
> it 
~ Pant lL. Sucr.i§2] VOLCANIC DUST. 217 
~ mountain, but travelled as far as Ascoli, which is 56 Italian miles 
distant from the volcano on one side, and as Casano, 105 miles on the 
other. The eruption of Cotopaxi, on June 26th, 1877, began by 
an explosion that sent up a column of fine ashes to a prodigious 
height into the air, where it rapidly spread out and formed so dense 
- a canopy as to throw the region below it into total darkness. So 
quickly did it diffuse itself, that in an hour and a half a previously 
bright morning became at Quito, 83 miles distant, a dim twilight, 
which in the afternoon passed into such darkness that the hand placed 
before the eye could not be seen. At Guayaquil, on the coast, 150 
miles distant, the shower of ashes continued till the Ist of July. Dr. 
Wolf collected the ashes daily, and estimated that at that place there 
fell 315 kilogrammes on every square kilometre during the first 
thirty hours, and on the 30th of June, 209 kilogrammes in 12 hours.’ 
Probably the most stupendous outpouring of volcanic ashes on record 
was that which took place, after a quiescence of 26 years, from the 
volcano Coseguina, in Nicaragua, during the early part of the year 
1835. On that occasion utter darkness prevailed over a circle of 35 
miles radius, the ashes falling so thickly that, even 8 leagues from 
the mountain, they covered the ground to a depth of about 10 feet. 
It was estimated that the rain of dust and sand fell over an area at 
least 270 geographical miles in diameter. Some of the finer 
materials, thrown so high as to come within the influence of an upper 
air-current, were borne away eastward, and fell, four days afterwards, at 
Kingston, in Jamaica—a distance of 700 miles. During the great 
eruption of Sumbawa, in 1815, the dust and stones fell over an area 
of nearly one million of square miles, and were estimated by Zollinger 
to amount to fully fifty cubic miles of material, and by Junghuhn to 
be equal to one hundred and eighty-five mountains like Vesuvius. 
An inquiry into the origin of these showers of fragmentary 
materials brings vividly before us some of the essential features of 
volcanic action. We find that bombs, slags, and lapilli may be thrown 
up in comparatively tranquil states of a volcano, but that the showers 
of fine dust are discharged with violence, and only appear when the 
voleano becomes more energetic. Thus, at the constantly, but 
quietly, active volcano of Stromboli, the column of lava in the pipe 
may be watched rising and falling with a slow rhythmical movement. 
At every rise the surface of the lava swells up into blisters several 
feet in diameter, which by-and-by burst with a sharp explosion that 
makes the walls of the crater vibrate. A cloud of steam rushes out, 
carrying with it hundreds of fragments of the glowing lava, sometimes 
to a height of 1200 feet. It is by the ascent of steam through its 
mass that a column of lava is kept boiling at the bottom of the crater, 
and -by the explosion of successive larger bubbles of steam that the 
various bombs, slags, and fragments of lava are torn off and tossed 
into the air. It has often been noticed at Vesuvius that each great 
concussion is accompanied by a huge ball-like cloud of steam which 
1 Neues Jahrb. 1878, p. 141. - 
