594 Structure of the Cordillera. paetu. 



to the upheavernent of the Cumbre chain, that of 

 Uspallata was formed and elevated ; and afterwards, I 

 may add, in the plain of Uspallata, beds of sand and 

 gravel were violently upthrown. The manner in which 

 the various kinds of porphyries and andesites have been 

 injected one into the other, and in which the infinitely 

 numerous dikes of various composition intersect each 

 other, plainly show that the stratified crust has been 

 stretched and yielded many times over the same points. 

 With respect to the age of the axes of elevation between 

 the Pacific and the Cordillera, I know little : but there 

 are some lines which must — namely, those running 

 north and south in Chiloe, those eight or nine east and 

 west, parallel, far-extended, most symmetrical uniclinal 

 lines at P. Eumena, and the short NW.-SE. and NE.- 

 SW. lines at Concepcion — have been upheaved long 

 after the formation of the Cordillera. Even during the 

 earthquake of 1835, when the linear north and south 

 islet of St. Mary was uplifted several feet above the 

 surrounding area, we perhaps see one feeble step in the 

 formation of a subordinate mountain-axis. In some 

 cases, moreover, for instance, near the baths of Cauquenes, 

 I was forcibly struck with the small size of the breaches 

 cut through the exterior mountain-ranges, compared 

 with the size of the same valleys higher up where enter- 

 ing the Cordillera ; and this circumstance appeared 

 to me scarcely explicable, except on the idea of the 

 exterior lines having been subsequently upthrown, and 

 therefore having been exposed to a less amount of denu- 

 dation. From the manner in which the fringes of 

 gravel are prolonged in unbroken slopes up the valleys 

 of the Cordillera, I infer that most of the greater dis- 

 locations took place during the earlier parts of the great 

 elevation in mass : I have, however, elsewhere given a 

 case, and M. de Tschudi l has given another, of a ridge 

 1 * Eeise in Peru,' Band 2. S. 8 : — Author's Journal, 2nd edit. p. 359. 



