﻿THE CRATER OP TAAL. 121 



direction depending upon the concentration of the alkali metal and metal 

 of the group of alkaline earths present in the solution. Nothing but 

 the high chlorine content suggests the sea as . a probable origin of the 

 waters of the crater lakes of Taal. The volcano is quite near the sea, but 

 the most eminent geologists incline to the view point that volcanic 

 waters do not usually come from that source. 9 



It seems most improbable, therefore, to judge from the composition of 

 the waters, that they originate in the sea, and it seems almost equally 

 improbable that the chlorine is due to sodium chloride without making 

 unproved assumptions, and consequently it is more rational to assume 

 that these waters have come from the original magma of the volcanic 

 core, for ferrous chloride occurs in meteorites, for example such as law- 

 rencite, 10 a mineral which is easily decomposed. 



THE RELATIVE ABUNDANCE OF THE CHEMICAL ELEMENTS. 



Clarke 1X says : 



The resemblance between meteoric stones and volcanic rocks is noteworthy. 

 * * * The earth below its crust may be like a huge meteorite in composition, 

 with the stony part predominating. 



He calculates as the average percentage amount in the earth's crust 

 of the principle elements mentioned here as follows : 



Chlorine 0.01 



Magnesium 2.08 



Iron 5. 40 



Sodium - : 2.30 



Aluminium 7.81 



Potassium 2.40 



Sulphur 03 



Calcium 3.77 



While the average amounts of chlorine and sulphur found in the earth's 

 crust are very small, still it is well known that various elements are 

 often concentrated in limited areas, as in the known eases of mineral 

 deposits. Hence the fact that so* small a percentage of chlorine and 

 sulphur are found in the earth's crust as a whole does not invalidate the 

 conclusion that these elements may have originated in the volcanic 

 magmas at this point. 



Van Hise makes the following statement : 



If at the time the earth stuff segregated, chlorine was contributed as 

 laurencite, it is certain that the action of waters in the magmas upon this com- 

 pound would produce hydrochloric acid; this suggests a source of a part of the 

 hydrochloric acid of volcanos. 



9 Chamberlin and Salisbury: Geology (1004) 1,572. 

 10 Van Hise: Metamorphism, 978. 

 n Bull IT. S. Geo. Sur. 78, 39. 



