X, A, 5 Pratt: Reconnaissance in Caramoan Peninsula 309 



the dips vary in steepness up to the vertical and in direction 

 throughout the southern quadrants. There are at least three 

 limestone horizons in the sedimentary column, but because of the 

 complexity of the geologic structure, their exact position and 

 thickness are undetermined. The succession of beds as indi- 

 cated by the outcrops is contradictory in different localities, and 

 therefore the presence of faults as well as frequent reversals of 

 dip are suspected. 



At the base of the series is a compact limestone, usually red, 

 but also mottled gray at places. This limestone is very pure 

 in some exposures, but elsewhere contains considerable clay and 

 may even grade into calcareous shale. The lower limestone 

 member is lacking in some sections, and conglomerates, elastics, 

 and shale rest unconformably upon a basal formation of peri- 

 dotitic rocks and fragmental derivatives, thoroughly jointed and 

 metamorphosed. 



The shale-sandstone-conglomerate member of the sedimen- 

 tary column is not uniform in character. Exposures of black 

 calcareous shale in thin, perfectly defined beds were observed 

 in the river north of the town of Caramoan. Sandy yellow to 

 brown shales and massive tuff -sandstone outcrop on the upper 

 part of the same river southwest of Caramoan. It is here, also, 

 that the bed of coal occurs. The horizon is higher than that of 

 the thin-bedded shales to judge by the prevailing southwesterly 

 dip. At Guijalo on the southern coast, and evidently in the 

 base of the series, are fine conglomerates with rounded pebbles 

 of various rocks, including some quartz, shale with calcite lenses 

 between beds, and clastic or fragmental sandstones. The dip 

 is westward, and farther east, on the opposite side of Guijalo 

 Bay, a peridotitic basal complex is exposed, together with blocks 

 of the lower limestone. 



A gray, sandy limestone or calcareous sandstone, made up of 

 perfectly defined, thin, hard beds alternating with thicker and 

 softer layers, is included in the upper part of the sedimen- 

 tary series. The most extensive exposure of this limestone is in 

 the extreme southeastern part of the peninsula, where the beds 

 dip to the south-southwest at angles of from 30° to 40°. The 

 rock has been impregnated with silica, and the thin beds contain 

 numerous concretions of black and gray chert. The intervening 

 softer beds contain a considerable proportion of sharp frag- 

 ments of tuff. On the surface in this vicinity are numerous 

 pieces of iron-stained quartz, chalcedony, and silicified tuff. 

 Small lenses of tarnished pyrite occur in the softer, thicker beds ; 

 these were apparently mistaken for copper minerals during the 



