326 
PR. JOHN S. FLETT: 
PETROGRAPHICAL NOTES ON THE PRODUCTS OF 
hypersthene basalts were emitted. The latest eruptions have been entirely of the 
spasmodic type, the effusive having given place to the explosive phase. This may 
not be without significance, especially seeing that most of the great explosive outbursts 
of recent years, Krakatoa, Bandaisan, Tarawera, Santa Maria, &c., have been produced 
by andesitic magmas. This may be explained by supposing that a magma of this 
nature retains its steam in solution till it is on the point of solidification, and then 
releases it suddenly with great violence. 
The Dusts that fell in Barbados in 1812, October 1902, and March, 1903. 
By the kindness of Sir Daniel Morris and of the Bev. N. B. Watson, vicar of 
St. Martin’s, Barbados, we have received specimens of all the dust-falls of volcanic ash 
from St. Vincent, which are known to have taken place at Barbados. Their dates 
are May 1 , 1812, May 7, 1902, October 16, 1902, and March 22, 1903. All consist 
of the same minerals and have very much the same appearance. They differ slightly 
in colour and in coarseness. The dust of 1812 is distinctly paler brown than that of 
May 7, 1902, and that of March 22, 1903, is rather darker. The dust of October 16, 
1902, is very fine and of a grey colour, resembling in this respect the finer dusts 
from Montague Pelee in Martinique. It is the lightest coloured of all the Soufriere 
dusts which have fallen in Barbados. 
Samples of these dusts were passed through sieves having 30, 60, and 90 meshes 
to the inch. This gives a rough test of the size of the component grains. The 
meshes of these sieves were measured under the microscope and proved to have the 
average diameters stated in the last column of the table. 
Meshes to 1 inch. 
1812. 
May 7, 1902. 
October 16, 1902. 
March 22, 1903. 
per cent. 
per cent. 
per cent. 
per cent. 
mm. 
30 retains . . . 
0-17 
0 
— 
o-o 
>0-73 
60 „ ... 
11-76 
5 
— 
o-l 
>0-31 
90 „ ... 
7-97 
26 
1-8 
0-2 
>0-19 
90 passes . . . 
80-10 
69 
98-2 
99-7 
— 
These show that the 1812 dust contained most coarse particles. Many of these 
were small vesicular pieces of pumice, very light, and hence likely to be transported 
to a great distance. The dust of May, 1902, is coarser than any other Barbados dust 
of the recent eruptions, probably because it had been projected into the air with 
greater violence and to a greater height; hence, when the cloud passed eastwards over 
Barbados, it still retained a larger proportion of the coarser particles. 
The minerals of these dusts are the same as those of the May eruptions of 1902. 
All contain plagioclase felspars, augite, hypersthene, and olivine. Hornblende was 
seen only in the dust of May, 1902. Glassy material, more or less devitrified by 
