﻿THE CRATER OF TAAL. 123 



radium content. Since the first paper was published, Major Dutton 13 

 has advocated a theory that there is a causal connection between radio- 

 activity and volcanos. A volcano is located in a part of the earth where, 

 for some reason, radium compounds are concentrated, and he believes 

 that the radium salts are the ultimate source of the volcano's heat 

 supply. His arguments in favor of this theory are briefly as follows : 



1. The solidity of the earth does not exactly correspond with other theories. 



2. The comparative smallness of the extravasated masses in any single eruption 

 is in favor of his view. 



3. The repetitive nature of volcanic eruptions favors his contention. Why 

 does not a volcano discharge all the material in one stupendous helch, and then 

 close forever? 



4. There is a growing mass of strong and highly concordant evidence showing 

 that the seat of the reservoir is very shallow, it seldom being more than three 

 miles in depth; the indications being that most of the volcanic eruptions originate 

 at depths of between one to two and one-half miles. The evidence of this fact 

 is furnished by the earthquakes which almost always accompany such eruptions. 



We may now proceed to state the probable cause of volcanic eruptions. They 

 are caused I conceive by a development of heat, resulting from radio-activity in 

 limited tracts at a depth of 1 to 3 — at the very utmost not over 4 — miles from 

 the surface, which is sometimes sufficient to melt the rocks affected by it. The 

 melting is gradual, and when a sufficient quantity is melted, the water which it 

 contains becomes explosive and usually suffices to break through the covering, 

 constituting an eruption. When all the lava is erupted and the reservoir is 

 exhausted it closes up for a time. If the heat continues to be generated, more 

 lava is melted, and in due time another eruption occurs. The process may be 

 repeated again. It may be repeated hundreds or thousands of times. The volcanic 

 action may continue in the same place for hundreds of thousands or even millions, 

 of years, or it may repeat itself only a few times, or may even occur only once. 



Rausch von Trauenburg " made some observations on the crater of Vesuvius — 

 the gases from which produced marked ionization and a prompt discharge of 

 the leaves of the electroscope. 



Loudebeck 15 has answered Major Dutton in so far as the geologic phases of 

 the question are concerned. He shows that the composition of lavas is such as 

 to preclude their having their origin at such slight depths in the earth, for 

 they differ in chemical composition from the major sedimentary rocks, and hence 

 must have originated below the zone of sedimentation. 



If a volcano is such a center of radio-activity, a place where radium 

 is so concentrated in the earth's crust that the rocks are melted by the 

 perpetual heat store, then materials collected from a volcanic crater 

 should be exceedingly active. Taal, which is an active crater, offers a 

 good opportunity to test the theory. I have examined the waters col- 

 lected by this expedition as well as the. lavas, efflorescence and sediments. 

 The apparatus used was like that described in the former paper, being 

 an electroscope in a large chamber of the general type of instrument used 



"Joum. of Geol. (1906), 14, 259. 



"Quoted by Dutton, loc. tit. Castovina (Boll. Accad. Gioenia di 8c. ruit. 

 Catania (1900) 84, found rocks from Aetna slightly radio-active, the lavas the 

 least so, the soil from the mountain slopes much more active. 



15 Joum. of Geol. (1900), 14, 747. 



