1884.] Microscopic Structure, of some Rocks from Ecuador. 127 



" The whole of the upper part of Chimborazo is crowned by snow- 

 covered glacier, forming a glacier plateau, from which numerous 

 glaciers take their rise. In passing around the mountain I remarked 

 twelve glaciers, all of considerable size, flowing from this plateau. 

 The glaciers have their greatest development upon the eastern and 

 north-eastern sides of the mountain. There is one to the south- 

 south-west of the second summit, that is wholly formed by the 

 re-consolidation of glacier ice, which falls over the great cliffs at its 

 head. This glacier we called Glacier de Debris. The clean sections 

 which are exposed in the upper glacier by its breaking away and 

 falling over the above-mentioned cliffs show that the ice sheet on the 

 summit is more than 200 feet in thickness. 



" I found roches montonnees upon Chimborazo, in a valley (or vallon) 

 leading in a south-westerly direction from the second summit. In 

 this valley there is not at the present time any glacier, and this is 

 the only place in the whole of the Andes of the Equator where 1 

 have observed roches montonnees at any considerable distance from 

 existing glaciers. Retrograding and advancing glaciers may, how- 

 ever, be remarked in various places. On the north-eastern side of 

 Chimborazo some very large moraines which are in the vicinity of 

 the existing glaciers, indicate they were of much greater magnitude 

 in some previous period. It may be that many more traces of glacier 

 action would be apparent if the rocks of this region disintegrated less 

 easily. 



" The average level to which the glaciers descend on Chimborazo 

 may, I think, be stated at 15,600 feet. The snow line is approxi- 

 mately 1,000 feet higher. 



" The whole of the apex of Chimborazo is enveloped by snow- 

 covered glacier, and upon the immediate summit there is a con- 

 siderable (and slightly concave) plateau, on the rim of which the two 

 crowning snow-domes are situated. The more northern of these two 

 is slightly the loftier, and there can be little doubt that they cover the 

 highest points of the rim of the crater of the old volcano, and that the 

 hollow plateau lying between them is the filled-up crater itself. 



"The highest rock which we noticed upon either of our ascents 

 was about 1,000 feet below the summit, a scoriaceous lava, which 

 appeared in small patches, and was apparently in consolidated beds. 

 The highest rock in situ beneath this which we were able to collect 

 was. at the height of 18,400 feet, from the lower beds of the great 

 cliffs facing the south, which support the second summit. It is a 

 trachyte of a coarse red colour, and is one of the most common rocks 

 on Chimborazo. Above it, disposed in parallel bands, were a large 

 variety of strata of various natures, and of widely different colouring ; 

 and upon the rare occasions that these cliffs were lighted by the sun 

 they presented an appearance as attractive as the well-known slopes 



