14 The Naturalist in La Plata. 
is a stretch of sandy soil, or a range of dunes, there 
it is found living ; not seen, but heard; for all day 
long and all night sounds its voice, resonant and 
loud, like a succession of blows from a hammer ; as 
if a company of gnomes were toiling far down 
underfoot, beating on their anvils, first with strong 
measured strokes, then with lighter and faster, and 
with a swing and rhythm as if the little men were 
beating in time to some rude chant unheard above 
the surface. How came these isolated colonies of a 
species so subterranean in habits, and requiring a 
sandy soil to move in, so far from their proper dis- 
trict—that sterile country from which they are 
separated by wide, unsuitable areas? They cannot 
perform long overland journeys like the rat. Perhaps 
the dunes have travelled, carrying their little cattle 
with them. 
Greatest among the carnivores are the two cat- 
monarchs of South America, the jaguar and puma. 
Whatever may be their relative positions elsewhere, 
on the pampas the puma is mightiest, being much 
more abundant and better able to thrive than its 
spotted rival. Versatile in its preying habits, its 
presence on the pampa is not surprising; but pro- 
bably only an extreme abundance of large mammalian 
prey, which has not existed in recent times, could 
have tempted an animal of the river and forest- 
loving habits of the jaguar to colonize this cold, 
treeless, and comparatively waterless desert. There 
are two other important cats. The grass-cat, not 
unlike Felis catus in its robust form and dark colour, 
but a larger, more powerful animal, inexpressibly 
savage in disposition. The second, Felis geoffroyi, 
