236 "^he Philippine Journal of Science wis 



coralline limestone and clayey marl. The thick marl beds are 

 impervious and confine the water in the intervening porous 

 coral-reef members of the series. 



Coralline limestone is most abundant in the Visayan Islands, 

 especially in Cebu and Bohol. On both these islands it includes 

 marl beds, (iood wells have been obtained in this formation 

 in only about 50 per cent of the trials made. The chance of 

 encountering salt water is great if the well is drilled to a depth 

 which carries it much below sea level. In drilling through 

 coral, the hole should not advance far beyond the casing, even 

 though the wells may stand up well, and especial watch should 

 be maintained for impervious layers which may act as confining 

 agents. 



VOLCANIC BRECCIAS AND AGGLOMERATES 



Volcanic breccias and agglomerates, made up of varyingly 

 coarse and fine fragmental material embedded in tuff, are very 

 common in the Philippines. These rocks have usually been 

 deposited on the sea floor and, therefore, have been worked over 

 and roughly stratified by water, but heterogeneous breccias and 

 agglomerates of subaerial deposition are also known. These 

 rocks are found in the immediate vicinities of old volcanoes and 

 along lines of former volcanic activity. Much of the material 

 is indurated and impervious, but an equal proportion, perhaps, 

 is loose and porous. 



In massive breccias or agglomerates there is only slight chance 

 of obtaining artesian water, but where the fragmental material 

 has been deposited on a sea floor, and is, therefore, somewhat 

 bedded, artesian water may be obtained. Wells on the south- 

 eastern and eastern shores of Laguna de Bay have yielded 

 good flows from this class of rock. There is a considerable 

 area of bedded volcanic agglomerate around the base of Mount 

 Isarog in Camarines which ought to yield water, and likewise 

 in northern Camarines and in Sorsogon there are places at 

 which it is suspected rocks of this nature are water-bearing. 

 On the whole, however, volcanic breccias and agglomerates are 

 rather uncertain territory for the artesian-well driller. 



Mineralized water is often encountered in massive volcanic 

 agglomerate. Hot springs and other evidences of solfataric 

 action are associated with these rocks, so that in addition to 

 the possibility of encountering no water there is the further 

 chance that if water is encountered it may be too thoroughly 

 mineralized to be potable. 



