THE GEOLOGY OF LUZON, P.1. 41 
mountain sliding out, so that there is a great gap in the crater on 
one side. In spite of the great size of these mountains and the deep 
canyons on their slopes, they are of very recent origin. Recently 
Adams, who made a trip through that country, has compiled all of 
the various reports in a very interesting and able discussion in his 
“‘ Geological Reconnaissance of Southeastern Luzon,” which is found 
in Vol. VI, No. 6, Philippine Journal of Science. Of all the travelers 
through this district, Martin, the government photographer, is the 
only one who has brought back good photographic records. 
In 1909, Mr. Martin and a Franciscan Father from the town of 
Tobaco, made an ascent of Mount Mayon and secured fine pictures 
of the crater and of the country as seen from the crater. The most 
interesting point in connection with Mount Mayon, is, that the 
curve of its slope is so perfect that it can be represented by the 
formula for the sine curve: 
4 e~*/¢¢—x/¢ 
C 2 
when c=8.6 mm. 
This was worked out by Dr. G. F. Becker of the U.S. Geological 
Survey, who made a geological reconnaissance of that region in 1got. 
An extensive population is found at the foot of these mountains, 
but in the higher parts there are only a few Negritos. 
This district is one of the finest in the Islands, from a scenic 
point of view, as well as agriculturally, and occasionally, as in 1900, 
very spectacular eruptions take place from Mount Mayon. 
Further south in Sorsogon is another large dissected volcanic 
stock called Mount Bulusan. This is very much like Mount Isarog 
in general appearance. 
THE RIVERS 
There is a host of rivers of all sizes in Luzon. I shall, however, 
refer to eleven only. The largest river is the Cagayan in the 
northern part of the island, the shortest, perhaps, is the Pasig, but 
from a human standpoint, the Pasig is by far the most important 
of all. 
The Cagayan.—This river rises at about latitude 16°, and empties 
at Aparri, N. 18° 30’. Apart from local sinuosities it is a remark- 
ably straight river, leading one to believe that it must follow some 
