OBSERVED DURING THE RORAIMA EXPEDITION. 251 
mentioned), so Venezuela, Guiana, and North Brazil therefore represent tracts which are 
really more or less differentiated from one another in their flora and fauna. 
Now, as the whole of the tract under consideration (that drained by the Orinoco, the 
Amazon, and the intermediate rivers) rises gradually, or, more generally, by step-like 
ascents, from the sea-level оп its east toward the tableland on its west (i. e. the centre 
of the continent), it is, of course, on this tableland that the rivers take their origin. And 
as, owing to the irregularity of the surface of this tableland, and still more that of its 
slope toward the eastern sea, it follows that each of these rivers collects its head-waters 
from unusually widely separated localities, so it often happens that two or more of 
these rivers draw some portion of their head-waters from unusually contiguous localities. 
Thus it is conceivable, and even probable, that any peculiar animal or vegetable forms, 
which may originate at one of these localities which supplies water to very divergent 
river-systems may distribute themselves over very wide areas by passing along the 
courses of the various rivers thence arising. 
It happens that the rock-pillars of the Roraima group, rising some 5000 feet over the 
general level of the tableland, itself at that part some 3000 feet above the level of the 
sea, pour down from their summits streams which go to swell the Orinoco, the Esse- 
quibo, and the Amazon—in other words, the three rivers respectively of Venezuela, 
Guiana, and Brazil. Now, as has been already mentioned, the flora of Roraima is of a 
very remarkably peculiar character. A most interesting question still awaits solution, 
namely, the relation of the flora of Roraima to the floras of Venezuela, Guiana, and 
Brazil. 
No answer, I say, has yet been attempted to this question; nor can I pretend to 
suggest any. Таш, however, able here to offer, as data to be considered in the question, 
some very general account of the flora of Guiana, and а rather more special account 
of the flora of Roraima in its relation to that of Guiana. 
Guiana, as has been said, rises gradually from the east toward the high tableland of 
the interior of the continent. Instead, however, of thus placing ourselves in imagination 
on its sea-coast and looking westward up its gradual slope, let us imagine ourselves on 
the tableland on Roraima, and that we are looking eastward down toward the sea. 
Were such a bird’s-eye view really possible, we should find that the tableland, or savannah, 
as it is there called, is an open treeless country, its elevated surface hardly anywhere level, 
but swelling up in many hills, and even into some mountain-ranges. We find that only 
along the courses of the rivers, or in the other lower parts where water has accumulated 
in some form, are there more or less extensive belts of trees, and that, on the savannah 
itself, even these trees are, considering that we are in the tropics, of no great size. 
Further eastward, on the lower part of the slope toward the sea, where the rivers 
have already grown wider and approached each other more nearly, the trees are more 
numerous and larger. Still further eastward, lower down the slope, the belts of 
trees, each pertaining to its own river, have widened with the rivers, till they have 
approached and then joined each other; here the trees are of yet larger size. At last, 
at the bottom of the slope, between its foot and the still far distant sea-waves, the wide 
7. 202 
