.582 PRACTICE OF AGRICULTURE. Part III. 



is (his so material, as ground of this description is capable of containing a great quantity 

 of water without endangering the flooding of the road. In such situations it also 

 fortunately happens that land is seldom of much value, and therefore, in making a road 

 through a morass, a much greater breadth should be included between the lateral drains 

 than where the ground lias an undulating surface. Attention should also be paid to cut 

 the ditches of a moderate depth, as the tenacity of such soils depends upon their being 

 kept in a somewhat ninist state. If a section of such ground be exposed to the sun and 

 air, by deep side cutting, it soon pulverises, and loses its elasticity, when the level of the 

 road falls, and its surface gets into disorder. The drainage of a road should rather be 

 made across than in a lateral direction, as being less apt to be injured by the traffic upon 

 it." (Erf. En eye. art. Roads.) 



3608. The side drains Telford and Walker recommend to be, in every instance, on the 

 field side of the fence. In cases, Telford observes, where a road is made upon ground 

 where there are many springs, it is absolutely necessary to make a number of under and 

 cross drains to collect the water and conduct it into the side drains, which should always be 

 made on the field side of the fences. The orifices of these cross drains should be neatly 

 and substantially finished in masonry. 



3609. The surface-drains, or water-tables, should be made a few inches lower than the 

 side of the road, and of the common width of a spade at the bottom, and they should have 

 frequent cross drains under the path and fence, back into the outer side drain. 



3610. IFater-tables across the road become requisite in some cases, as in flat roads on 

 a steep slope. These should always be made at right angles to the road, with their sides 

 gently sloping, to occasion as little obstruction to carriages as possible. In some few 

 cases, where roads are liable to floods, or are deficient in drainage, these surface-tables 

 may require to be made of a considerable breadth, and paved ; in this case Greig {App. to 

 Strictures on Road Police, p. 219.) directs to lay six feet at the bottom of it flat, and 

 twelve feet on each side to rise at the rate of one inch in the foot, which will make the 

 depth one foot ; and from the size, no carriage will feel any jerk or shake in passing it. 

 The pavement should be made of hammered stones, of nearly equal depth, each stone 

 from nine to twelve inches long on the surface, and four to eight inches broad, and nine 

 inches to a foot deep ; the under-side to be flat in the under-face, and not of an irregular 

 or ancrular under-surface, as in that case it would not be solid. 



3611 . Bridges and embankments, of different degrees of magnitude, are required in all 

 lines of road of any length or variety of surface. The subject of large bridges we leave 

 to the engineers, no department of their art having attained higher perfection ; of which 

 the wonderful erections by Telford, in almost every mountainous district in Britain, may 

 be referred to as proofs. We confine ourselves entirely to such stone arches as may be 

 designed by road-surveyors, and built by country masons. In many cases, cast-iron 

 might be substituted for stone with economy and advantage as to waterway ; but though 

 the principle of constructing both cast and wrought iron bridges is perfectly simple, the 

 execution, and especially the putting up, requires more skill, and are attended with much 

 more risk than the erection of either stone or timber bridges. 



3612. One low arch is in general the most desirable description of common road- 

 bridge. But most of the country bridges, as Clarke observes, consist of several small, 

 high, semicircular arches : where there is a single arch, the stream passes without inter- 

 ruption ; if there are two or three in the same situation, the space through which the 

 water is to pass is necessarily contracted by the width of the piers. Ice, and large bodies 

 carried down by floods, frequently stop up the small arches, and the accumulated water 

 carries away the bridge ; but if such accidents should not happen, the constant currents 

 rushing against those piers wash out the mortar, loosen the stones, and very soon under- 

 mine the work, if not extremely well put together, which is seldom the case. Unless 

 the river or stream is narrow, or the banks very high, a semicircle is an inconvenient 

 shape for an arch ; it has been adopted on account of the insufficiency of the abut- 

 ments, and because the pressure is more perpendicular ; but scientific engineers, in all 

 countries, now construct their bridges with wide openings, and make the arches either 

 semi-ellipses, or segments of large circles — so that the space above the highest floods is 

 comparatively little, and the ascent over the bridge inconsiderable. In country 7 bridges 

 in Ireland, Clarke continues, the foundations are invariably, and often intentionally, 

 defective : the mason considers himself an honest man, if his bridge lasts seven years; 

 whereas, from the durability of materials in that country, it ought to endure for ages. 

 Whatever is under water is out of sight, and is generally composed of loose stones, 

 thrown promiscuously together, on which the masonry is erected, and all the pains 

 and expense are bestowed on the cut-icaters and wings, when the heaviest stones, and 

 those accurately jointed, ought to be laid in the foundations. The greatest attention 

 should be paid to the quality of the materials : the stones should be large, and laid 

 in level courses, in the best mortar, composed of sharp sand, free from loam, and quick- 

 lime, accurately mixed together; the coping of the parapet is generally so slight, that it is 



