xvi INTRODUCTION. 
tioned on the subject, and who come frequently to Lagos, 
and other places on the Coast of Guinea, with slaves, deny 
that they meet on their journey with any mountains, and 
that the only difficulties and obstructions arise from the 
frequent rivers, lakes, and swamps which they have. to 
cross. But admitting that such a chain did exist, and 
that it was one solid, unbroken range of primitive gra- 
nite, it would be, even in that singular case, the only in- 
stance, perhaps, of such an extended barrier resisting the 
passage of an accumulated mass of waters. Even the Him- 
malaya, the largest and probably the loftiest range in either 
the New or Old World, has not been able to oppose an 
effectual barrier to the southern streams of 'Tartary. The 
main branch of the Ganges, it is true, does not, as was once 
supposed, pervade it, but the Buramputra, the Sutle) and 
the Indus, have forced their way through this immense 
granite chain. The rocky mountains of America have 
opened a gate for the passage of the Missouri; and the 
Delaware, the Susquehanna and the Potomac have forced 
their way through the Alleghenny range. ‘This objection, 
then, may fairly be said to fall to the ground. 
The objection to the length of its course is somewhat more 
serious, but not so formidable as at first it may appear. 
The great difficulty, perhaps the only one that suggests 
itself, arises from the vast height which the source of a 
river must necessarily be above the level of the sea, in 
order to admit of its waters being carried over, a space 
of 4000 miles; and from the certainty that Park, (who, 
it must be observed, however, measured nothing) passed 
no mountains of extraordinray height to get at the 
Niger. A critic, ina popular journal, whose arguments 
