632 
DR, TEMPEST ANDERSON ON THE 
[XoY. 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 Atuci , 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 as a 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 jointiug. 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, Gf. A. J., & Gregory, J. W. ‘ Variolitic Eocks of Mont Genevre/ 
Quart. Journ. Geol. Soc. vol. xlvi (1890) p. 311 (and in litt.). 
Teall, J. J. H. Trans. Eoy. Geol. Soc. Cornwall, vol. xi (1893-95) 
pp. 562-04 & pi. facing p. 565. Also along with Dr. B. N. Peacii & 
J). J. Horne. ‘The Silurian Eocks 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. E. A. ‘ Variolitic Pillow-Lava from Newfoundland ’ Amer. 
Geologist, vol. xxxii (1903) pp. 74-78, with a discussion and references. 
