238 The Philippine Journal of Science mz 



Andesites and diorites are the predominant rocks in the Phil- 

 ippines. This will give an idea of the composition of the sedi- 

 ments, which, of course, have been derived- largely from the 

 erosion of these rocks. 



THE SEDIMENTARY SERIES 



The Philippine sedimentary formations consist of limestone, 

 sandstone, shales, conglomerates, volcanic tuffs, and cherts. 



This group includes the usual general classes to be found in 

 any part of the world. The following list shows the order of 

 their abundance : (1) shales and clays ; (2) limestones; (3) sand- 

 stones and conglomerates; (4) tuff (waterlaid and subaerial) ; 

 (5) cherts. 



Besides these there are numerous subaerial deposits, piedmont 

 deposits, etc. 



Shales and clays.* — The shales predominate in the coal meas- 

 ures, varying in composition and texture from almost clay to 

 sandstone and usually are gray, but in places they may be buff 

 and yellow. They make up many hundred meters of thickness 

 of strata in the Philippines. Their greatest development is in 

 the Visayan Islands, where the most extensive coal fields also 

 occur (Plate I). 



The clays vary in composition from very impure varieties 

 high in iron content to those which are practically pure kaolin. 

 However, the latter are limited. 



The clays of the coal measures usually contain too much free 

 silica and not enough combined silica to be suitable for cement 

 manufacture. 



Besides the shales of the coal measures there are thin beds 

 of shale intercalated in the great tuff series near Manila. I 

 have found a few plant remains in these shales, and these 

 indicate that this formation is comparatively recent. Surpris- 

 ingly few plant impressions have been found in the coal measures. 



Certain shale horizons show a great abundance of Foramini- 

 fera and other microscopic forms. On these I have done little 

 work. Karrer 5 has described 27 new species of these minute 

 organisms from the shales near Iba, Zambales, Luzon. These 

 comprise species in the following families : Uredillse, Milliolidae, 



4 No attempt is made here to describe these formations in detail as the 

 numerous geologic papers already published by this Bureau furnish these 

 data. 



s Karrer, Felix. Die Foraminiferen der Tertiaren Thone von Luzon, ap- 

 pendix to Fragmente zu einer Geologie der Insel Luzon, von Drasche, R. 

 Wien (1878). 



