The document discusses the geography of the Philippines. It describes the fertile Cagayan Valley located between mountain ranges in northern Luzon. It also details the Ilocos mountain range along the west coast of northern Luzon, which rises above 5,000 feet in places and is seldom below 3,500 feet, consisting largely of volcanic rock. The document also briefly mentions the rugged Zambales Mountains located in the southwestern part of northern Luzon.