124 Prof. T. G. Boniiey. On the [June 19, 



No. IV (the dust from Riobamba) does not appear to me to differ 

 materially from No. II, except that perhaps it is very slightly coarser, 

 and the glass chips appear to be a little more vesicular, and so there is 

 a somewhat larger proportion of fragments of colourless or almost 

 colourless pumice. 



No. V (Quito). A slightly paler dust than No. II, with which its 

 constituents correspond more nearly than with the first, but there are 

 a few more of the opaque scoriaceous fragments described in the latter, 

 and the grains occasionally attain a diameter of '007 or '008 inch. In 

 the brown glass chips, however, vacnoles, commonly spherical, some- 

 times elongated, are abundant ; many of them range from about '0001 

 to "0002 inch in diameter, but some are still smaller. 



In No. VI (Chillo) there are occasionally fragments about '01 inch 

 in diameter, but they appear to be less common than in the other 

 slides, and chips not exceeding '002 inch diameter predominate. 

 These are glass and mineral fragments, as above ; lapilli appear to be 

 very rare. I think the glass is rather more vesicular than is the case 

 in No. II, but in all these samples of dusts which have travelled for 

 BO considerable a distance from the volcano I do not consider the 

 differences more than varietal, and we have in them the debris of 

 a microporphyritic hyperstheniferous augite-andesite. 



No. VII. A dust consisting of dark granules, mixed with light 

 grey and reddish specks. The materials are rather coarse, the 

 granules commonly ranging from about '01 to '015 inch. The most 

 abundant are minute lapilli of scoriaceons aspect and dark colour, 

 almost black ; in less numbers are glassy whitish and reddish 

 granules : with these occur fragments of felspar, angite, and hyper- 

 sthene. Of the latter mineral there was a fairly perfect crystal about 

 015 long, which exhibited a very marked and characteristic dichroism 

 and extinction. The granular character and comparative coarseness 

 of the dust readily distinguishes it from the other examples, and 

 brings it nearer to those described from the locality of the first 

 tenh 



I am indebted to the kindness of Professor Judd, not only for 

 having a series of the above volcanic dusts excellently mounted for me 

 in his laboratory, but also for the gift of two slides of the materials 

 ejected from Krakatoa in the eruptions of last year. Of these, one is 

 a specimen of the pumice found floating in the Sunda Straits, a 

 vesicular clear glass, like some viscid fluid " whipped " to a foam and 

 then allowed to flow, which presents but little resemblance to the 

 materials ejected from Cotopaxi. Neither does the other specimen 

 (from the ash which fell at Batavia, after a journey of 95 miles) 

 present a marked resemblance, for although there is a general simi- 

 larity in the presence of mineral fragments of the same species, yet 

 the rock fragments differ in the predominance of glasses allied to that 



