Tectonic Geography of Eastern Asia. — Hobbs. 377 
cipal tectonic lines of the archipehgo as they have been made 
out by Koto, have been indicated in figure i. 
Eecker'% after a careful review of the literature, expresses 
the opinion that too much effort has been made to show un- 
broken continuity of the volcanic zones in the archipelago, and 
adds: 
"Fissures occur far more often in parallel systems than singly, and 
just as dikes frequently jump from one fissure of such a system to 
another, so, I think, do the greater volcanic phenomena. Fissures, 
furthermore, commonly occur in two systems, cutting one another at 
a large angl'^, and there are somewhat clear indications that such is 
the case wit^: the volcanic belts in the Philippines south of Manila. 
These two systems are approximately parallel to the two prongs of 
Masbate, but each is curved, the centers of curvature lying in the 
China sea, one of them much to the southward of the other. I should 
consider, provisionally, that the elevations of northwesterly trend, such 
as the mountains of eastern Mindanao, Leyte, Tayabas, Mindoro, 
northwestern Panay, and perhaps the northern extremity of Palawan, 
belong to the one system, but represent a considerable number of dif- 
ferent though associated fissures. The trends of the northeasterly 
character also seem to belong to one system. The western fork of 
Masbate appears to continue to northeastern Panay, but to be inter- 
rupted with an offset in the southwestern portion of that island. The 
southerly prolongation, it seems to me, is to be found in the Cagayanes. 
Of course Palawan, Negros, excepting the southern end, and the Bas- 
ilian-Jolo group belong to this system. So nearly as I can make out 
by plotting, the two systems intersect at pretty constant angles of about 
60°. A fairly consistent and satisfactory scheme of short arcs can be 
arranged in this way for the ranges south of Manila, but I hesitate to 
print my diagram, because a map conveys an impression of certainty 
and definiteness which in this case would be erroneous, f 
■'To the northward of Manila the same scheme of ranges seems less 
plausible. I zm almost inclined to think that the Sierra Madre and the 
Caraballo del Norte, which are composed largely of crystalline schists, 
are each made up of short arcs belonging to each system. Some 
support for this guess is to be found in Mr. d'Almonte's large map 
of Luzon, where the watersheds show several zigzags. This region is 
perhaps a 'horst' in Mr. Suess's sense. As for the Sierra Zambales, it 
seems to me most probable that it continues southward through Pico 
de Loro and cape Santiago to the lofty Alcon peak, in Mindoro, and 
so into Mariveles through Pico de Loro to Balayan, near cape Santi- 
ago, in Batangas province. The western range of middle Luzon would 
• I. c, pp. 545. 
t Dana called attention to the symmetry exhibited in the trends of the 
islands. "Thns the body of Luzon is at right ancles with the southern extrem- 
ity; Palawan is at right angles nearly with Mindoro," etc. He also points out 
that both of the two systems of trends are curved. 
