262 ANALYSIS OF THE MAPS 
vans lightly laden. An hour's march of a lightly laden 
caravan seldom exceeds two geographical miles three- 
tenths, and that of a numerous caravan heavily laden does 
not exceed a mile and a half, or a mile and three quar- 
ters*. 
On quitting Djenne, M. Caillie travelled by water. 
The current of the river was slow, the obstacles arising 
from the faulty construction of the vessel, the ignorance 
and unskilfulness of the pilot, and the islands and sand- 
banks, reduce an hour's direct navigation to two English 
miles. Different causes producing, however, similar 
results determine the same value for an hour's march 
in the deserts between Timbuctoo and Fez. This number 
of two miles taken as an average for a long journeyf 
admits of almost all possible differences in the degree of 
expedition with which a caravan will move at different 
times : while it forms also the intermediate length between 
the progress of a caravan heavily and of one moderately 
laden, which was the case with the caravans which M. 
Caillie accompanied from Timbuctoo, as may be seen by 
his narrative. 
This same deficiency of space with a variation in 
the bearings, has caused the frequent breaks which I 
* See below. Art. 3, remarks on the extent of an hour's and a day's 
journey in Northern Africa. 
t Ninety-six days exclusive of those of rest. 
