Vol. XI] DICKENSON— FAUNA OF THE VIGO CNOUP 3 



by Pratt and Smith to the Canguinsa formation and Vigo 

 group. In order that the reader may appreciate the significance 

 of this assemblage of mollusca, a brief resume of the geologic 

 history of this region is necessary. The southern half of the 

 Bondoc Peninsula consists almost entirely of marine sedi- 

 mentary rocks which have been highly folded and faulted. The 

 oldest rocks here recognized consist of shales and sandstones 

 3000 to 4000 feet in thickness, the Vigo group and its upper- 

 most member, the Canguinsa formation. The strata as ex- 

 posed in the vicinity of the Vigo River are steeply dipping, 

 black, organic shales, subordinate sandstones, and minor lig- 

 nitic strata which are unconformably overlain by the Malum- 

 bang formation.* 



The Malumbang formation, consisting of coralline limestone 

 and associated marls, varies in thickness from small residuals 

 to 1000 feet. From what is known of the rate of growth of 

 reef corals this formation must represent a long time interval. 

 In a few places in the Bondoc Peninsula — notably in the vicin- 

 ity of San Andreas — marine terraces truncate the Malumbang 

 strata. These terraces are in places thickly mantled with coral- 

 line limestone of Pleistocene age. Some of the limestone four 

 miles east of Mulanay at an elevation of 500 feet may represent 

 high Pleistocene terraces, as terraces at this height occur in 

 Leyte and at much greater elevations in Cebu where the same 

 geological horizons are also found. 



These horizons exhibit in northwest Leyte the same essential 

 conditions and are beautifully exemplified in the vicinity of 

 Toledo, Cebu, as well. The Vigo group in all probability 

 occurs in the region north of Fort Pickett in Mindanao so that 

 we are not dealing with local conditions but with general ones 

 which existed over the site of these islands. The conditions of 

 deposition during Malumbang and Pleistocene time resemble 

 those existing today in the vicinity of the Bondoc Peninsula 

 and essentially the same mollusca occur in the coral reef facies 

 of all three. The deposition during Vigo time was in marked 

 contrast with these later times in that the contributing land 

 masses consisted largely of diorites, schists, and serpentines or 



*Note. — The writer's view concerning the stratigraphy of this region differs in this 

 regard from that of Pratt and Smith, but a full discussion of this important point 

 «an not be made here. 



