716 ON THE VOLCANO OP TAAL, 



the most common substances emitted are two gases, sulphurous 

 acid and sulphuretted hydrogen. When these two gases come into 

 contact with one another, chemical action takes place, and the 

 elements contained in them — oxygen, hydrogen, and sulphur — 

 are free to group themselves together in an entirely new fashion ; 

 the consequence of this is that water and sulphuric acid (oil of 

 vitriol) are formed, and a certain quantity of sulphur is set free. 

 The water escapes into the atmosphere, the sulphuric acid combines 

 with lime, iron, or other substances contained in the surrounding 

 rocks, and the sulphur builds up crystals in any cavities which 

 may happen to exist in these rocks." — (Judd's Volcanoes, page 19.) 



Without propounding any new theory, there must be something 

 special in the nature of the underground rocks which causes them 

 to manifest themselves in the peculiar features of this crater. The 

 quantity of sulphur in it seems quite exceptionally great, as well 

 as the chlorides, and these are quite sufficient to account for the 

 large quantities of hydrochloric and sulphuric acid which are 

 found combined with the waters. 



There is another important question connected with the craters 

 of Taal, to which the Spanish geologist has given much careful 

 consideration. This is with regard to the former history of the 

 volcano, and to the theory which accounts for the lake of Bombon 

 by supposing that it occupies the site of a much larger volcanic 

 mountain which has been submerged. A short review of the 

 arguments relied upon is in every way worthy of attention. 



First of all Seiior Centeno points out the wide extension of the 

 ash deposits or tufas which seemed grouped around this volcano as 

 a centre, shows it to have been the principal focus of volcanic 

 activity in the southern part of the island of Luzon. The tufaceous 

 strata extend all round the lake to the sea, except on the eastern 

 side. Northward they entirely cover the strip of land between 

 the Laguna de Bay and the Bay of Manila. They also entirely 

 cover the country round the capital, and then are found extending 

 north as far as the town of San Ildefonso. This immense deposit 

 of volcanic cinders and dust v/hich is known to geologists as 



