26 The Philippine Journal of Science 1922 
the field in the neighborhood of the Babuy Mountains is exceed- 
ingly rugged, with elevations up to 1,000 meters. The eastern 
part of the field is not so high, but owing to the limestone 
formation generally occurring in that portion the ground is 
exceedingly rough, and deep gorges are the rule. The center 
of the field is moderately level and open grassland in the vicinity 
of Malitabug River. Along Malitabug River are some very 
conspicuous terraces; three of these are prominently developed 
and two others are not so well defined. In the southern part of 
the field, just north of Fort Pikit, there is a great number of 
low hills, in part wooded and in part grass covered. Some of 
these hills are rounded and are made up of shales and sandstones, 
but many others are composed entirely of coral limestone and 
are generally flat topped. The hill on which Fort Pikit is 
located is typical of many of these hills (Plate 2, fig. 2). This 
is a raised coral reef of late Pleistocene or early Recent time. 
These outliers on the average stand about 50 meters above the 
Rio Grande. To the east of them lies the vast fiat-bottomed 
valley of the Rio Grande. 
After one has made a short study of this region, it is fairly 
easy to determine from a distance the general type of rocks 
underlying the different kinds of topography. For example, 
shale and sandstone are usually indicated by rolling, grass- 
covered hills; igneous rocks are found in the high, rugged, 
partially wooded mountains; the limestone areas are interme- 
diate in elevation, usually with steep slopes and escarpments, 
and generally densely wooded. Traveling in the limestone areas 
is most difficult, owing to the considerable amount of solution- 
yielding caverns and sinks. 
There is no accurate topographic map of this region availa- 
ble. An approximation to the topography indicated by hachures 
is found in the map issued by the Philippine Constabulary. The 
writer has seen a contour map of a portion of Cotabato Province, 
made some years ago by the topographers of the United States 
Army, but this map is not for general use. It is also known that 
private companies recently making investigations in this field 
have made topographic maps of a portion of this country; 
these also are not available to the public. The best way to 
map this country would be by photography from aéroplanes 
or by triangulation and plane-table sketching. The use of 
transit and steel tape is not necessary, as the preliminary geolog- 
ical work in this region does not call for such accuracy nor for 
