Vol) 56: | THE ERUPTION AT ST. VINCENT. 369 
pieces of glass are grey or brownish in colour, turbid or spotted, 
full of very small steam-cavities, and between crossed nicols show 
sometimes small, elongated, doubly-refracting microliths. In most 
cases the larger pieces are of composite character, and consist of a 
fragment of felspar with more or less of adherent glass. 
Among the finest débris there is much felspar in very minute 
angular chips, but pyroxene in this condition is less common. 
The great preponderance of crystalline materials in this volcanic 
dust is one of its distinctive features, and shows that in the lava 
before the great eruption an early generation of crystals was 
developed in considerable perfection and abundance. 
Another feature worth notice is the perfect crystalline form, not 
seldom exhibited by the felspar and the pyroxenes, and the very 
inconsiderable amount of glass that often surrounds them. At the 
time when the mass was projected into the air the glass must have 
been very fluid, and must have been to a large extent wiped off the 
surface of the crystals by friction with the atmosphere during its 
rapid passage. 
Dr. Morris reports that ‘ the ash at first was of a brownish colour, 
then it became slightly redder,’ while the final deposits consisted of 
a whitish-grey impalpable powder. This may be explained by 
supposing that the minerals of high specific gravity were first to 
fall. The magnetite and the pyroxenes would first subside, and 
appear biack or dark-brown from adherent films of brown glass ; 
thereafter the felspars, paler, but brownish for the same reason ; 
and the last to fall would be the minute threads of glass and the 
smallest débris of felspar, which would form a whitish-grey 
impalpable powder. 
A complete chemical analysis of this ash is appended, and as 
the state of the material offers considerable facilities for mineral 
separations, it is hoped that at a future time it may be possible to 
obtain separations and analyses of the constituents, more especially 
the felspars. The chemical analysis is as follows :— 
Per cent. 
OO ee cae tas Mare So plet detects delta 52°81 
BIG. SUA ie ithe San a aR ea 0°95 
EBON Piece ee ee iol snes oc ve eak 18°79 
BO Ae jase dsc 2 dl itea ene tac 3°28 
SCO yey se Ee Fe hock eve weke oe ne 4°58 
WT ee eee ts ears nc ev edenens sae 0:28 
(COSTE OE AEE Als ee ae 0:07 
CAO Re erento tence Mie nae fac 9°58 
BA ee ey ae 5°19 
UU Bere Ec oe ee 0:60 
1 B08 J eRe oy ee ne ee 3°23 
EO bree eee napeins ie sen teas neue 0-15 
SCL ANN Ce aie atk eS a 0°33 
(2) PR El Sen ae A rE 0-14 
EO ate VOR CCM: ocd olae eet base 0:20 
EB Orabove 105% Cent ss. .2p se a0. O17 
