1397) THE SOURCE OF THE TERTIARY MAMMALIA 257 
continent had not appeared, except as a few small islands. North 
America, completely separated from South America, formed a great 
island, with large lakes of brackish water; and this part of South 
America had lost its insular and peninsular form. The Argentine 
Territory had completely emerged, and extended to the east towards 
South Africa, while to the south and west it was prolonged to form 
a large continent, which placed it in connection with Australia and 
New Zealand. 
It was during this epoch in that great southern continent, and 
especially in its central portion now constituting the Argentine 
Territory, that the highest organisms developed, the great class of 
the mammals which immediately spread over the southern lands, 
and subsequently penetrated by different routes into the northern 
hemisphere. 
The great barrier of the Andes was then low, and did not hinder 
the atmospheric currents. The climate was hot and humid, and a 
luxuriant vegetation covered all the Argentine Territory. As far as 
the present Patagonian plains, to-day dry and sterile, there flourished 
large forests of palms and conifers, whose petrified remains fill whole 
deposits, in which one continually finds huge tree trunks trans- 
formed into flint still occupying their natural position and constitut- 
ing dead forests, forests of stone, columns of flint such as that which 
one can see opposite the Museum of La Plata crowned with the bust of 
the unfortunate Crevaux, and which the imagination of the dwellers 
of the Patagonian deserts, on account of the undulation of the land, 
takes to be the masts of petrified ships. 
Alternating with the branches and tree trunks transformed into 
stone, which fill the deposits of sandy rock appearing at various 
points of the Patagonian Territory, large bones are met with 
similarly petrified, belonging to terrestrial vertebrates of the ex- 
tinct group Dinosauria. They were reptiles with an enormously 
thick tail, and the hind limbs much longer and thicker than the 
fore limbs, so that, supporting the body on the hind limbs and tail, 
they could assume a semi-vertical or oblique position resembling 
that of a kangaroo When one says that as a matter of fact they 
could have looked over the roofs of most of the buildings at La 
Plata, one can judge of the truly colossal size which some repre- 
sentatives of this group attained. 
The birds of that time were no less noteworthy than the reptiles. 
They were such as Physornis and Phororhacos, true monsters, bipeds 
with short and thick wings, the claws of an eagle, and the beak of 
1 Of the three sub-orders into which the Dinosauria are divided, namely, Sauropoda, 
Theropoda, and Orthopoda, the characters mentioned above are peculiar to the two last. 
The sub-order of the Sauropoda, to which the gigantic genera of Patagonia, Argyrosaurus 
and Titanosaurus Lyd., belong, have the four limbs more or less equal, or the front pair 
searcely any shorter than the hind pair. 
