1884.] Microscopic Structure of some Rocks from Ecuador. 395 



rocks, and thus lies outside the volcanic zone. I am. again indebted 

 to Mr. Whyraper for the interesting general notes which are pre- 

 faced to the lithological descriptions. 



Altar. 



" This mountain is prohably the fifth in rank of the Ecuadorian 

 Andes, and according to Messrs. Beiss and Stiibel is 17,730 feet high. 

 Owing to long continued bad weather I could neither ascend nor 

 measure it. It is about 40 miles E.S.E. of Chimborazo, and lies S. 

 of Cotopaxi, having nearly the same longitude. 



" In the older maps of Ecuador this mountain is sometimes called 

 Los Collanes, and there is a valley leading from it in a westerly 

 direction still bearing that name. I encamped at the head of this 

 valley close under the main mass of the mountain (12,540 feet) and 

 in the neighbouring valley of Naranjal (13,050 feet) for five days, and 

 experienced during the whole time a succession of storms of wind, 

 rain, hail, and snow, and such observations as could be made were 

 obtained with much difficulty. 



" The peaks of Altar have been considered by previous travellers to 

 fringe the edge of a broken-down crater. Appearances are in favour 

 of this supposition, though there does not seem to be any distinct 

 evidence in support of it. The valley of Collanes leads away from 

 the open, or broken-down side, and if it were followed up to its 

 furthest extremity the traveller would find himself in a vast cirque 

 filled with glacier, and bordered by peaks rising to heights 4,000 feet 

 above his level. The valley of Collanes is not at present occupied by 

 such masses of debris as we should expect to find if there had been 

 any great convulsion which wrecked the western side of the crater. 



" The highest peak of Altar is situated at the head of the valley of 

 - Collanes, on its left bank or southern side. On the opposite side of 

 the crater (i.e., on the right bank or northern side of the valley) there 

 are several points only slightly inferior in elevation to the highest 

 peak ; but at the extreme head of the valley (i.e., the eastern side of 

 the crater) the edge of the rim of the crater is considerably lower than 

 upon its north and south sides. The summit of this depressed part 

 might, in my opinion, be reached from the interior of the crater, but 

 the highest point could not. Its face towards the interior of the 

 crater is as steep as the most abrupt part of the Eigher in the 

 Bernese Oberland, and it is covered with small hanging glaciers. 

 From the exterior of the crater the summit of this peak may perhaps 

 be reached. My assistant, J. A. Carrel, reported favourably upon it, 

 stating that there was a large glacier upon its southem side (which 

 was unseen from the valley of Collanes), and he brought back from 

 the highest point he reached (which was probably about 3,000 feet 

 above our camp) the specimens A and B, taken in situ, and C, a loose 



VOL. XXXVII. 2 D 



