164 REPORT OF THE HARVARD AFRICAN EXPEDITION 
Although small amounts of calcium are found in the laterite-containing soil, 
limestone itself has not been found in Liberia. 
Chemical analyses of the soils have apparently not been made. Linder, 
however, points out that Martin has analyzed soil in Sierra Leone, that is pre- 
dominantly laterite, and has found that its most important constituents are 
Al,0;810, and Fe,O;. 
FLORA 
The tropical temperature, the heavy rainfall, the many rivers, streams and 
marshes, the uneven surface of Liberia, and the nature of the soil (its salinity 
and other mineral and organic constituents), influence the character and dis- 
tribution of the floral types in Liberia more than the altitude. The flora in 
its entirety, although typically West African, has not only certain pecularities 
of its own, but other peculiarities analogous to those of the flora found in Sierra 
Leone and belonging to the botanical subregion styled by Johnston ‘‘Upper 
Guinea.”’ By this term is understood a belt the maximum width of which 
is two hundred and fifty miles, of densely forested country along the West 
African coast, which begins to the south of the river Gambia and extends as 
far east as the country of Dahomey, and is characterized by a heavy rainfall. 
Through settlement and agriculture not only on the coast but in many parts 
of the interior, this primeval forest has given way and has been succeeded by a 
strikingly different flora. It particularly consists of dense scrub and secondary 
growth, with many low, shrubby trees. Owing to all these influences, one finds 
in Liberia a vegetation which varies considerably in the different regions specified. 
Thus, beginning near the coast may be seen either the growth especially as- 
sociated with, and more or less characteristic of, the tropical mangrove swamp, 
or, especially along some of the tidal creeks or rivers, the grasses and vegetation 
of swampy meadows. 
Travelling further inland and passing regions where herbaceous types espe- 
cially prevail, one finds the lower forest of secondary growth, which is very 
characteristic, and which is interspersed in many large areas throughout the 
greater part of the country. In still other more marshy districts, where the 
raffia palm abounds, one finds characteristics of the swampy forest. 
The primeval or virgin rain forest itself, especially characterized by its 
production of the largest trees, is found in areas distant from the villages, and 
in many instances separating territory occupied by different tribes. 
Finally, in parts of the country to the north and eastward the vegetation 
is more like that of the savannas or park-like forest. The characteristics of 
the floral types in these different regions are particularly illustrated in Nos. 
402 to 443, and are so fully described by Dr. Linder in Chapter XXXII, that 
no further reference will be made to them here. 
Mention has already been made of the fact that many of the roots of the 
trees in the forest and in some other parts of the country are either near or on 
the surface. Others do not penetrate to more than a relatively slight depth 
into the deeper layers of the soil. Such a condition is brought about in part 
