CHAP. IV. 



PUMICE. 



95 



subsequent eruptions. At the town of Machachi, more than 

 fifty miles away, it was found ten feet below the surface, covered 

 by three beds of volcanic ash which amounted in the aggregate 

 to 52 inches in thickness, 

 of an entirely different 

 nature, each having a 

 strongly marked character 

 of its own. The pumice 

 here is in extremely min- 

 ute fragments. It is rare 

 to find amongst it one as 

 much as -^ of an inch in 

 diameter. The majority 

 are much smaller, and 

 many thousands go to a 

 grain. From the critical 

 examination to which it 

 has been subjected, there is 

 no doubt that the pumice 

 at Machachi was ejected 

 at the same period as that 

 at Ambato ; and from hav- 

 ing superimposed upon it 

 other vast beds of ash, from 

 eruptions which occurred 

 beyond the range of his- 

 tory, one may conclude 

 that it is amongst the 



older of the more recent volcanic products of Ecuador. It is the 

 invariable rule with volcanic dusts that the grosser particles settle 

 first ; and, as the finest ones are found much to the north of Am- 

 bato, it would appear that the dominant winds, at the time the 

 dust was blown into the air, were directed from south to north. 

 There were some pleasant walks on the western side of the 



A PUMICE FILTER AT AMBATO. 



