317 
THE ERUPTIONS OF MAY, 
1902, AT THE SOUFRIERE IN ST. VINCENT. 
have at the same time very little in common with the rocks which have been 
weathered under atmospheric conditions, or with the propylites. It seems probable 
that steam, acting at high temperatures and pressures, was the modifying agency. 
Perhaps these rocks lined fissures beneath the crater through which gases ascended 
after the eruptions of 1812 and 1718. 
In St. Vincent quartz-bearing andesites are rare ; in Martinique, where the magma 
was more acid and the volcanic activity more continuous, they are common. Professor 
Lacroix has some very interesting notes on these rocks. They did not appear at 
the first eruptions; but in 1904 the materials produced by the rupture of the dome 
were full of quartz. He concludes that it arose in those rocks which were situated 
beneath the surface of the dome, and were affected for a long period by steam 
emitted from the magma.* 
Cordierite Andesites. 
Six months after we left St. Vincent Professor Lacroix found two specimens of 
cordierite-bearing rocks on the Soufriere, one an andesite, the other a variety of 
quartzite. In our collection there are no cordierite-bearing rocks ; probably they 
were not emitted by the first eruptions; if they were, they must have been very 
scarce. At Martinique, quartz andesites and cordierite andesites were not obtained 
till the volcano had been in activity for some months. Some of these rocks seem to 
bear a close relationship to the quartz andesites above described, but for particulars 
regarding them we may refer to Professor Lacroix’s monograph on Montague Pelee 
(p. 597). 
Anorthite- Olivine Blochs. 
Many crystalline masses, consisting mainly of anorthite and olivine, with augite, 
hypersthene, and hornblende, occurred among the new ash deposits. They were 
mostly in a perfectly fresh condition; some, however, must belong to previous 
eruptions, as their minerals show decomposition. In St. Vincent, several people 
showed us similar blocks which had been picked up on the Soufriere before 1902 ; we 
also saw these blocks in the older tuffs and lavas of the mountain. They occur also 
in Martinique, St. Kitts, and other islands of the Antilles. 
They present a great diversity of appearance in the hand specimens. All are rich 
in felspar, which is usually milky white rather than glassy and transparent. Olivine 
in rounded, greenish yellow, or brownish grains, is the next mineral in abundance, 
and then augite in black crystals which are pale green in thin sections. Dark 
elongated prisms of hornblende are common in some of these rocks. Of the ferro- 
magnesian minerals hypersthene is the least frequent. 
They have usually the appearance of granular crystalline rocks, the grains ranging 
in size from half-an-incli downwards. Some contain larger crystals, which give them 
* Op. cit., p. 521. 
