. A manual of the principles and practice of road-making : comprising the location, consruction, and improvement of roads (common, macadam, paved, plank, etc.) and railroads . k- direction, as AEB, itwouldincrease the depth andwidth to be filled up, as isshown by the correspond-ing profiles. But sometimes the two Asides of the valley ap-proach each other at somepoint lower down, so asto render the space be-tween their banks narrow-er though deeper; and ifon measurement this areais found on the whole to be lessened, so as to require lessembankment, the road should cross at that point insteadof
. A manual of the principles and practice of road-making : comprising the location, consruction, and improvement of roads (common, macadam, paved, plank, etc.) and railroads . k- direction, as AEB, itwouldincrease the depth andwidth to be filled up, as isshown by the correspond-ing profiles. But sometimes the two Asides of the valley ap-proach each other at somepoint lower down, so asto render the space be-tween their banks narrow-er though deeper; and ifon measurement this areais found on the whole to be lessened, so as to require lessembankment, the road should cross at that point insteadof higher up. Another case in F?- 29- which a valley may,with advantage, becrossed down stream,is when in that partof the valley are founddetached or isolatedhills and ridges, as Eand F, which maycause a great savingof embankment, onthe fine AEFB, com-pared with either thestraight route ACB, or the up-stream one ADB, as isshown in the accompanying plan and profile, in which thesame letters refer to corresponding lines. When a road is to join two places on the opposite sides ^m *^. RECONNAISSANCE. 85 of a ridge, we can profit by the observation that thestreams, by the approach of their sources, show the low-est points of the ridge ; and of the various passes thusindicated, we should choose that one, the valleys of thestreams from which run as nearly as possible in the di-rection of the required line ; and that one, also, whichhas the most uniform inclination—not easy at the footand steep towards its summit, as is often the case. When a road is to join two places situated on the sameside of a mountain ridge, hut half way down its side, astraight line between them would cross, in their deepest andwidest parts, all the principal valleys which run downfrom every gap. One of two other plans must then beadopted ; either to ascend, and carry the road, with neces-sary windings, at the level of the culminating points ofthe gap, where the valleys have only begun to be hollowedout; or to ca
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Keywords: ., bookcentury1800, bookdecade1850, booksubjectrailroa, bookyear1853
