248 TRAVELS IN AFRICA, 
The period of their arrival in Kahira is as uncertain as that 
of their departure ; for they travel indifferently either in winter 
or furamer. The journey from AlTuan to Sennaar requires 
much lefs time than that from Affiut to Dar-Fur. 
Many obflacles exift to the eredion of any permanent marks 
by which the roads of the defert might be diftinguifhed. Yet 
I have obferved that the people of our caravan, in fuch places 
as afforded ftones for the purpofe, ufed to colIe£t four or five 
large ones, thus raifmg fmall heaps at proper diflances from each 
other. This affords them fome fatisfadion at their return ; but 
in many places, where the fand is loofe and deep, it becomes 
impracticable. They are then obliged to rely on the facility 
acquired by habit, of diftinguifhing the outline and charac- 
teriflic features of certain rocks, as they are perfedlly ignorant 
of the compafs, and very little informed as to the fixed flars. 
Though the names of the conftellations be little known to them, 
yet they diftinguifh fuch as may guide them in their courfe 
during the night. With all thefe aids however their deviations 
from the true line are not infrequent. Three times, in the 
courfe of our journey, the whole caravan was quite at a lofs 
for the road, though fome of the members of it had made ten 
or twelve different journies to and from Dar-Fur. During the 
whole of my route I had reafon to fufped: that the accounts in 
books of travels, which have generated fuch terrific notions of 
the moving fands of Africa, are greatly exaggerated. While 
we remained at Leghea, indeed, a violent gale fprang from the 
North-well:, and raifed a cloud of fand. At that time I placed 
a wooden 
