrigation. [Illustration: MONZON VALLEY, IN THE HUALLAGA REGION.]