ROADS. 



363 



ill wet, will need no argument to convince them of 

 the total inattention paid to this subject. 



In laying- out roads, attention should be paid not 

 only to levels and distances, but to the nature of 

 the country through which the road is to pass, and 

 the facilities of keeping it in repair ; and, in choos- 

 ing materials for its construction, we are to recol- 

 lect that the stones placed on theni are not only- 

 exposed to friction, but also to the pounding or 

 crushing action of the weights which roll over them ; 

 and, consequently, that a tough as well as hard sub- 

 stance is required. Rocks which are composed of 

 minerals of unequal degrees of toughness are great- 

 ly inferior to those which are of the same texture 

 throughout. It is owing to this circumstance that 

 granite affords roadstones far inferior to those of 

 the trap rocks. In the City of New- York, the gran- 

 ite has latterly been extensively introduced as a 

 paving-stone where the walks intersect the streets; 

 but the slightest attention will show that it is mo^^t 

 rapidly pulverized by the friction to which it is con- 

 stantly exposed from horses and carriages; and 

 not only this, but the kind employed is a coarse and 

 very inferior granite, containing nuich iron ; and we 

 have frequently seen masses of it employed for the 

 above purpose, changed to a brown colour by oxi- 

 dation of the iron for a distance of from five to 

 twelve inches from the surface. Such stones, in 

 such a situation, can last but a short time. De la 

 Beche remarks, that "trappean rocks have lately 

 been imported into London for the purpose of sto- 

 ning some roads ; and no doubt those who have done 

 so will find that, though the trappean stones cost 

 something more in the beginning, they cost less in 

 the end, since their durability is greater than that of 

 the granites." The coarser granites are the most 

 perishable, whether employed for roads or build- 

 ings ; while the finer varieties of the syenite, in 

 which the hornblende prevails and the feldspar is 



