TRANSACTIONS OF SECTION C- 671 



rents that admit large flows of sea-water to tlie lava, occasioning the formation 

 of vents and the greater explosive phenomena of eruptions. 



The formation of the actual surface volcano and the determination of its position 

 is therefore due to the sea, near which volcanoes are almost always situated. 



Emissions of lava without explosive effects are from volcanic tubes to which 

 large flows of water have not obtained admittance, and, on the other hand, purely 

 explosive eruptions, without lava-flows, are caused by water reaching lava which 

 fails to rise to the surface of the earth. 



The various forms of volcanoes the author considered could be explained by 

 these views, which opposed : — 



1. An infra-crust common centrjvl source of lava. 



2. The passage of lava through 30 miles of rocks, and consequeutlj- through any 

 greater thickness. 



3. The ejection of lava from its source by vertical pressure. 



4. The ejection of lava from its source by super-heated steam or ' potential 

 steam ' force. 



5. The passage of water through highly-heated rocks, either by fissures or by 

 capillary transmission. 



6. The accumulation or the presence of water at volcanic foci. 



7. A primogeneal ' water substance.' 



8. The importance of land surface water. 



The author had given much thought during many years to volcanology, and 

 had made personal observations of volcanic activity ; and whether his views were 

 approved or not he would be glad if they elicited facts and opinions that would 

 further a solution of the problem. He thought a discussion on the subject would 

 not be inappropriate at the city of Bath, famous as it was for thermal waters deriv- 

 ing their heat from what might be termed, according to his views, a volcanic focus, 

 but in this case one from which only benefit to mankind was received. 



Eighth Tieport on the Earthquake and Volcanic Phenomena of Ja-pan. 

 See Reports, p. 422. 



10. On the recent Volcanic Structure of the Azorean Archipelago. 



By OSBERT H. HOWAETH. 



The object of the author's notes upon the relation of the Azorean group to the 

 other islands of the West Atlantic is to indicate a line of inquiry by which some 

 approximation may be made to the intervals separating the great eruptive changes ; 

 and detennining any modifications in the type of flora during that important 

 succession of volcanic products which has been evolved since the Upper Miocene 

 period assigned to the islands generally. A field for such inquiry seems to be offered 

 by the present phase of action in the Furnas district, in the eastern centre of St. 

 Michael's, where existing activity is associated with some of the oldest formations 

 in the series. The author has traced in that valley a series of beds of vegetable 

 origin dating back from the most recent changes, immediately connected with the 

 present boiling-spring area, to a period antecedent to the formation of the Furnas 

 Valley itself. The intermediate intervals of repose are now represented by 

 peaty beds and subaqueous vegetable deposits, interstratified with the successive 

 lava streams, tuffs, and pumice-beds of various dates, within and prior to the 

 historical period. From the more recent of these, buried trunks and branches have 

 been obtained which represent the intervals of recent eruptions ; while in one of 

 the older tuft's, underlying nearly the whole series at that portion of the islands, a 

 tree (probably an Erica) has been found, presumably in situ, and offering possibili- 

 ties of a subjacent soil for examination, which would be contemporaneous with the 

 earliest vegetation of the island. 



11. Report of the Earth Tremor Committee. — See Reports, p. 522. 



