THE 



PROCEEDINGS 



OF 



ROYAL SOCIETY. 



January 6, 1887. 



Professor STOKES, D.C.L., President, in the Chair. 



The Presents received were laid on the table, and thanks ordered 

 for them. 



The following Papers were read : — 



I. " On the Occurrence of Silver in Volcanic Ash from the 

 Eruption of Cotopaxi of July 22nd and 23rd, 1885." By 

 J. W. Mallet, M.D., F.R.S., University of Virginia. 

 Received November 26, 1886. 



A few months ago I received from Senor Julian R. Santos, of 

 ^Ecuador, formerly a pupil of mine in the laboratory of this Univer- 

 sity, a specimen of volcanic ash collected at his place of residence, 

 Bahia de Caraguez, on the coast of the Pacific, about 120 miles nearly 

 •due west from Cotopaxi. This, the highest and among the most 

 mighty of the active volcanoes of our globe, burst forth into eruption 

 about 11J p.m. on the 22nd of July, 1885, and the ash began to fall 

 .at Bahia de Caraguez at 7 a.m. on the next day, the 23rd. It fell 

 there to the depth of several inches, this fact alone indicating the 

 discharge of an enormous amount of solid matter into the atmosphere, 

 although Senor Santos wrote to me that the unsettled condition of 

 the country, disturbed by revolutionary movements, prevented his 

 making extended enquiries which might have ascertained the area 

 covered by the fall of ashes. 



The specimen sent me consisted of a very finely divided powder, 

 mobile and soft to the touch, of light brownish-grey colour. Under 

 the microscope it appeared to be made up of minute granules and 

 spicules, in general with sharp, more or less splintery edges. These 

 were for the most part colourless and transparent, or white and trans- 

 lucent; some were reddish, some dark bottle-green, some brown, 

 some black and opaque. Most of those clear enough to freely trans- 

 mit light showed brilliant colours in a field of polarised light. Quartz, 

 two felspars (one white, and one pink or reddish), augite, magnetite 



VOL. xlii. B 



