NOTICE OF THE MEGATHERIUM. 
19 
§ 5. GEOLOGICAL AGE. 
South America is the metropolis of the Edentates. It now contains nearly three times 
as many species as are found in all the other continents. They are here represented by the 
three families of Sloths, Ant-eaters, and Armadillos. The Sloths are peculiar to the region 
between Honduras and Rio Janeiro. Their distribution in ancient times, when their gigantic 
predecessors — the Megatheroids — walked the earth, was far more extensive, reaching from 
Virginia to Patagonia. The Pampas, where remains of the great fossil noticed in our sketch 
have been chiefly found, are vast plains, 1,500,000 square miles in area, stretching from Terra 
del Fuego to the Mountains of Brazil. Palms grow at one end, while snow covers the other 
almost all the year round. Generally speaking, it is the most barren tract in South America. 
In Patagonia it is an almost unbroken sheet of shingle and basalt rocks, diversified with huge 
boulders. In Buenos Ayres it is nearly as level as the sea, interrupted only at vast distances 
by the solitary Umbir. With the exception of this single tree, and the Palm and Orange 
groves on the banks of the La Plata, the chief vegetation is long wire-grass and thistles. 
Having, been exempt, by reason of their warmer latitude, from the floating ice which, at a 
prior period, covered wir.h gravel and boulders the then submerged plains of Patagonia, this 
Pampa does not offer to the eye a single pebble over a surface of hundreds of miles in length. 
Numerous salt lakes alone occupy depressions in the surface of the alluvium. The soil is almost 
wholly a dull reddish, slightly indurated, argillaceous earth, with here and there calcareous 
concretions. Underneath are beds of stratified gravel or conglomerate. These deposits con- 
stitute the Pampean formation, which varies in depth from 20 to 100 feet. They were slowly 
and quietly formed at a time when the Atlantic Ocean, — exceeding its present boundaries, — 
reached far westward to the foot of the central mountain chain, down whose flanks the smaller 
streams and rivers brought the detritus, and spread it beneath the waters in level layers at 
some distance from the shore. The carcasses of animals existing in the country floated down 
upon the same streams, and, reaching the still water of the sea, sank down to their muddy bed. 
The whole area has since been elevated ; the estuary mud of former rivers has been converted 
into wide and level plains, and the shores and submarine batiks of a former sea now form low 
headlands along the present shore* There is no considerable superficial erosion, as would 
have been seen had the upheaval been a violent one, and accompanied with powerful marine 
currents. Most of the Mollusca, barnacles and corals discovered in this deposit are still living 
in the contiguous ocean, — a proof that the formation has been correctly referred to the pleis- 
tocene period. It is in this recent formation, a perfect hecatomb of monsters of extinct races, 
that the Megatherium has been found entombed. The remains are found almost exclusively 
in the cliffs and steep banks of rivers, yet at all depths from the top to the bottom of the 
deposit. 
Most of the bones are in a soft and friable condition, and, like the shells in the same 
deposit, do not emit when burnt an animal odor. Many of them have been broken, abraded 
* This elevation, however, was interrupted by several poriods of rest, as may be inferred from the plains 
cliffs, and lines of sand-dunes existing at different heights. The beds now stand from lfrto 20 feet above the 
level of high water. 
