286 Geographical Collections. 
which one was meant to rectify some mistakes which had crept into the too hasty 
publication of his principal observations in the French journals. 
“¢ Shortly after my arrival at Lima in 1826, (says Mr. Pentland,) I received from 
my Government an order to explore.the provinces of High Peru, I in consequence 
went by Arequipa to Puno, traversing the western chain of the Andes. I 
coursed through the provinces of Lampa and of Puno, and the banks of the cele- 
brated lake of Titicaca, whose surface includes more than 6000 square miles. I 
visited the islands of Titicaca and of Coata, which are covered with the ruins of 
edifices of the ancient civilization of Peru. I saw the more recent, but still 
more surprising remains of Tia Huanaxo. I passed a few weeks in the rich town 
of Lia Paz, and from thence I went by Oruro and the valley of Desaguadero, to 
Potosi, Tupisa, and Tarija. I afterwards came back to the north, to Chuqui- 
saca. After remaining two months in this latter town, and after having explored 
the provinces of Chayantes, Yauriparaes, &c. I went to Cochabamba, and from 
there, by crossing the eastern Cordillera in the neighbourhood of Paria, I came 
back to the province of Pacajes and to La Paz. It was my wish to have explor- 
ed the districts of Apolabamba and of Larecaja; but having received from the 
British Government orders to depart for Europe, I a second time crossed the 
western branch of the Andes, between La Paz and Tacua. I quitted Peru in 
the month of May 1827, and touched on my return at Rio Janeiro.” 
Mr. Pentland made at Lima and at Callao a considerable series of observa- 
tions, to determine the diurnal and horary variations of the barometer at these 
two stations. These observations have been sent to Mr. de Humboldt. The 
mean height of the barometer at Callao, reduced to the level of the sea and to 
the temperature of 0, and corrected for the effects of cappilarity, is of 761 milli- 
metres. That which was observed at Lima is of 749.52 millimetres, at a tem- 
perature of 15.6° cent. which gives for that town an elevation of 79.75 toises 
above the southern ocean. The instruments employed were two excellent baro- 
meters of Fortin. Mr. Pentland had the good luck, during all his excursions 
into the mountains, to preserve them in the best condition. He has in conse- 
quence made, by means of the barometer, the measurement of several hundred 
points of elevation, on which the greatest confidence can be placed. Lastly, he has 
taken trigonometrical measurements of the height of several peaks whose eleva- 
tion surpasses that of Chimborazo by several hundred toises, though to the present 
day it has been considered as the most elevated point of the new continent. 
The great chain of the Peruvian Andes divides itself, between the 14th and 
20th degree of south latitude, into two longitudinal branches. These two branches 
are separated from one another by a great valley, or rather by a plateau, whose 
surface is elevated 2033 toises above the level of the sea, and whose northern ex- 
tremity comprises the lake of Titicaca. The shores and the islands of this lake 
are remarkable as for having been the seat of the ancient civilization of Peru, and 
the central point of the empire of the Incas. The western chain separates the 
~ bed of the lake of Titicaca, and the valley of Desaguadero forms the coast of the 
southern ocean, and presents a great number of volcanoes in actual activity. Its _ 
geognostic constitution is essentially volcanic, whilst the eastern chain is entirely 
formed of secondary and transition mountains of mica slate, of syenite, of por- 
phyry, of red sandstone, of red marle containing rock-salt, of gypsum, and small 
formations of oolitic limestone. 
I. Eastern chain of the Andes.—The eastern chain separates the elevated 
plateau or the valley which incloses the lake of Titicaca from the immense plains 
or steps of Chiquitos and Moxos. It thus forms the line of separation between 
the course of the Rio Beni, of the Madeira, and of Paraguay, and the streams of 
water which flow into the lake of Titicaca and into the Desaguadero. A great 
number of torrents which are poured into the Rio Beni bring with them aurife- 
rous sand. One of these rivulets deposited so great a quantity of this sediment, 
that it gave to the little valley of Tipiani, in the district of Larecaja, the name, 
which became so celebrated, of Dorado, or of El] Dorado. From the 14th to the 
17th degree of latitude, the chain attains, without interruption, the inferior limits 
