ROADS. 
363 
m 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 them 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 much 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 durabihty 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 
