THE ERUPTIONS OF MAY, 1902, AT THE SOUFRIERE IN ST. VINCENT. 
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were collected by Professor Saprer # as felspar basalts, hypersthene-bearing basalts, 
basalts, olivine augite andesites, hypersthene andesite, hypersthene augite andesite, 
and hornblende pyroxene andesite. Professor Lacroix! has classified his specimens 
as andesites, andesilabradorites and labradorites with augite and hypersthene, and 
basalts. Recognising that they all belong to one series and are linked together by 
intermediate types, we shall describe them as hypersthene andesites (with accessory 
olivine and hornblende), hypersthene basalts (with both olivine and hypersthene) and 
olivine basalts; this terminology is more in accordance with the nomenclature current 
in Great Britain. 
The hypersthene andesites, except that they are more or less decomposed, bear a 
strong resemblance to those ejected by the Soufriere during 1902. They are all 
porphyritic, the minerals of the first generation being plagioclase, augite, and 
hypersthene, while the groundmass consists of augite, plagioclase, and iron oxides. 
Magnetite and apatite are constantly present; hornblende occurs in a few specimens, 
as in the recent bombs of the Soufriere. Olivine is more common, and is often 
surrounded by a resorption border of hypersthene. Small nodules or glomero- 
porphyritic groups of hypersthene are common in these rocks, and represent the final 
stages of resorption of olivine (Plate 26, fig. 2). They often contain branching growths 
of magnetite at their centres, showing that part of the iron oxides was rejected in the 
transmutation from olivine to hypersthene. The hypersthene is usually idiomorphic, 
but when the matrix is comparatively well crystallised, a zone of augite surrounds it, 
and has probably formed by corrosion of the hypersthene during the last stages of 
crystallisation of the groundmass. The porphyritic felspars are much zoned, con¬ 
sisting of bytownite (80 per cent, anorthite) at their centres, while their margins are 
acid labradorite and andesine. The groundmass felspars are andesine (about 
40 per cent. An), and occur as small elongated laths ; the augite of the second 
generation is granular and usually anhedral. Most of these rocks contain little 
glassy base, and are far less rich in this substance than the recent bombs of the 
Soufriere, but had the latter cooled slowly as in a lava flow, they would have very 
much the same structure as many of the older andesites. 
As indicated by the ejected blocks of the 1902 eruption, there is much hypersthene 
andesite in the Soufriere, though hypersthene basalts occur there also, and Professor 
BergeatJ mentions two olivine basalts from the Black Ridge on the mountain. 
Hypersthene andesites are exposed at Morne Ronde, Larikai, and Baleine, and occur 
also at Cumberland, north of Chateaubelair. 
The hypersthene basalts are richer in olivine than the hypersthene andesites, but 
contain less hypersthene (Plate 27, fig. 5). They may be defined as consisting of 
plagioclase, augite, olivine and hypersthene, with the last two minerals in nearly 
* Karl Sapper, ‘In den Vulkangebieten Mittelamerikas and Westindiens,’ p. 194 (1905). 
t Op. cit., p. 592. 
| In Karl Sapper, ‘In den Vulkangebieten Mittelamerikas und Westindiens,’ p. 194 (1905). 
2 T 2 
