250 The Philippine Journal of Science 1917 



inside and outside the crater. From certain points on the crater rim 

 sulphurous odors are noticeable, but none were detected in the bottom of 

 the crater. Steep precipitous walls formed the boundary of the crater on 

 all sides. At the foot of the walls, especially on the east side, large 

 quantities of ash and mud have been washed down and have accumulated. 

 The crater rim is highest on the south and north sides with altitudes of 

 304 and 230 meters, respectively. Nearly all of the west side is low, the 

 minimum elevation being about 95 meters. There are other low points 

 on the east side. 



The above description holds very well for the conditions in 

 the crater at the present time. There is a faint "sulphurous" 

 smell at various points, due to mineral decomposition, and there 

 are a number of small steam vents, principally on the north 

 crater wall and at the west shore of the lake. Most of these 

 vents were not readily accessible at the time the crater was 

 visited, but on the northwest shore there were some very small 

 openings, from which faint wisps of steam issued, and places 

 where the sand, under water, was hot to the touch. As evidence 

 of the insignificance of the present activity, it may be mentioned 

 that the temperature of the lake was about 30° C, which is only 

 a few degrees above that of ordinary surface waters in the 

 Luzon lowlands. 



There are also a few steam vents at various points on the outer 

 slope of the volcano, and there is at least one under water, on the 

 northern shore of the island. These, too, are insignificant. The 

 presence of steam vents under water has given rise to the belief 

 that there are hot springs at various points. So far as could be 

 determined, there is no foundation for this belief. 



Crystals of calcium sulphate, of iron salts, and of sulphur are 

 found on the walls and floor of the crater, the first being abun- 

 dant, the last very rare. Calcium sulphate is very plentiful, 

 especially near the shore of the crater lake, where it has ap- 

 parently been deposited from the water in large sheets a half 

 centimeter in thickness. 



Analyses of the waters of the crater previous to the 1911 

 eruption have been published by Centeno, in 1885,(4) and by 

 Bacon, in 1906(2) and 1907.(3) The analysis of a sample of 

 water from the stream flowing into the crater soon after the 

 eruption was published by Cox. (5) 



Bacon (4) made qualitative tests for radioactivity in the 

 waters and their sediments and found that the water and sedi- 

 ment from the old "green lake" were very feebly active, the 

 other waters and sediments showing no activity. Wright and 

 Heise(8) were unable to detect the presence of radium in the 

 water of the present crater lake. 



