76 PRATT. 



level on the other. Whether or not this was the usual occurrence is not 

 certain, but judging from the positions of the two main fissures and 

 the fact that the displacement generally took place after the earth 

 stresses had apparently been relieved, this instance would be typical. 



If this system of fissures is along a plane of extensive former faulting, 

 as has been suggested, then earthquakes which affect southwestern Luzon, 

 independent of volcanic action, as well as those due directly to eruptions 

 from Taal, probably would be most violent along its trend. It would 

 mark both a volcano-tectonic and a seismo-tectonic line. The towns 

 of Lemery and Taal, situated as they are on this line, would especially 

 be menaced by earthquakes. As pointed out by Hobbs ^° in his study 

 of Italian earthquakes, the suggestion of mo^ang towns on such lines 

 should seriously be considered. 



Mud cones or craterlets. — Little violence, other than sharp earthquakes, 

 seems to have accompanied the formation of these fissures. jSTatives 

 say that a rash of gas occurred when the large one along the west side 

 of the Pancipit Valley opened. Several people noticed clouds of dust 

 shoot up along other fissures of the system. At Sinaysian, a harrio 

 near the seacoast on the large fissure just mentioned, a number of 

 gushing springs were noted soon after it opened. These springs are 

 not exactly on the fissure, but occur irregularly over a small marshy area 

 in the adjacent alluvial formation. On February 18, there were about 

 twenty still very active, gas escaping into the air with considerable noise, 

 and mud and water gushing up to a height of about one-half meter. 

 The loose ground around the larger vents was perceptibly agitated. Most 

 of the springs had built up mud cones, perfect craterlets of fragmental 

 tuff, perhaps 2 meters in diameter and 30 centimeters high. Both gas 

 and water were at ordinary temperature. 



Samples were taken and subsequently examined in the laboratory of 

 physical and inorganic chemistn^ of the Bureau of Science. The water 

 proved to be ordinary ground wat^r not unusual in any respect. It 

 probably bears no relation to the gas wliicli escapes with it, and is in- 

 teresting only as evidence of the disturbance of established ground-water 

 flow by the recent Assuring. 



The sample of gas showed 97 per cent carbon dioxide and a residue 

 of atmospheric air, probably from contamination in taking the sample. 

 The evolution of large volumes of carbon dioxide at this distance (18 

 kilometers) from the volcano is remarkable. Abella -^ visited the harrio 

 of Sinaysian in 1893 and examined the celebrated spring of San Ray- 

 mundo, which at that time had a flow of 151 meters per hour. He 

 observed the escape of gas near by. This spring has not fiowed for some 



^"Seismic Geol., Ibid (1907), 225. 



"Estudio descriptive de algunos Manantiales minerales de Filipinas. Inspec- 

 cion General de Minas de Filipinas, Manila (1893). 



