1047 
walls. In some isolated portions there is still a capping of coralline 
limestone which gives a more or less even crest to the range, but where 
this is absent, as in the region of Mount Maupa (southwest of Cebu city, 
about 30 kilometers) the outline is serrated. 
The main folding in the island has taken place in an east-west direction, 
so that the axis of the folding runs north and south. The effect of this 
is to give the streams in the vicinity of the Cordillera a north and south 
direction. At their sources they may be east and west and the same may 
be true farther down, where they turn again to cut at right angles through 
the foothills. There is a minor cross folding north and south which 
somewhat modifies this arrangement of the drainage and which also 
causes the frequent sags in the high line of the central portions and a 
complete dying out of the ridge to the north. A reference to Abella’s 
geological sketch map of Cebu * will show that the courses of the streams 
on the various formations differ greatly. For instance, attention is 
called to the Cot-cot, the Baliguaguon, the Minanga, the Argao, ete. 
Rivers. After the discussion of the several physiographic regions, I shall 
take up in detail one of these rivers and treat its physiography from source 
to mouth. 
THE INTERMEDIATE UPLANDS, 
I have given this name to all the elevated region between the Cordillera 
and the coastal plains. It includes the more or less isolated ‘areas called 
mesetas by Abella. We might, with perfect justification, consider some 
parts of this large region as being made up of even two other physio- 
graphic divisions, but for the present paper we shall neglect such a 
separation. 
The surface rock is for the most part either limestone or marl, in some 
places sandstone or a coral sand formation. ‘The limestone varies from 
Miocene to post-Pliocene.® 
The geological events which have transpired to bring about the result- 
ing features of this upland country are many and have been quite 
* Burritt: The Coal Measures of the Philippines, Bull. Min. Bur. (1901), map 
p. 16, or accompanying Abella’s La Isla de Ceba. 
* One feature of the limestone is interesting and may be noted in passing. In 
an old, abandoned tunnel which was run in on the orbitoidal (i. e., Miocene) 
limestone, I found edible bird’s nests (Hirundo esculenta). Posewitz*® main- 
tains that stage y of the Pliocene may be inferred wherever these are found. It 
is true that the cave under consideration is not a natural one, although it ap- 
pears to be so, and these birds built their nests here in lieu of a more natural 
situation. If one relied on this criterion alone and considered this particular 
place he would very naturally call the limestone in question Pliocene. However, 
I can not believe that any geologist would trust to evidence like this for correla- 
tion. Doubtless all that is meant is that caves containing these nests are more 
abundant in the Pliocene. I coneur with Mr. Becker in calling this a most curious 
method of geological determination. 
° Posewitz, Theo.: Borneo, Berlin (1891), 190. 
