National Geographic : 1906 Oct
584 THE NATIONAL GEOGRAPHIC MAGAZINE First and Second Courses of Wood Covered with Lump Clay Pile of Wood and Clay Completed and Firing Begun in One of the Flues Burning the Roads, Clarksdale Mississipi. -After the road has been ploughed as deep as a four-horse team can drag the plough, the clay is heaped in furrows and then pieces of wood laid across the ridges. Alternate layers of clay and wood are built on this foundation. Photos from Office of Public Roads.