18. 1 Dickerson: A Fauna of the Vigo Group 3 
group. In order that the reader may appreciate the significance 
of this assemblage of mollusca, a brief resumé of the geologic 
history of that region is necessary. The southern half of the 
Bondoc Peninsula consists almost entirely of marine sedimen- 
tary ro¢ks which have been highly folded and faulted. The 
oldest rocks here recognized consist of shales and sandstones 
from 3,000 to 4,000 feet in thickness, the Vigo group and its 
uppermost member, the Canguinsa formation. The strata as 
exposed in the vicinity of Vigo River are steeply dipping, black, 
organic shales, subordinate sandstones, and minor lignitic strata 
which are unconformably overlain by the Malumbang forma- 
tion. 
The Malumbang formation consisting of coralline limestone 
and associated marls varies in thickness from small residuals to 
1,000 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 vicinity 
of San Andres—marine terraces truncate the Malumbang strata. 
These terraces are in places thickly mantled with coralline lime- 
stone 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 geologic 
horizons are also found. These horizons exhibit the same es- 
Sential conditions in northwestern Leyte 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 Pikit 
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 resembled those existing to-day in the vicinity of the Bon- 
doc 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 peridotites from which they were probably 
derived. At times the material contained in the Vigo sandstones 
is very coarse, and conglomerates occur locally in the Bondoc 
Peninsula and on a great scale in northwestern Leyte, east of 
the Barrio of Tababunga, where they in part closely resemble 
“The writer’s view concerning the stratigraphy of the region under 
discussion differs in this regard from that of Pratt and Smith, but a full 
exposition of this important point can not be given here. 
