136 CHARLES DARWIN 



ual convenience in this country. We passed also Areco. 

 The plains appeared level, but were not so in fact; for in 

 various places the horizon was distant. The estancias are 

 here wide apart; for there is little good pasture, owing- to 

 the land being covered by beds either of an acrid clover, 

 or of the great thistle. The latter, well known from the 

 animated description given by Sir F. Head, were at this 

 time of the year two- thirds grown; in some parts they were 

 as high as the horse's back, but in others they had not yet 

 sprung up, and the ground was bare and dusty as on a turn- 

 pike-road. The clumps were of the most brilliant green, and 

 they made a pleasing miniature-likeness of broken forest 

 land. When the thistles are full grown, the great beds are 

 impenetrable, except by a few tracts, as intricate as those 

 in a labyrinth. These are only known to the robbers, who 

 at this season inhabit them, and sally forth at night to rob 

 and cut throats with impunity. Upon asking at a house 

 whether robbers were numerous, I was answered, " The this- 

 tles are not up yet ;" the meaning of which reply was not at 

 first very obvious. There is little interest in passing over 

 these tracts, for they are inhabited by few animals or birds, 

 excepting the bizcacha and its friend the little owl. 



The bizcacha 1 is well known to form a prominent feature 

 in the zoology of the Pampas. It is found as far south as 

 the Rio Negro, in lat. 41, but not beyond. It cannot, like 

 the agouti, subsist on the gravelly and desert plains of Pata- 

 gonia, but prefers a clayey or sandy soil, which produces a 

 different and more abundant vegetation. Near Mendoza, at 

 the foot of the Cordillera, it occurs in close neighbourhood 

 with the allied alpine species. It is a very curious circum- 

 stance in its geographical distribution, that it has never been 

 seen, fortunately for the inhabitants of Banda Oriental, to 

 the eastward of the river Uruguay : yet in this province there 

 are plains which appear admirably adapted to its habits. 

 The Uruguay has formed an insuperable obstacle to its 

 migration: although the broader barrier of the Parana has 

 been passed, and the bizcacha is common in Entre Rios, the 



*The bizcacha (Lagostomus trichodactylus) somewhat resembles a large 

 rabbit, but with bigger gnawing teeth and a long tail; it has, however, only 

 three toes behind, like the agouti. During the last three or four years the 

 kins of these animals have been sent to England for the sake of the fur. 



