THE 



GEOLOGICAL MAGAZINE 



NEW SERIES. DECADE VI. VOL. IV. 



No. XII.— DECEMBER, 1917. 



ORIG-IITAL AETICLBS. 



I. — The Ambrym Eruption's of 1913-14. 1 



By Professor J. W. Gregory, D.Sc, F.E.S. 



(WITH A MAP, PLATE XXXIII.) 



1. The Constituents of the New Hebrides. 



2. The Volcanic History of Ambrym to 1894. 



3. The 1894 Eruption. 



4. The Features of the 1913 Eruption — 



(a) The Explosion Trough. 



(b) The Lava Pipes. 



(c) The Fissure Eruptions. 



5. The Eocks of the 1913 Eruption. 



6. General Eelations of the Ambrym Eruptions. 



7. Eeferences. 



1. The Constituents of the New Hebrides. 



(HHE rocks of the New Hebrides belong to at least four groups — 

 J_ two series of limestones and two series of volcanic rocks. The 

 islands are sometimes referred to as if composed only of recent 

 volcanic and coral formations. The existence of a series of old rocks 

 has been believed from the records of gneiss on Espiritu Santo by 

 Levat, and of ores of iron, copper, and nickel. The asserted presence 

 of these materials suggested that the older rocks of New Caledonia 

 form the foundation of the New Hebrides. The existence of the ores 

 and gneiss is, however, discredited by Sir Douglas Mawson (1905, 

 pp. 422, 434-5) ; he remarked that he had examined " small samples 

 of copper, manganese, and other ores supposed to have been collected 

 in the group" (Mawson, 1905, p. 435). He did not confirm this 

 supposition, though admitting that traces of these metals might 

 occur. 



Lieut. Frederick (1893) obviously identified some of the New 

 Hebrides rocks as " claystones ", which may indicate that he 

 recognized some older sediments. If this statement had beeu 

 confirmed it would have been his most important contribution to the 

 geology of the archipelago ; but it was apparently distrusted, and 

 was excluded from his published paper; and his identification is only 

 known from a remark by Sir Archibald Geikie in the discussion. 



1 [The description of the Volcanic Eruption of 1913 on Ambrym Island, 

 New Hebrides, by the Eev. M. Frater, appeared in the Geological Magazine 

 for November, 1917, pp. 496-503, and was communicated by Professor 

 J. W. Gregory to the Editor.] 



DECADE VI. — VOL. IV. — NO. XII. 34 



