1881.] Notes on the Earthquakes of July, 1880, at Manila. 461 



Philippine Government, in a work called " Memoria Geologico Minera 

 de los Islas Filipinas," observes : — " That the volcanic action in the 

 Philippine Archipelago is not displayed in an arbitrary or irregular 

 manner, but, on the contrary, is exercised by denned lines almost 

 parallel to each other, whose direction may be fixed as from N.N.W. to 

 S.S.Bi, thus showing two parallel systems, which to distinguish from 

 each other we will call the system of Taal, and that of Mayon, being 

 the names of the two volcanoes of the greatest and most frequent 

 activity in the two systems." 



The first, viz., the system of Taal, commences in the north of Luzon, 

 and after traversing the greater part of the island, including in its 

 course the active volcano of Taal, is lost in the sea of Mindoro, to 

 reappear in other islands of the Archipelago. 



The second system, "of Mayon," is situated to the eastward of the 

 first, and is represented by the magnificent active volcano of Mayon 

 of 8,000 feet altitude, and although parallel to the first, does not 

 extend farther to the north than the extinct volcano of Isero, in the 

 province of South Camerines, in Luzon, but traverses the southern 

 portion of the island, and includes the active volcano of Bulasan, at 

 the extreme southern point of Luzon ; it appears again in other 

 islands, especially in the large island of Mindanoa. 



Senor Centeno observes that these two distinctly parallel lines in 

 Luzon, with a distance of about 120 miles between them, after leaving 

 that island, approach each other so as to be only 64 miles apart in 

 Mindanoa, and in his opinion join each other in the southern group of 

 the Mollucas. 



The present earthquakes extended from Yigan, in the north, to 

 Tayabas in the south, being in the line of the system of Taal, which 

 volcano showed considerable and unusual activity during the dis- 

 turbance. The volcano of Mayon, oil the contrary, is reported as 

 being in its normal state, emitting no more than its usual amount of 

 smoke, although the volcano of Bulusan (in the system of Mayon, and 

 far to the southward of that mountain), which seldom shows signs of 

 activity, had recommenced to throw up smoke. This would appear to 

 corroborate Senor Centeno's theory, that the two systems are distinct 

 in Luzon, but join each other far to the southward ; and that the 

 effects of the earthquakes on volcanoes was confined to the system of 

 Taal on this occasion in Luzon, extending to the point where the two 

 systems united in the south, and penetrating on its return to the 

 north, along the system of Mayon, as far only as Bulusan, but not 

 reaching so far north as Mayon. 



The extent of these earthquakes is said to have been from Yigan to 

 Tayabas, a distance of about 220 nautical miles in length, with an 

 average width of about 75 miles. No shocks are reported from the 

 extreme north or south of Luzon. 



