BURIED CITY OF TAKLA-MAKAN 805 
depth of seven or eight inches. We always aimed 
therefore to keep as much as possible along the crests of 
the dunes ; there the animals only sank in half an inch 
or less. 
The davans previously mentioned consist of innumerable 
sand-dunes heaped together one on the top of the other, 
and appear to stretch across the entire breadth of the 
desert. Each davan, with its accompanying depression, 
has a breadth of about a mile and a quarter. A secdon 
of the whole in profile would give an undulating, denticu- 
lated line, the denticulations being the sand-dunes and 
the undulations the greater upswellings of the surface. 
The latter are probably due to the original contours of the 
desert, such as they existed prior to the irruption of the 
sand. In this part of the desert the great upswellings 
run north and south. Hence it is not improbable, that 
they have been determined by the courses of ancient 
rivers, or that the sand has accumulated along the strips 
of land that were never inundated by the rivers when 
they changed their beds. 
