Geographical Collections. 287 
of eternal snow. Many of its peaks surpass the height of 20,000 feet, (3127.5 
toises,) and it contains the most elevated summits gf the Cordilleras which have 
hitherto been attempted to be measured. Those of [limani and of Sorata, 
which are covered with eternal snow, surpass all the gigantic peaks of Columbia, 
of Chimborazo, of Antisana, and Cayamba. 
The Illimani is situated in the Bolivian province of La Paz, twenty leagues 
E. S. E. of the town of that name, (Lat. S. 16° 29’ 30”, Lon. W. 48° 32’.) 
Like the Chimborazo in another chain, it forms the southern extremity of the 
eastern chain of the Andes, to which it belongs. By astronomical observation, 
it is between 16° 35’ and 16° 39’ south lat. and between 67° and 68° west long. 
of Greenwich. Its summit is divided into four peaks, arranged in a direction 
pretty nearly from north to south, or in that of the entire chain. Mr. Pentland 
only succeeded in measuring the most northerly of these peaks: he found its ele- 
vation to be 24,000 feet above the level of the sea, or of 12,000 feet above the 
town of La Paz. But one of its more southerly peaks appeared to Mr. P. more 
elevated by 250 feet, judging from the place on which he stood. The bad wea- 
ther prevented him ascertaining the actual difference of height. 
The determination of the height of the Illimani was accomplished by a trigo- 
nometrical operation, executed on the borders of a little lake at the foot of the 
mountain. The observation of the barometer gave for the elevation of the plain 
where this lake occurred, 15,951 feet above the level of the sea. The length of 
the lake was, in the first place, trigonometrically determined by a good theodo- 
lite, and the angle of the mountain was then taken at the two extremities of the 
lake, with one of Troughton’s sextants and an artificial horizon. The operation 
was easy to execute, and the angles of elevation, measured at the extremities of 
the base, comprehended more than 22°. Mr. P. has supposed in his calculation, 
that the effects of refraction equalled 1-25th of the arc measured. He has never- 
theless reason to think, that in so rare an atmosphere, with a temperature of 6° 
cent. at mid-day, and under a barometric pressure of 431.65 millimetres, this 
element has been considered too high. In this case, the height of the mountain 
would be still greater than has been indicated. The highest point to which Mr. 
Pentland arrived himself, in climbing the Ilimani, was 19,000 feet. He could 
not reach a greater height, not so much on account of the rarefaction of the atmo- 
sphere, as on account of the number of rents which occur in the glaciers which 
must be crossed, for glaciers occur in this part of the Andes. There came on 
besides a viblent storm, which threw clouds of snow into his face, so that he was 
obliged to relinquish the hopes he had conceived, of carrying his barometer to the 
summit of the [limani. 
That point of the coast of the southern sea which lies on the same parallel as 
the Illimani, occurs between Quilca (lat. 16° 41’) and Morro (16° 30’,) and be- 
tween 72° 41’ and 73° 20’ west longitude, by a mean of the observations of Captain 
Hall and of Al. Malaspina. Now the summit of the mountain in question is be- 
tween 67 and 68°. It therefore results that the point -of the coast which is due 
east of the Illimani, is at an horizontal distance of 5° 30’ of an. arc, or, in round 
numbers, 330 nautical miles, which explains why this lofty mountain is conceal- 
ed from navigators by the western chain of the Cordillera, which is between it 
and the sea. 
With respect to geognostic constitution, the Illimani is composed of secondary 
rocks, of transition slates, and of mica slates, altogether similar to those of the 
Alps of Maurienne and Tarentaise in Europe. These beds are traversed by nu- 
merous quartzose veins, containing auriferous pyrites and native gold. Some of 
these veins, though at an elevation of 17,000 feet, have been worked by the an- 
cient Peruvians long before the arrival of Buropesn colonists. 
In the northern region of the eastern chain of the Cordillera, almost in the 
centre of that part of its crest which is covered with snow, and from the centre of 
a group of nevados, rises the mountain of Sorata, under 15° 30’ south latitude. 
This peak belongs, like the Illimani, to the Bolivian province of La Paz, and is 
situated to the east of the village of Sorata, the most remarkable place of the dis- 
