﻿632 DR. TEMPEST ANDERSON ON THE [Nov. I9IO 



especially to the west or leeward of the point, are beds of black 

 sand capping the lava. This appears to be wind-borne and the 

 product of the explosions. The streams vary much from day to day, 

 and even from hour to hour. When I saw them for the first time 

 at night from the steamship Atua, there were twelve visible by 

 their own light; a second time, seen from a native schooner, they 

 were fewer and quite different. On a third occasion, when I got 

 as near as possible in a boat, the lava was flowing in four large 

 and distinct streams, and more would probably have been visible 

 at night (PI. L, fig. 1). I was anxious to observe the formation 

 of pillow-lava and we got as near as possible without melting the 

 pitch-caulking of the boat. Where the discharges were most active 

 explosions were almost continuous, and the whole was obscured by 

 clouds of steam from which fragments of red-hot lava and showers 

 of black sand were seen to fall (PI. LI). Where the lava was 

 flowing in smaller quantity explosions were much less noticeable, 

 and the lava extended itself into buds or lobes. The process was 

 as follows : an ovoid mass of lava, still in communication with its 

 source of supply and having its surface, though still red-hot, 

 reduced to a pasty condition by cooling, would be seen to swell, or 

 crack, into a sort of bud with a narrow neck like a prickly pear on 

 a cactus, and this would rapidly increase in heat, mobility, and 

 size, till it either became a lobe as large as a sack or pillow, like 

 the others, or perhaps stopped short at the size of an Indian club 

 or large Florence flask. Sometimes the neck supplying a new lobe 

 would be several feet long and as thick f} r <t man's arm, before it 

 expanded into a full-sized lobe ; more commonly it would be 

 shorter, so that the freshly-formed lobes were heaped together. 

 They looked white-hot even in daylight, and, as the waves washed 

 over them, the water seemed to fall off unaltered without boiling, 

 owing probably to its being in the spheroidal condition. 1 I have 



1 The structure thus produced is analogous to that to which the term 

 pillow-structure, originally applied to a peculiar and exceptional form 

 of spheroidal jointing, has of late years been often extended. 



It is very satisfactory to me to find that the mode of formation that I have 

 observed is in accord with the views previously expressed as probable on other 

 considerations by such careful observers as (in chronological order) : — 



Cole, G-. A. J., & Gregory, J. W. ' Variolitic Rocks of Mont Genevre 

 Quart. Journ. Geol. Soc. vol. xlvi (1890) p. 311 (and in litt.). 



Teall, J. J. H. Trans. Roy. Geol. Soc. Cornwall, vol. xi (1893-95) 

 pp. 562-64 & pi. facing p. 565. Also along with Dr. B. N. Peach & 

 D. J. Horne. 'The Silurian Rocks of Scotland ' Mem. Geol. Surv. 

 1899, pp. 84, 431, etc. & pis. iv, vi. 



Geikie, Sir Archibald. ' Ancient Volcanoes of Great Britain ' vol. i 

 (1897) pp. 25 & 193. 



Foreign authorities on pillow-lava are :— 



Dana, J. D. Amer. Journ. Sci. ser. 3, vol. xxxiv (1887) p. 362; and 

 ' Characteristics of Volcanoes ' New York, 1890, pp. 9, 241, & 243. 



Platania, G., in Dr. Johnston-Lavis's 'South Italian Volcanoes' 1891, 

 pp. 41-42 & pi. xii. 



Daly, R. A. ' Variolitic Pillow-Lava from Newfoundland ' Amer. 

 Geologist, vol. xxxii (1903) pp. 74-78, with a discussion and references. 



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