J30 S. CRUZ, PATAGONIA. [CHAP. & 



small animals. The guanaco is also in its proper district ; herds of fifty 

 or a hundred were common ; and, as I have stated, we saw one which 

 must have contained at least five hundred. The puma, with the condor 

 and other carrion-hawks in its train, follows and preys upon these 

 animals. ' The footsteps of the puma were to be seen almost every- 

 where on the banks of the river ; and the remains of several guanacos, 

 with their necks dislocated and bones broken, showed how they had 

 met their death. 



April 24//z. Like the navigators of old when approaching an unknown 

 land, we examined and watched for the most trivial sign of a change. 

 The drifted trunk of a tree, or a boulder of primitive rock, was hailed 

 with joy, as if we had seen a forest growing on the flanks of the Cordil- 

 lera. The top, however, of a heavy bank of clouds, which remained 

 almost constantly in one position, was the most promising sign, and 

 eventually turned out a true harbinger. At first the clouds were mis- 

 taken for the mountains themselves, instead of the masses of vapour 

 condensed by their icy summits. 



April 2,6th. We this day met with a marked change in the geolo- 

 gical structure of the plains. From the first starting I had carefully 

 examined the gravel in the river, and for the two last days had noticed 

 the presence of a few small pebbles of a very cellular basalt. These 

 gradually increased in number and in size, but none were as large as a 

 man's head. This morning, however, pebbles of the same rock, but 

 more compact, suddenly became abundant, and in the course of half an 

 hour we saw, at the distance of five or six miles, the angular edge of a 

 great basaltic platform. When we arrived at its base we found the 

 stream bubbling among the fallen blocks. For the next twenty-eight 

 miles the river-course was encumbered with these basaltic masses. 

 Above that limit immense fragments of primitive rocks, derived from 

 the surrounding boulder-formation, were equally numerous. None of 

 the fragments of any considerable size had been washed more than 

 three or four miles down the river below their parent-source : consider- 

 ing the singular rapidity of the great body of water in the Santa Cruz, 

 and that no still reaches occur in any part, this example is a most 

 striking one, of the inefficiency of rivers in transporting even moderately 

 sized fragments. 



The basalt is only lava, which has flowed beneath the sea ; but the 

 eruptions must have been on the grandest scale. At the point where 

 we first met this formation it was one hundred and twenty feet in thick- 

 ness ; following up the river course, the surface imperceptibly rose and 

 the mass became thicker, so that at forty miles above the first station it 

 was three hundred and twenty feet thick. What the thickness may be 

 close to the Cordillera, I have no means of knowing, but the platform 

 there attains a height of about three thonsand feet above the level ot 

 the sea : We must therefore look to the mountains of that great chain 

 for its source ; and worthy of such a source are streams that have 

 flowed over the gently inclined bed of the sea to a distance of one 

 hundred miles. At the first glance of the basaltic cliffs on the opposite 

 sides of the valley, it was evident that the strata once were united. 



