24 PATAGONIAN EXPEDITIONS: ZOOLOGY. 



Again, at the moraine near the junction of the Rio Belgrano with the 

 Rio Chico, he says (Narrative, p. 123): "The side of the slope, as well 

 as the little plain at its foot, was literally alive with rodents." And then 

 follows a more detailed account (pp. 124, 125) of the species observed, 

 in which special reference is made to the Kerodon and the Tuco-tuco 

 [Ctenomys], quoted in full under these species, and to various unidentified 

 species of mice, as follows : 



" In the small brush which grew at the base and over the slopes of the 

 bluff above our camp, there lived a variety of small rodents for the most 

 part characterized by large, thin ears, delicate soft fur of a bluish brown 

 color above and lighter on the belly, with tails of various length, which in 

 some species might be described as short and in others much attenuated. 



" The tall grass which covered the river valley swarmed with myriads 

 of small rodents somewhat larger than those just mentioned, with usually 

 smaller ears, smaller tails, and a coarser pelage of an almost uniformly 

 dull brown color. While these little animals were present in the greatest 

 abundance they seemed all to pertain to one of two or three different 

 species and exhibited very little variety of either form, size or color." 



A heavy rainstorm made evident the fact that these little animals, 

 especially the burrowing species, are quite an effective geological agent 

 in producing erosion, and also that they suffer at times great destruction 

 from the elements. On these points he says (p. 125) : 



"On walking about the following morning I was much impressed, not 

 only with the amount of erosion which had been effected by the storm, 

 but with the great destruction to animal life of which it had been the cause. 

 Proceeding along the foot of the bluff, I observed a number of dead bodies 

 of the little Cteiwmys magellanica lying about upon the surface, and could 

 only guess at the number of carcasses of these and other rodents that were 

 buried beneath the debris, that during the night had been washed down 

 from the bluff above and now lay at my feet, covering no inconsiderable 

 portion of the surface of the valley to a depth varying from an inch to one 

 or two feet. While the dead bodies of rodents belonging to other species 

 were not wanting, the storm appeared to have been especially destructive 

 to the little tuco-tuco, owing no doubt to the peculiar habit of that animal 

 in burrowing so near the surface of the ground in search of food. When 

 erosion on the surface had made an opening in the burrow at any point, 

 a torrent of water would rush into the subterranean channel, either instantly 



