336 



FARM DEVELOPMENT 



them into the soil beneath. Seven to 9 inches is as thin 

 as it is usually practicable to make these roads, and 

 for much heavy travel 12 or more inches is necessary. 



Telford roads. Where stone roads are placed on 

 spongy ground, they are sometimes broken by being 

 crushed down into the soft earth beneath. The telford 

 road was designed to better suit this condition. As 

 shown in Figures 215, 216 and 217, the first layer is made 

 up of stones 6 to 12 inches thick, laid with their broad 





Figure 223. Rock crusher with elevator and "screen. The man-size rocks are placed 

 In the hopper, and as they are 'broken the crushed rocks fall into the cups and are carried 

 up to the cylindrical revolving screen. The finer particles fall through the smaller holes, 

 the medium sized crushed stones fall through the larger holes and the larger stones run out 

 at the end of the cylinder. 



surfaces on the bottom and their narrow edges toward 

 the top. These stones must be placed by hand. Be- 

 tween these stones is placed crushed rock, similar to that 

 comprising the lower layer in macadam roads, in suf- 

 ficient quantity to make a covering several inches thick. 

 The next layer and the top layer of fine materials are 

 placed in the same manner as in macadam roads. For 

 a given amount of material used, there is little advan- 



