X, A, 4 Pratt: Petroleum and Residual Bitumens 277 



mens, if not the petroleum, appear to be confined to regions 

 where dynamic action has been comparatively severe, resulting 

 in sharp folding, faulting, or intrusion. On the basis of this 

 observation the foregoing recommendation of the southern part 

 of the field is made. 



Where petroleum-bearing rocks are exposed at the surface, 

 as they are at I and J, shallow dug wells might be made to 

 yield a small quantity of petroleum. Initial production in Japan 

 and in Formosa came from dug wells. At any rate claim hold- 

 ers who lack capital for drilling might dig wells in this manner 

 to answer the requirements for assessment work. Similar ex- 

 cavations on outcrops of semiliquid bitumen like those at D 

 might also develop small flows of petroleum. 



In exploring the deposits of solid bitumens, hand drilling 

 should prove serviceable as supplementary to pits and tunnels. 

 Drilling alone would be unreliable in deposits of bitumen mixed 

 with clay-tuff like those at L and M. In tracing float bitumen 

 to the original vein or deposit in place, open trenching might 

 well be resorted to. Outcrops are obscure, and once a vein is 

 found, it should be followed closely by excavation. The presence 

 of faults may complicate the work of exploration. 



SUMMARY 



Several seepages of petroleum and a number of outcrops of 

 residual bitumens derived from petroleum occur in the region 

 of Villaba, Leyte, in easily accessible country. The containing 

 rocks are of Tertiary and Quarternary age. The principal 

 known occurrences are confined to an area 8 kilometers wide and 

 13 kilometers long. The petroleum appears to come from the 

 Vigo shale, which belongs to the lower Miocene or Oligocene, 

 while most of the residual bitumens are encountered in the Can- 

 guinsa clay-tuft", immediately overlying the Vigo. The various 

 formations can be correlated perfectly with the rocks in which 

 petroleum is found in Tayabas Province, and the two fields are 

 very similar. Petroleum is obtained commercially from the 

 same geologic horizon and from the same class of rocks in 

 Sumatra, Formosa, and Japan. The total thickness of the 

 bedded rocks is probably about 2,000 meters, and the petro- 

 leum comes to the surface at a horizon above the middle of the 

 rock series. 



The region of the outcrops and seepages in Leyte is sharply 

 folded, and the lower strata, including those which are petro- 

 leum-bearing, are intruded by small bodies of andesite, some of 

 which are domelike in shape. The distribution of the accumu- 



