140 TRAVELS AMONGST THE GREAT ANDES, chap. vii. 



I did clean that meat with our blacking-brush, and wipe out the 

 pots with a pocket-handkerchief. 



Our camp was pitched upon and was surrounded by matter 

 ejected from the volcano, to which the terms dust, sand, lapilli, 

 and ash are usually given. The finest particles are termed dusts, 

 coarser ones are called sand and lapilli. The term ash covers 

 all three expressions, and in this sense I have used it elsewhere. 

 It is, however, open to the double objection that it conveys no 

 exact idea of either the dimensions or quality of the particles, 

 and suggests a quite erroneous idea. In using the term ash (or 

 ashes) we generally mean the residue of something which has 

 perished by fire. Thus we speak of the ash of paper, tobacco, 

 or coal ; and, when this expression was first applied to matter 

 ejected by volcanoes, those who employed it were no doubt under 

 the impression that the particles which they so designated were 

 actually the residue of something which had been consumed by 

 fire. This idea would be fostered by the matter very commonly 

 being of an ashy colour.^ Close investigation of the materials shews 

 that there is scarcely anything (or nothing) of the nature of ash 

 amongst them. They are composed of rocky and mineral frag- 

 ments. The rocky ones are often angular chips of lava, while 

 felspar constitutes a large proportion of the glassy ones. Frag- 

 ments of scoria (scum of lava) are common, and magnetic particles 

 are always present in the Cotopaxi dusts. 



It is a rather troublesome peculiarity of volcanic dust that 

 it will penetrate anywhere. The extreme fineness of the more 



' A number of the volcanic dusts I collected in Ecuador have this appearance 

 when seen in hulk. Some incline towards slaty-grey, while others are of slightly 

 warmer hues. Under very moderate magnifying power it is, however, seen that the 

 particles are rather sharply divided into very light-coloured glassy fragments, and 

 very dark rocky ones. The ashy colour is produced by the admixture of the two 

 classes of atoms. Several of these Cotopaxi dusts have been examined microscop- 

 ically by Prof. T. G. Bonney, F.R.S., and are described by him in the Pro- 

 ceedings of the Royal Society^ June, 188-4. Those who are desirous of pursuing this 

 subject are referred to that paper. 



