1884.] Microscopic Structure of some Rocks from Ecuador. 133 



and parallel extinction agree with hypersthene. There are scattered 

 crystals of hematite and scales of iron-glance, or possibly small angite 

 crystals iron-stained. The ground-mass appears to be a clear glass 

 thickly studded with dusty ferrite, and with minute crystallites in 

 part, at least, felspar. The rock is, therefore, an augite-andesite, 

 and bears some resemblance to the darker-coloured rock described in 

 Part I from Pichincha. 



Cayambe. 



" The name Cayambe belongs both to a town and to a mountain. 

 The summit of the latter bears north-east by east from Quito, distant 

 45 miles. According to my mercurial barometer observations its 

 height is 19,185 feet, and this is remarkably close to the height 

 obtained by Messrs. Reiss and Stubel by A, which was 19,161 feet. 

 The French Academicians at the beginning of the 18th century made 

 its elevation slightly greater than my determination, and Humboldt 

 does not appear to have measured it. It is fourth in rank of the 

 Ecuadorian Andes, being inferior in altitude to Chimborazo, Coto- 

 paxi, and Antisana. 



" The upper 4,000 feet of Cayambe are almost entirely covered by 

 snow and glaciers, and such small patches of rock as are not covered 

 are indistinguishable at the distance of a few miles. From Quito the 

 mountain has a very noble appearance, but owing to the cloudiness of 

 the atmosphere it is not, perhaps, seen during as much as the fifth 

 of the year. The snow-line on Cayambe is lower than upon Chim- 

 borazo, though the former mountain is almost exactly upon the 

 Equator, and the latter is considerably to the south of it. The upper 

 part of Cayambe is a huge hump, and does not appear cone-shaped 

 from most directions. At the level of 9,000 feet the mountain extends 

 about 18 miles from north to south, and 14 to 15 miles from east to 

 west. 



" Until the time of my journey, it was conjectured that the moun- 

 tain was still an active volcano. We inspected the whole of its slopes 

 fairly well all round, and saw no open crater. It is probable that here, 

 as in other of the Ecuadorian Andes, there was a crater near or at 

 the summit which is now filled with snow. It is certain that Cayambe 

 is not now an active volcano, and that it has been one in the past 

 the numerous streams of lava which are found upon its slopes leaving 

 no possibility of doubt on the subject. 



" Very few rocks being exposed upon the upper part of the moun- 

 tain, I did here as upon Antisana, and collected specimens upon the 

 highest attainable subsidiary peak having rocks uncovered, and from 

 this point (Pointe Jarrin, 16,163 feet), which bears about the same 

 relation to Cayambe as the Aiguille de Gouter does to Mont Blanc, 

 I took specimens of the rocks in situ,, and of the morainic fragments 



