CHAP. VII. VOLCANIC DUSTS. 141 



minute particles permits it to get into places which might be 

 deemed inaccessible. It floats in the air, travels round corners, 

 and insinuates itself through cracks into sheltered places which 

 cannot be reached by objects falling directly from the heavens, 

 and when settled in them it is secure against disturbance by 

 wind. Whatever falls upon open ground, on the contrary, is 

 wafted hither and thither by the slightest breeze,^ and thus the 

 traces even of considerable eruptions are speedily confused with 

 previous ones.^ There was a good illustration of this in the im- 

 mediate vicinity of our camp. In all the cavernous recesses of 

 the scoria, and in other sheltered places, there was a thick 

 deposit of a dust of a very marked granular character, in appear- 

 ance, though not in constitution, quite unlike any other I 

 obtained.^ This had evidently, from the thickness of the deposit, 

 been ejected during a somewhat severe eruption, and must have 

 fallen everywhere. Though found in every hollow or protected 

 place, it could not be identified anywhere else. Yet this was a 

 rather coarse dust, the predominant particles weighing about two 

 thousand to a grain, and the largest ones measuring '04 of an inch 



1 Upon this account, travelling in tiie interior of Ecuador during dry weather 

 is often exceedingly unpleasant. It is sometimes impossible to face the clouds of 

 dust which are raised. With myriads of sharp, glassy and rocky fragments con- 

 stantly drifting about, it is not surprising that eye complaints are common amongst 

 the natives. 



^ This was the case with the dusts which were ejected during the great eruptions 

 of 1877. By general consent, they fell most heavily around Machachi ; and, accord- 

 ing to Antonio Kacines, covered everything to a depth of more than two inches, 

 and obliged the inhabitants to drive their animals elsewhere for food. At the 

 time of our stay, he could not point them out anywhere as a distinct stratum, as 

 they had been dispersed by wind, or turned over in the course of agriculture. 



3 "A dust consisting of dark granules, mixed with light grey and reddish 

 specks. The materials are rather coarse, the granules ranging from about "01 to 

 •015 inch. The most abundant are minute lapilli of scoriaceous aspect, and dark 

 colour, almost black ; in less numbers are glassy whitish and reddish granules ; with 

 these occur fragments of felspar, augite, and hypersthene. Of the latter mineral 

 there was a fairly perfect crystal about -015 long. . . . The granular character 

 of the dust readily distinguishes it from other examples. "—Prof , T, G. Bonney. 



