392 



PASSAGE OF CORDILLERA. March^ 1835. 



action), I was astonished to find perfectly rounded masses 

 of the black calcareous clay-slate with organic remains, — the 

 same rock which I had just crossed in situ on the Peuquenes. 

 These phenomena compel us to arrive at the following con- 

 clusion : — that the Peuquenes existed as dry land for a long 

 period anterior to the formation of the second range, and 

 that, during this period, immense quantities of shingle were 

 accumulated at its submarine flank. The action of a dis- 

 turbing force then commenced : these more modern deposits 

 were injected by dikes, altered by heat, and tilted towards 

 the line whence, in the form of sediment and pebbles, they 

 had originally proceeded, — thus making the ofi'spring at first 

 appear older than its parent. This second, grand, and sub- 

 sequent line of elevation is parallel to the first and more 

 ancient one. 



I will only make one other geological observation: the 

 Portillo chain in the neighbourhood of the pass is rather 

 more elevated than the Peuquenes, yet the waters of the 

 intermediate district have burst a passage through it. On 

 the supposition of a subsequent and gradual elevation of the 

 second line, this can be understood ; for a chain of islets 

 would at first appear, and as these were lifted up, the tides 

 would always be working out deeper and broader channels 

 between them. At the present day, even in the most retired 

 sounds on the southern coast, the currents in the transverse 

 breaks which connect the longitudinal channels, is so strong, 

 that I have heard of one instance where a small vessel under 

 sail was whirled round and round. 



Mr. Pentland,* when describing an hydrographical phe- 

 nomenon of a nearly similar kind, but on an infinitely 

 grander scale, which occurs in Bolivia, says, ^^This very 

 curious fact, of rivers escaping through such an immense 

 mountain-mass as the Bolivian Cordillera, is perhaps one of 

 the most important points connected with the physical 

 geography of this portion of the Andes, and deserves to be 



* Journal of the Royal Geograph. Society for 1835. 



