﻿116 BACON. 



great masses of steam and sulphur dioxide are continually rising from 

 its surface, so that it is only possible to see it when a favorable wind 

 blows the steam to one side; the water is covered with a greenish scum 

 which is continually broken by the bubbles of steam and gas rising 

 through it. The walls surrounding this crater lake are covered with an 

 efflorescent deposit which is white, red, yellow, blue, and green in color 

 and which is most probably not due to salts sublimed or distilled up on 

 the rock walls from the boiling, acid lake below, it being formed by the 

 action of the hot acid vapors on the lavas constituting the walls. That 

 this is the case is shown by the fact that the colors of this deposit are 

 stratified in a manner corresponding to the layers of lava. (See PL IV, 

 fig. 2.) Sublimation would not in all probability have given such a 

 stratification. This efflorescence consists of iron, aluminium and mag- 

 nesium sulphates and chlorides and just as is the case with the water, 

 aluminium is the predominant metal, iron coming next, and magnesium 

 being present in moderate amount. In many specimens of this efflores- 

 cence the acid radicals have been lost, so that the residue is largely 

 changed to hematites and clays. Oebbeke 2 in discussing the rocks from 

 Taal speaks of the large number of feldspars and other aluminous rocks 

 which he found in the neighborhood of the volcano, and gives the 

 following analysis of the massive rock from Taal volcano : 



Analysis of massive rock from Taal volcano according to Oebbeke. 



Si0 2 58.42 



A1 2 3 - 17.64 



Fe 2 3 - - 5.GC 



FeO 4.00 



MnO 48 



CaO 4.50 



MgO 2.54 



Na 2 4.44 



K 2 2.52 



H 2 42 



TiO, 31 



100.93 



Mr. W. D. Smith of the Division of Mines of this Bureau tells me 

 that he has examined rocks from Taal volcano and its immediate neighbor- 

 hood, which contained large amounts of many classes of feldspars. These 

 facts are mentioned as suggesting the source of the great quantity of 

 aluminium salts and of alumina noted in the waters and in the effer- 

 vescent deposits. 



From a chemical point of view the striking aspect of the volcano 

 consists in the large amount of salts of iron which are visible on all 

 sides; the rocks being to a great extent colored to a red or yellow owing 



2 Beitr. z. Petrographie der Philippinen u. der Palau-Inseln, Stutt. (1881), 27. 



