20 GEOLOGICAL MEMOIRS. 
hand or the outline of the houses. At five inches from the eye even 
a white handkerchief was no longer perceptible. This appearance 
arose from a thick shower of volcanic ashes from an eruption on the 
neighbouring island of St. Vincent. This peculiar rain and the dark- 
ness it produced ceased between twelve and one o’clock in the middle 
of the day, but by the aid of a lantern, the dust had been observed 
to fall several times in the forencon in particular abundance. Some 
trees bent under the weight, others broke, the crash of the branches 
forming a remarkable contrast with the perfect stillness of the air. 
The sugar-canes were completely crushed down, and the whole island 
was covered an inch thick with a layer of greenish ashes. 
The relative position of the islands of Barbadoes and St. Vineent 
gives peculiar interest to this occurrence. The latter island, as is 
well-known, les twenty leagues west of the former. In that region 
the trade-wind, especially m April and May, blows uniformly and 
without interruption from the east, with a slight deviation to the 
north. We must therefore admit that the voleano of St. Vincent 
threw up the immense mass of dust that fell on Barbadoes and the 
surrounding sea, not only to such a height as to be beyond the influ- 
ence of the predominating trade-wind, but also into a region where 
one im an opposite direction prevailed. This is an exceedingly wel- 
come fact to natural philosophers, according to whose theory of the 
trades there must be a constant return-current above from west to 
east, since it is exactly this current which, on the lst of May 1812, 
brought the volcanic dust from St. Vincent to Barbadoes, thus esta- 
blishing the existence of the aérial current which is required to ex- 
plain the phenomena. 
The chemical analysis of a specimen of these ashes brought to 
England, of which Dr. Thomson published a short notice in the 
fourth volume of his Journal in the year 1814, gave m 100 parts: 
1 of iron peroxide, 8 of lime, and 90 of silica and alumia. 
The phenomena on the island of St. Vincent were shortly the fol- 
lowing :— ) 
The Souffrier Mountain, or Morne Garou, the most northern and 
highest summit of the lofty chain which traverses the island from 
north to south, though constantly emitting smoke, had yet never been 
in a state of eruption from 1718 to 1812. About 2000 feet above 
the sea, and scarcely more than two-thirds of its whole height, there 
was a circular ravine about half a mile in diameter and 400 to 500 
feet deep. In the centre of this wide cavity a conical hill, about 200 
feet in diameter, rose to the height of 260 to 300 feet, its lower half 
being thickly covered with brushwood and vines, whilst the upper 
half to the summit was bare and strewed with natural sulphur. From 
fissures in the cone and the intervals of the stones a thin white smoke 
incessantly escaped, sometimes coloured by a bluish flame. At the 
southern and northern base of the cone were two cavities full, the one 
of perfectly pure water, the other of water strongly impregnated with 
sulphur and alum. 
On Monday the 27th of April 1812, exactly at twelve o’clock, 
a tremendous crashing of the mountain, with violent earthquakes, 
