268 Mr Buchanan’s Report on the Bridge of Suspension 
construct wholly of iron, to be covered on the top with a coat of 
gravel or road metal, four inches thick : this will soon consoli- 
date, and form a smooth, soft, and permanent footing for the 
horses, and the iron below being preserved by it from the ac- 
tion of the external air, will continue for a long period without 
requiring any renewal or repairs. The gravel is laid upon a se- 
ries of iron-plates, united together into one continued sheet of 
iron, extending quite across, and from end to end of the bridge ; 
these plates again being laid on and firmly supported by a 
strong body of malleable iron frame-work, running every where 
below them. The two footways are raised six inches above the 
carriage way, and are divided from it by a ledging, along which 
there are placed, at convenient intervals, a series of short iron 
posts, to prevent carriages driving on the foot-paths. The foot 
paths, again, are terminated and guarded on the outside, each 
by a strong double railing of iron. The whole roadway, con- 
sisting thus of frame-work, iron plates, railing, and gravel, will 
form, together, a mass of such weight and breadth, and so strong- 
ly bound together in every part, that it will prevent entirely 
that lateral motion to which such bridges are usually subject : 
it will present such a mass of solidity and stiffness, that the 
highest wind will have no effect on it, and even the striking of 
a vessel will do no serious damage, for the bending of the road- 
way, and the yielding of the great mass of chains, will soon ef- 
fectually check the motion of the largest vessel that can ever 
strike here, and that long before the action could have any sen- 
sible effect to move the suspending pillars. But besides that 
motion which takes place in suspended roadways from side to 
side, we must equally guard against any vertical undulation to 
which such a roadway may be subject. This is effected in the 
present bridge, — 1st, By extending under the roadway a series 
of malleable iron-plates, running, longitudinally, from end to 
end. These plates, standing vertically, both support the iron- 
plates above, and give to the roadway a degree of stiffness up 
and down, as the horizontal plates stiffen it from side to side : 
this effect also is greatly aided by the two double side railings 
above it, and which run along the foot-paths. 2d, By binding 
the roadway very firmly to the chains, and binding these latter 
all together into one great mass or cable of chains, so that any 
