HYPSOMETRIC ADDENDA. 205 



Berghaus has applied to the chains of the Andes in Bolivia, 

 the investigation which I published* regarding the proportion, 

 which varies extremely in different mountain-chains, of the 

 mountain ridge (the mean height of the passes), to the high- 

 est summits (or the culminating points). He finds ,f according 

 to Pentland's map, that the mean height of the passes in the 

 eastern chain is 13,505, and in the western chain 14,496 feet. 

 The culminating points are 21,285 and 22,350 feet; consequently 

 the ratio of the height of the ridge to that of the highest sum- 

 mit is, in the eastern chain, as 1 : 1'57, and in the western 

 chain as 1 : 1.54. This ratio, which is, as it were, the mea- 

 sure of the subterranean upheaving force, is very similar to 

 that in the Pyrenees, but very different from the plastic form 

 of the Alps, the mean height of whose passes is far less in 

 comparison with the height of Mont Blanc. In the Pyrenees 

 these ratios are as 1 : T43, and in the Alps as 1 : 2 -09. 



But, according to Fitzroy and Darwin, the height of the 

 Sahama is still surpassed by 848 feet by that of the volcano 

 Aconcagua (south lat. 32 39'), in the north-east of Valpa- 

 raiso in Chili. The officers of the expedition of the Adven- 

 ture and Beagle found, in August 1835, that the Aconcagua 

 was between 23,000 and 23,400 feet in height. If we reckon 

 it at 23,200 feet it is 1776 feet, higher than Chimborazo.J 

 According to more recent calculations, Aconcagua is deter- 

 mined to be 23,906 feet. 



Our knowledge regarding the systems of mountains, which, 

 north of the parallels of 30 and 31, are distinguished as the 

 Rocky Mountains and the Sierra Nevada of California, has 

 been vastly augmented during the last few years in the astro- 

 nomico- geographical, hypsometric, geognostic, and botanical 

 departments, by the excellent works of Charles Fremont, || of 

 Dr. \Vislizenus,^[ and of Lieutenants Abert and Peck.** There 



* Annales des Sciences Naturelles, t. iv. 1825, pp. 225-253. 



\ Berghaus, Zeitschrift fur ErdJcunde, band. ix. s. 322-326. 



J Fitzroy, Voyages of the Adventure and Beagle, 1839, vol. ii. p. 

 481 ; Darwin, Journal of Researches, 1845, pp. 253 and 291. 



Mary Somerville, Physical Geogr., 1849, vol. ii. 425. 



|| Geographical Memoir upon Upper California, an illustration of 

 liis Map of Oregon and California, 1848. 



^f Memoir of a Tour in Northern Mexico, connected with Col. 

 Donipharis Expedition, 1848. 



** Expedition on the Upper Arkansas, 1845, and Examination of 

 Neiv Mexico in 1846 and 1847. 



