The surface of northern Luzon is made up of four distinct types.  First is the coastal plain —­ a consistently narrow strip of land, generally not over 3 or 4 miles wide.  The soil is sandy silt with a considerable admixture of vegetable matter.  In some places it is loose, and shifts readily before the winds; here and there are stretches of alluvial clay loam.  The sandy areas are often covered with coconut trees, and the alluvial deposits along the rivers frequently become beds of nipa palm as far back as tide water.  The plain areas are generally poorly watered except during the rainy season, having only the streams of the steep mountains passing through them.  These river beds are broad, “quicky,” impassable torrents in the rainy season, and are shallow or practically dry during half the year, with only a narrow, lazy thread flowing among the bowlders.

This plain area on the west coast is the undisputed dwelling place of the Christian Ilokano, occupying pueblos in Union, Ilokos Sur, and Ilokos Norte Provinces.  Almost nothing is known of the eastern coastal plain area.  It is believed to be extremely narrow, and has at least one pueblo, of Christianized Tagalog —­ the famous Palanan, the scene of Aguinaldo’s capture.

The second type of surface is the coastal hill area.  It extends from the coastal plain irregularly back to the mountains, and is thought to be much narrower on the eastern coast than on the western —­ in fact, it may be quite absent on the eastern.  It is the remains of a tilted plain sloping seaward from an altitude of about 1,000 feet to one of, say, 100 feet, and its hilly nature is due to erosion.  These hills are generally covered only with grasses; the sheltered moister places often produce rank growths of tall, coarse cogon grass.[5] The soil varies from dark clay loam through the sandy loams to quite extensive deposits of coarse gravel.  The level stretches in the hills on the west coast are generally in the possession of the Christian peoples, though here and there are small pueblos of the large Igorot group.  The Igorot in these pueblos are undergoing transformation, and quite generally wear clothing similar to that of the Ilokano.

The third type of surface is the mountain country —­ the “temperate zone of the Tropics”; it is the habitat of the Igorot.  From the western coastal hill area the mountains rise abruptly in parallel ranges lying in a general north and south direction, and they subside only in the foothills west of the great level bottom land bordering the Rio Grande de Cagayan.  The Cordillera Central is as fair and about as varied a mountain country as the tropic sun shines on.  It has mountains up which one may climb from tropic forest jungles into open, pine-forested parks, and up again into the dense tropic forest, with its drapery of vines, its varied hanging orchids, and its graceful, lilting fern trees.  It has mountains forested to the upper rim on one side with