226 The Philippine Journal of Science 1913 



Two originated along line H — H; and the third, in the eastern 

 part of Laguna Province, along line D — D. 



The earthquakes of July 25, 1880 (5, 8, 9), show that the des- 

 tructive area conforms pretty closely to that shown in chart VII. 

 These should both be classed as tectonic. 



Earthquakes of May 15 (4, 5, 6, 8) and of July 11, 1881 

 (15) . In the case of the former, the destructive area is confined 

 to the Eastern Cordillera in north-central Luzon, and is clearly 

 of tectonic origin. That of the latter had its center on the 

 Island of Guimaras, just south of Panay. This is clearly of 

 tectonic origin, and it was probably due to displacements along 

 the contact between the Tertiary sediments of the western half 

 of the island and the igneous rocks of the eastern half. 



The earthquake of July 16 in Ilocos Norte Province, Luzon 

 (2), was undoubtedly due to disturbances along the line A — A. 



Earthquakes of September 10, 1881 (5) . The area of destruc- 

 tion during these earthquakes was very local, being in the south- 

 ern part of Nueva Vizcaya, and may be attributed to purely 

 local causes, possibly rockfall. 



The earthquake of September 30, 1881 (4, 5), again centers 

 in Nueva Vizcaya, and was probably of the same origin as the 

 previous one. 



Earthquake of April 30, 1882 (7, 8) . The destructive area 

 was very local and was centered just north of Manila Bay, but 

 more to the westward near the contact between the material 

 of the valley floor and the volcanic rocks of the Zambales 

 Mountains, hence there seems to be some reason for conjecturing 

 that it is due to tectonic causes. On September 12, a very 

 similar earthquake occurred in the same region. 



Earthquakes of July 25 (7, 8) and 28 (2), 1882. During the 

 former, the epicentral area is situated between Taal Volcano 

 and the China Sea, and hence may be of volcanic origin. That 

 of July 28 is located along the Cordillera of Luzon in the 

 northern part, and hence may be called tectonic. 



The earthquake of September 11, 1882 (7), has its focus 

 somewhere near Taal Volcano. 



Two earthquakes on September 17 (10) and 21 (2, 3), 1882. 

 In the case of the former, the destructive area is centered about 

 the southeastern volcanic cluster in Luzon. The latter has its 

 epicenter in north-central Luzon, but the longitudinal axis of 

 the destructive area runs slightly north of east. We do not 

 know of any prominent structural line in that region running 

 in that direction. The course of the Abra River, where it makes 

 a sharp right-angled bend to the west in the latitude of Vigan, 



