126 PATAGONIAN EXPEDITIONS: NARRATIVE. 



had made an opening in a burrow at any point, a torrent of water would 

 rush into the subterranean channel, either instantly drowning such of its 

 inhabitants as were caught below, or driving them to seek refuge by escap- 

 ing from the burrow where they were certain to meet with a similar death 

 from the downpour of rain on the outside. As I walked about this morn- 

 ing, considering the destruction wrought by the storm of the previous night, 

 I was struck with the great importance of the work accomplished by rod- 

 ents and other burrowing animals, when considered as agents of erosion, 

 and it appeared to me that this source of erosion had not been given suf- 

 ficient attention in our text-books of geology, when treating of the various 

 erosive agents. 



The storm had rendered the surface of the surrounding country quite 

 unfit for travel, so that we were compelled, not unwillingly, to remain 

 where we were for the day, and indeed there was much of profit to be gained 

 from our sojourn. Mr. Peterson found ample employment throughout the 

 day in caring for the supply of rodents taken in our traps during the night, 

 which had been supplemented by others picked up on my walk in the 

 early morning. Personally I spent the forenoon in examining the bluft' 

 a short distance below camp, where the river had cut a narrow channel 

 through the accumulation of silt and other materials, which had been 

 brought down and deposited by the ancient glacier in such manner as to 

 obstruct the natural course of the river. The materials of the bluff were 

 found to consist for the most part of fine silt. This exhibited splendid 

 examples of a peculiar, complicated, irregular, concentric structure which 

 had been wrought out in high relief by wind erosion, from which I secured 

 the photograph reproduced in Fig. 13. In the afternoon I saddled a 

 horse, in order to find a safe place at which to ford the river with our 

 cart, since the travelling for a considerable distance seemed much better 

 on the opposite side. Having successfully accomplished this purpose, I 

 proceeded to the summit of some high hills that lay at a distance of sev- 

 eral miles to the northwest and formed the divide between the Chico and 

 the Belgrano. From the top of one of the higher of these I secured an 

 excellent view of the surrounding country. Between the western limits 

 of the high basaltic table-land of the interior and the eastern foot-hills of 

 the Andes, there lay a wide tract of open country, well grassed and for the 

 most part free from lava. A few miles farther up I could see that the 

 river forked again. The southernmost of these two branches came from 



