94 TRAVELS A3I0NOST THE ORE AT ANDES, chap. iv. 



Some previous writer has justly said that this place seems 

 like an oasis in a desert. The hills in its immediate vicinity 

 are mostly bare, monotonous ridges covered with volcanic dust, 

 which is set in movement by the slightest breath of air. These 

 surface dusts are a heterogeneous assemblage, to some extent 

 derived from the fundamental soil, and partly by drift from other 

 localities, or by fresh depositions from the most recent eruptions 

 of the yet active volcanoes of the Eepublic. A little way below 

 the surface one comes to a vast deposit of pumice, not in blocks 

 or lumps that would be termed pumice-stone, but in fragments 

 which have been ejected during some terrific convulsion, or period 

 of eruptions. The town of Ambato is built on this deposit.^ The 

 comparative coarseness of the fragments seems to indicate that 

 the place of eruption was not far distant. The largest ones may 

 measure a quarter of an inch in diameter, and weigh as much as 

 J to J of a grain. They more commonly weigh about thirty to a 

 grain, and range in size from "05 to "1 of an inch in diameter. 



Pumice in lumps or masses no doubt exists in large quan- 

 tities in the interior of Ecuador, though I saw little of it. The 

 largest pieces I found in situ were upon the summit ridge of 

 the highest point of Pichincha, and these were scarcely a foot 

 in diameter. Natural blocks of it are sometimes hollowed out 

 and employed as filters, and there was one of these in daily use 

 in the house of Senor Duprat. 



In the course of our journey, this pumiceous dust was met 

 with again, overlain by other dusts which had been ejected during 



1 It has been examined microscopically by Prof. T. G. Bonney and Miss 

 Catherine A. Raisin, who have favoured me with the following report. " The 

 material is mainly a colourless, vesicular pumice. Much of it is quite clear, but 

 many of the fragments have entangled within them some small microliths, and 

 also plates of a pale greenish mica, which occurs occasionally in small clearly- 

 defined crystals, shewing pseudo-hexagonal form ('02 mm. to 'Ol mm. diameter). 

 Some of the mica has a yellowish or brownish colour. Small spheroidal blebs 

 occur within the pumice, brownish and granular, which appear to be a deposit 

 coloured by oxide of iron." 



i 



