1899 | VEGETATION OF TROPICAL AMERICA 5 
doubt has played a conspicuous part in the process; I mean the 
history of evolution of tropical nature. 
All characteristics of a vegetation may be classified into two 
groups of factors, historical and physical. All alterations that the 
climate, the ground, and the surface of a country are passing 
through from time to time must express themselves in the 
vegetable world up to this very day. Consequently this is the 
case with the inner highland of Brazil where Lagoa Santa is 
situated. 
In the first place, Brazil is a primeval country, Geikie’s map? 
showing us that even in paleozoic time, when the firstlings of 
life appeared on the earth, the highlands of Brazil and Guiana 
were raised above the sea level, while the other parts of the 
future South America were still in the keeping of the sea. In 
subsequent geological periods the area of land grew larger. The 
red clay that forms the surface of large parts of the soil is a 
decomposition product of the primitive rock. Also the lime 
rocks, that stick out through the clay here and there in Rio des 
Velhas valley, and in which P. W. Lund’s celebrated caves with 
their fossil remains of extinct species of animals are found, are 
of a primeval limestone without vestiges of fossils. 
Secondly, this highland has, so far as we know, been favored 
by the most excellent tropical climate. Though the ice on the 
highest of South American mountains is said to have been far 
more extensive formerly than now, no glacial period is known 
to have spread its life-killing mantle over the highland of Brazil. 
Then the vegetation developed itself undisturbed through geo- 
logical periods. The species of plants have differentiated, 
fought out their conflicts, accommodated themselves to one 
another, and blended with one another. The vegetation has 
thus had plenty of time, and only when we take this fact into 
consideration shall we get nearer to an understanding of the 
present variety of species. 
How widely different, for instance, are the facts in northern 
Europe! Here we have to do with a comparatively young 
3 Proceedings of the Royal Physical Society of Edinburgh ro. 
