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above these lies a series which is more nearly horizontal, or to be exact, 
which has the same gradient as the stream itself. The streams, as eleva- 
tion continues, will be engorged in their old deltas, while they build new 
ones farther out to sea. 
MANANGA RIVER. 
The Mananga is typical and, as an example, will be discussed sepa- 
rately. A critical physiographic study of this river from its source in 
the Cordillera to the sea, is most instructive. It is selected because it is 
easily reached from the city of Cebu, and it presents nearly all the 
features of interest pertaining to the other streams of the island. 
Where it rises in the region of the Cordillera the declivity is at a 
maximum, and therefore the numerous tributaries are short, comparatively 
straight, and join the main stream at right angles. he latter is oriented 
north and south, because it follows the syncline in the limestone. In 
this part of its course it is a structural stream. Its valley is broad and 
shallow, in striking contrast to the conditions in its lower course. 
At the boundary between the older limestone and the igneous forma- 
tion, the stream swings sharply to the east and makes its tortuous way 
across to the younger limestone. In traversing the igneous formation it 
flows at the bottom of a deep and narrow cafion, winding back and forth 
to avoid the harder phases of the voleanic rock, which within short limits 
varies greatly in physical and chemical composition. In this portion of 
its course the Mananga would be called an antecedent stream—that is to 
say, it keeps the general direction it had when it was on the limestone 
which overlies the igneous rock. In the former part of its course it 
was a consequent stream, flowing to the east as a consequence of the 
slope of the formations. Having become well intrenched, it worked 
down to the basement rock or became superimposed upon it, without 
having its general direction changed. 
When the Mananga finally leaves the igneous rock it again becomes a 
consequent stream. In this lower portion its valley once more widens to 
a very broad, fertile, cove-like area, the valley of Jacupan. A_ local 
change in the character of the limestone formation, which being largely 
coral sand becomes very soft, and the occurrence of marl deposits account 
for this. | 
Still farther down we come to the gravel and sand plain near the 
sea, where the once vigorous and eroding stream is sluggish as it passes 
across old, dead, coral shelves finally to dip into the Mactan Sea. In no 
portion is the Mananga navigable even for bancas. In fact, this lack of 
depth is true of all the streams of the island, the condition principally 
being due to lack of sufficient feeding ground to support large streams, 
to limited plain country, and to the character of the rocks. The lack 
of certain classes of vegetation offers an added factor. ‘The absence of 
even one good, navigable stream connecting the coast with the interior 
produces a profound difference in the economy of the people. 
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