ROADS AND ROAD BUILDING 273 



Block-paved Roads. In block-paved roads the construction 

 is similar to that for brick paving, except that square blocks of 

 wood are used instead of brick. Bois d'Arc and walnut make 

 the most durable material. 



Asphalt Roads. For boulevards and for residence streets 

 asphalt paving is very popular. The surface is carefully graded, 

 rolled, and compacted; and then a layer of concrete several inches 



A street in Paris. 



in thickness is placed on the roadbed; and when this has become 

 thoroughly dry and hard, a heavy layer of pitch-covered pebbles 

 is spread and then a smooth coating of asphalt mixed with fine 

 sand is put on. On both sides of the roadbed the asphalt surface 

 is flanked with gutters and curbstones built up of concrete. 



Oiled Roads. In Southern California roads are often improved 

 by treating them with oil. After the roadbed has been graded, 

 it is plowed up and harrowed. It is then sprinkled with black 

 crude oil. The soil is thoroughly incorporated with the oil by 

 harrowing and by disking. After the oil has soaked into the 

 ground thoroughly, the roadbed is rolled and leveled, and is then 



PRAC. AGRICUL. 18 



