COMPARISON OF VARIOUS COVERINGS. 295 



Gravel upon a paved foundation, 1 



Broken stone upon a paved foundation, . . . .1.65 

 Broken stone upon earth, ...... 1.70 



Broken stone roads are designated, respectively, those having 

 paved foundations, Telford, and those laid upon earth McAdam 

 roads. 



For general traffic, the Telford road is undoubtedly the most 

 durable, and can be maintained in high condition, at less cost, 

 than any other. The foundation is permanent, and, with a 

 proper depth of materials perfectly consolidated, the whole will 

 always remain intact, except from the wear upon the surface. 



The macadam way is more liable to be broken up from the 

 yielding of the earth foundation on which the materials rest, 

 thus subjecting them to a tendency to motion among themselves 

 under heavy pressures. Any uneasiness of the fragments causes 

 the soil to work upward, so as to help loosen their bonds ; there- 

 fore the wear would not be confined to the surface, and the 

 necessity of replacing them would be more frequent. 



Gravel upon a paved foundation, thoroughly consolidated be- 

 fore use, doubtless makes the best and least expensive of really 

 good roads for light carriages. They are well adapted to local- 

 ities where there is but little heavy traffic, and can probably be 

 kept in repair, in such situations, with as little cost as any other. 



According to a statement made in the " Engineering and 

 Mining Journal," by Mr. Grant, before quoted, a sample road 

 made in Central Park in this way, remained in perfectly good 

 condition, after nearly five years constant use, during all of 

 which time it has required no repairs, except at a point where 

 the gravel became loosened and uneven by the turning of car- 

 riages about a short curve. 



Roads made of gravel on earth foundations are less fitted for 

 general travel than any of those mentioned, and though cheaply 

 constructed are the least useful and most expensive in the long 

 run, requiring a frequent renewal, or constant patching of the 

 covering, to keep them in tolerable order. 



Earth roads made and repaired with plough and scraper are 

 hardly worthy of mention except as temporary expedients in new 

 settlements, though they are not uncommon in the oldest parts 

 of the country. 



