326 SMITH. 



their abundance: (1) Limestones; (2) shales and clays; (3) sandstones 

 and conglomerates; (4) tuff (waterlaid and subaerial) ; (5) cherts. 



Besides these there are numerous subaerial deposits, piedmont depos- 

 its, etc. 



1. Limestones. — These are for the most part coralline or foraminiferal. 

 They are quite pure chemically, the magnesia content being generally 

 less than Shper cent. They vary in color from cream- white through 

 buff to black. They have an extensive development, and vary in age 

 from Oligoeene to recent. 



According to the foraminifera they contain, Douville has recognized 

 three principal horizons, as has been shown by table 2. 



2. Shales and clays. — The former predominate in the coal measures, 

 varying in composition from clay to sandstone and usually are gray, but 

 in places may be buff and yellow. They make up many hundred feet 

 of thickness of strata in the Philippines. Their greatest development is 

 in the Visayan Islands, where the most extensive coal fields also occur. 



The clays vary in composition from very impure varieties high in iron 

 content to those which are practically pure kaolin. However, the latter 

 are very limited, in fact only small quantities have been found and these 

 in La Laguna Province. They are the result of the decomposition of the 

 feldspathic volcanic rocks of that region. 



The clays of the coal measures usually contain too much free silica 

 and not enough combined silica to be suitable for fire clay or cement 

 manufacture. 



3. Sandstones and conglomerates. — In the coal measures there are 

 several small seams which I call grit. Sometimes the quartz fragments 

 in this grit are over 2 centimeters in diameter. In addition there is at 

 least one thick stratum of a very impure, grayish sandstone overlying 

 the uppermost coal seams in some parts of the Islands, for instance in 

 Cebu. This formation more properly is called an arkose than a sand- 

 stone, because it contains more feldspathic, hornblendic, etc., material. 



The conglomerates are of two classes — basal, and those due to consol- 

 idation of gravel wash. 



The greatest development of conglomerate in the Islands known to me 

 is that bordering the igneous complex of north-central Luzon, as is seen 

 in sections along the Bued and Agno Elvers. Other great deposits of. 

 conglomerate are encountered farther north at an elevation of nearly 

 2,000 meters, but they are not basal. 



4. Tuffs. — There is a great deposit of pyroclastic material with inter- 

 calated beds of silt extending over a considerable area of southwestern 

 Luzon, particularly over Cavite and Batangas Provinces and the country 

 adjacent to Manila. A great deal of this material probably came from 

 Taal Volcano, but also from many other vents, many of which in a former 

 period existed throughout this region. When first quarried the deposit 



