354 CHARLES DARWIN 



one might not have walked over backwards, or got off his 

 mule on either side. One of the bad passes, called las 

 Animas (the souls), I had crossed, and did not find out 

 till a day afterwards, that it was one of the awful dangers. 

 No doubt there are many parts in Which, if the mule should 

 stumble, the rider would be hurled down a great precipice; 

 but of this there is little chance. I dare say, in the spring, 

 the " laderas," or roads, which each year are formed anew 

 across the piles of fallen detritus, are very bad; but from 

 what I saw, I suspect the real danger is nothing. With 

 cargo-mules the case is rather different, for the loads pro- 

 ject* so far, that the animals, occasionally running against 

 each other, or against a point of rock, lose their balance, and 

 are thrown down the precipices. In crossing the rivers 

 I can well believe that the difficulty may be very great: at 

 this season there was little trouble, but in the summer they 

 must be very hazardous. I can quite imagine, as Sir F. 

 Head describes, the different expressions of those who have 

 passed the gulf, and those who are passing. I never heard 

 of any man being drowned, but with loaded mules it. fre- 

 quently happens. The arriero tells you to show your mule 

 the best line, and then allow her to cross as she likes: the 

 cargo-mule takes a bad line, and is often lost. 



April 4th.— From the Rio de las Vacas to the Puente del 

 Incas, half a day's journey. As there was pasture for the 

 mules, and geology for me, we bivouacked here for the 

 night.' When one hears of a natural Bridge, one pictures 

 to one's self some deep and narrow ravine, across which a 

 bold mass of rock has fallen; or a great arch hollowed out 

 like the vault of a cavern. Instead of this, the Iricas 

 Bridge consists of a crust of stratified shingle cemented to- 

 gether by the deposits of the neighbouring hot springs. It 

 appears, as if the stream had scooped out a channel on one 

 side, leaving an overhanging ledge, which was met by earth 

 and' stones falling down from the opposite cliff. Certainly 

 an oblique junction, as Would happen in such a case,_ was 

 very distinct on one side. The Bridge of the Incas is by 

 no means worthy of the great monarchs whose name it 

 bears. 



5f/i._We had a long day's ride across the central ridge, 



