1SG0.] Account of a visit to Barren Island. 9 



large, but through many and smaller passages, distributed throughout 

 the thickness of the upper part of the cone. 



Second. — That some of these passages communicate with the loose 

 cover of ashes and stones which envelopes the rocky support of the 

 cone. 



Although I have mentioned some facts which seem to indicate the 

 existence of such favorable conditions, and which are moreover 

 strengthened by an observation by Captain Campbell, who saw vapour 

 issuing, and sulphur being deposited near a rocky shoulder about two- 

 thirds of the height on the eastern descent of the cone, still their 

 presence can only be ascertained satisfactorily by experimental dig- 

 ging. 



The Solfatara at Puzuoli, near Naples, is a similar instance of the 

 production of sulphur. It is a crater in which exhalations of watery 

 vapour, sulphurous acid and hydrochloric acid take place, and where 

 sulphur is also deposited. The sulphur is gained there by distilling 

 it out of the sand of the crater, to a depth of 10 metres or 32 feet 

 — it becomes too hot lower down — and returning the sand which af- 

 ter 25 or 30 years is again charged with sulphur. The permanency 

 of the volcano of Barren Island as a source of sulphur would depend 

 on the rapidity with which the sulphur would be replaced after the sand 

 had been once exhausted. The time required for this is not necessarily 

 fixed to periods of 25 or 30 years. In Iceland, at a similar spot, the 

 sulphur is renewed every two or three years. 



If a preliminary experiment should make it appear advantageous 

 to work the cone regularly, the material about the apex, after being 

 exhausted of the sulphur that is present, could by blasting and other 

 operations be disposed in such a way as to direct the jets of vapour 

 in the most convenient manner through uncharged portions of ground. 

 If the sulphur should aggregate in periods of not too long duration, 

 it would be possible to carry on the work of filling up new ground 

 on one side, and taking away saturated earth on the other at the same 

 time, so that after working round the whole circumference, the earth 

 that had been first put on would be ready to be taken away. 



If the periods should prove too long to allow the work permanently 

 to be carried on, an interval of time might be allowed to pass, before 

 resuming operations. 



c 



