STRUCTURAL 127 



in one piece, and are easier to clean. When the 

 deposit of mud accumulates to the level of the 

 outlet pipe, the grating is lifted and the mud 

 raked out. On perfectly level ground, or on a 

 steep gradient gullies should be set 100 ft. apart. 

 On a gentle slope 300 ft. is sufficient, and as far 

 as possible they should occur in clusters to facili- 

 tate the disposal of the water. 



Carriage drives are merely walks on a larger 

 scale. For a single carriage 10 ft. is wide enough, 



DIAGRAM 46. 



but unless the drive is very short this has a mean 

 appearance. A width of 14 ft. will just allow 

 two vehicles to pass each other, and 16 ft. is a 

 better allowance. Whatever the gradient of the 

 ground the formation of the drive looked at as a 

 transverse section should be as though the ground 

 were horizontal. The necessary changes of level 

 must be made in adjacent banks. (See Diagram 

 46.) Curved drives should have the outer edge 

 slightly raised above the inner, in the same way 

 that railway lines are laid. For swiftly moving 

 cars this is almost necessary for safety. 



Drives are made of coarser material than 

 garden paths. From 6 to 9 in. of hard core must 



