It may be asked how it can be known that the dust was carried this long distance by the wind. May it not as well have been transported by water? The answer must be, in the first place, that showers of the same kind of material have been observed in connection with volcanic outbursts in other parts of the world. One such shower is known to have strewn the same kind of dust on the snow in Norway after a volcanic eruption in Iceland, and after the great explosion on Krakatoa, in 1883, such dust was carried by the wind several hundred miles, and scattered over the ocean. If this ash had been transported by water, it would not be found in such a pure state, but it would be mixed with other sediments. There would, no doubt, also be found coarser fragments of the volcanic products. On the contrary, it appears uniformly fine. No particles have been found which measure more than one millimetre in diameter, and less than one per cent of its weight consists of particles exceeding one eighth of a millimetre in diameter. In seven samples taken from different places the proportions of the different sizes of the grains were about as follows: A = Diameter of grains in millimetres B = Percentage of weight of each size ---+-------+-------+--------+---------+---------+----------+----------- A |1/2-1/4|1/4-1/8|1/8-1/16|1/16-1/32|1/32-1/64|1/64-1/128|1/128-1/256 B | 0.1 | 0.1 | 19 | 37 | 32 | 9 | 1 ---+-------+-------+--------+---------+---------+----------+----------- Flaky particles of this size are easily carried along by a moderate wind. In some places it appears as if the dust were resting on an old land surface where no water could have been standing when it fell. There is really no room for doubt that it was carried several hundred miles by the wind. It must have darkened the sky at the time, and it must have settled slowly and quietly over the wide plains, covering extensive tracts with a white, snowlike mantle several feet in thickness. What a desolate landscape after such a shower! What a calamity for the brute inhabitants of the land!