CONSTRUCTION NOTES 265 



depth of six to eight inches below the finished grade of the walk at the side 

 of the walk. On this subgrade a layer of slag or crushed stone (to pass a 

 2 or 2^2-inch screen) should be put in place, thoroughly tamped or rolled, 

 leaving the surface at a grade parallel with and one and one-half inches 

 below the proposed finished grade of the walk. On the surface thus pre- 

 pared a layer of pit gravel (much preferable to washed gravel because of 

 the clay content) should be spread, thoroughly watered and tamped or 

 rolled to a depth of one and one-half inches. If it is necessary to use fine 

 washed gravel, then approximately 15 per cent of limestone dust (not 

 screenings) should be incorporated into this gravel wearing surface to bind 

 the surface. The gravel used for this wearing surface should pass a one- 

 half-inch screen. It is much preferable to construct permanent gravel 

 walks in this way; because if gravel is used for the foundation course the 

 condition of the walk during the wet months of the spring and late fall 

 become extremely soft unless this gravel has been thoroughly screened, 

 excluding all particles which pass a three-fourths-inch screen. 



(ai) Cobblestone or medina block walks on cinder foundation (foundation 

 course and wearing surface}. Cobblestone and medina block pavements 

 when used for the average walk are usually laid on a sand cushion base 

 with a cinder foundation and are seldom laid on a concrete foundation. 

 Walks of this character should be subgraded to allow at the side of the walk 

 for a depth of six inches of cinders plus a two-inch cushion of sand and the 

 thickness of the cobblestones or medina block. It is quite necessary in this 

 type of walk construction to lay the cobblestones or medina blocks firmly 

 in the sand cushion, leaving an even surface on the top of the walk, and 

 thoroughly to fill the voids between the stones with fine sand. See also \ab. 



(b) Tanbark walks (foundation course and wearing surface}. Tanbark 

 walks differ from gravel walks only in the method of surfacing, except 

 where a tanbark walk is developed as a woodland trail, in which case the 

 foundation of the walk is constructed in accordance with the notes for 

 woodland trails. On the surface of the gravel walk completed in accordance 

 with previous notes under Gravel Walks a layer of tanbark not exceeding 

 one-half inch in thickness should be carefully spread, watered and rolled. 

 It is quite essential to bear in mind that tanbark walks, because of the 

 loose texture and lightness of the surfacing material, cannot be constructed 

 in any location or on any grade where the surface of the walk will be exposed 

 to any flow of surface water. 



(ca) Turf walks (foundation course and wearing surface}. Ideal drainage 

 conditions, both surface and subsurface, and a sandy loam soil permanently 

 compacted make for the greatest satisfaction in the construction of turf 

 walks. It is quite essential to install a line of drainage at a depth of not 



