1884.] Microscopic Structn e of some Rocks from Ecuador. 119 



" Although the final cone of Cotopaxi is externally principally coated 

 with a deep bed of ash, and is, upon the whole, very regular in form 

 and slope, and is almost featureless, it may be remarked : (a.) That 

 on its northern side, extending close up to the rim of the crater, there 

 is a large piece of almost perpendicular precipice, upon which neither 

 ash nor snow can repose. This resembles the great cliffs which I 

 have referred to as occurring near the summit of Chimborazo on its 

 southern and north-western sides, (fe.) That although the ash upon 

 the final cone of Cotopaxi is exceedingly warm (at a depth of 8 feet 

 in it we found it had a temperature of 110 F.), there are intermixed 

 with it streaks of snow and ice, which, being blackened, are not 

 readily perceived, and are somewhat dangerous to the traveller. 



" From a little below the foot of the final cone (say 1,500 feet below 

 the summit) I observed glaciers on each side of the ridge we ascended, 

 which glaciers extended downwards for 1,800 feet, and perhaps con- 

 siderably lower. I could neither trace their beginnings nor their 

 ends, owing to the large amount of ash and debris with which they 

 were coated. 



" At no part of the country which we traversed on the south-west 

 and west of Cotopaxi was the soil much fissured by earthquake cracks ; 

 but the region on the south, and bearing round to the south-east, was 

 cracked and fissured in the most extraordinary manner. We had 

 a good distant view of this from our first camp, and I much regretted 

 that the constant demands on my time rendered it impossible for me to 

 examine it more closely. 



" The country which we traversed on the west of Cotopaxi, at a 

 distance of 5 to 10 miles from the crater, was covered with very 

 numerous rudely spherical masses of scoria, which had been ejected 

 apparently by the volcano ; and the same were noticed near the 

 Quito road, south-south-east of the crater, at even greater distances. 

 These masses measured 3 or 4 feet diameter downwards. I could not 

 find any person who had ever known a considerable fragment to be 

 ejected, and the natives in general seemed inclined to ridicule the idea 

 that they had been thrown out." (E. W.) 



The specimen taken from the summit ring of the crater of Cotopaxi 

 is a compact rather heavy rock (specific gravity =2'656), of a dull 

 warm-grey colour, faintly speckled or mottled with white spots. It 

 has a roughish subconchoidal fracture, and on the joint faces is a 

 dull indian-red colour. The specimen is in good condition. 



The rock under the microscope is seen to contain a considerable 

 number of crystals of a triclinic felspar scattered about in the ground- 

 mass. These commonly vary from about '02 to '05 in the longer 

 diameters, but are occasionally both larger and smaller. They 

 exhibit more or less oscillatory twinning, and an. occasional zonal 

 structure. The majority appear to be labradorite. The outer angles 



