APPENDIX— NOTE ON ROCKS FROM THE ANDES. 143 



t.'otoiiaxi ; one of them having been ejecteel l)y that volcano and collected 

 upiiu the slopes of Chimin nazo under the exceptionally interesting circum- 

 stances detailed in his narrative. Of these it may suffice to say that they 

 consist of minute lapilli, chips of vijlcanic glass, and fiugnients of crystals of 

 plagioclastic felspar, augite, and hypersthene (I have noticed one or two vei'v 

 characteristic crystals of the last). They are in shoi't the mateidals which 

 one might expect to ol)tain from the explosive destruction of lavas such as 

 occur on the cone of the mountain. The glass is moderately solid, difiering 

 thus (for example) from the very vesicular ejectments of Krakatoa — the 

 constant ' puffing ' of Cotopaxi probably preventing the accumulations of 

 such a large amount of steam as to permeate completely the more or less 

 molten matter in the pipe of the crater. The dust which fell on Chimborazo, 

 after an aerial voyage of full 65 miles, consisted of fragments varying from 

 about four -thousandths of an inch downwards, A'ery many ranging fi'oni 

 al)0ut one-thousandth to three-thnusandths. Specimens of a coarser iisli of a 

 pumiceous character have also been brought, which no doubt also belongs to 

 the same group as the more solid rocks. 



