HYPSOMETRIC ADDENDA. 279 



western chain 13602 French, or 14896 English feet. The 

 culminating points are 19972 and 20971 French, 21286 

 and 22350 English feet; consequently the ratio of the 

 height of the ridge to that of the culminating point is, in 

 the eastern chain, as 1 : 1.57, and in the western chain as 

 1 : 1.54. (Berghaus, Zeitschrift fur Erdkunde, Band. ix. 

 S. 322-326). This ratio, which is, as it were, the mea- 

 sure of the subterranean elevating force, is very similar to 

 that which exists in the Pyrenees, but very different from 

 the Alps, where the mean height of the passes is less as 

 compared with Mont Blanc. The ratios are, in the 

 Pyrenees, =1 : 1.43, and in the Alps, =1 : 2.09. 



But, according to Fitz Roy and Darwin, the height of the 



Sahama is still surpassed by 796 French, or 850 English 



feet, by that of the volcano of Aconcagua, on the north east 



of Valparaiso, in Chili, in S. lat. 32 39'. The officers of 



the Adventure and Beagle, in Fitz Roy's Expedition, found, 



in August 1835, the summit of Acongagua between 23000 



and 23400 English feet. If we take it at 23200 (equal to 



21767 Paris feet), this volcano would be 1667 French, or 



1777 English, feet higher than the Chimborazo. (Fitz 



Roy, Voyages of the Adventure and Beagle, 1839, Vol. ii. 



p. 481 ; Darwin, Journal of Researches, 1845, pp. 223 and 



291.) According to more recent calculations, the height of 



Acongagua is given as 22431 French, or 23907 English 



feet. (Mary Somerville, Physical Geogr. 1849, Vol. ii. 



p. 425.) 



Our knowledge of the systems of mountains which, north 

 of the parallels of 30 and 31 N. lat., are called the Rocky 



