RAILWAY CONSTRUCTION. 3 



be found sufficiently long and uniform to permit a practical 

 direct asceat, and the only way out of the difficulty is to 

 make a series of detours along the various spurs of the mountains 

 to gain length to overcome the height. Each detour has to be 

 the subject of most careful study. Forming part of a long series 

 of ascending gradients, it has to follow the winding of the 

 mountain-side, must be laid out to be always gaining in height, 

 and will comprise important works, many of them of considerable 

 extent, necessary for protection against the floods and atmo- 

 spherical changes of the locality. 



In these higher altitudes nature is met with on the grandest 

 and most rugged scale. Deep gorges, wide ravines, and almost 

 perpendicular rocks form the pathway along which the line 

 must be carried, and the skill of the engineer is taxed to the 

 utmost to select a course which shall comprise a minimum of 

 the works of magnitude. Mile after mile of line must be laid 

 out in almost inaccessible places, loose or broken rocks must 

 be avoided, a firm foundation must be obtained at all points 

 skirting high ledges, and ample provision must be made for 

 those mountain torrents which rise so suddenly, and are liable 

 to sweep away all before them. 



Many grand examples of these detour lines are in existence 

 in different parts of the world, and the traveller passing over 

 them can realize the difficulties that had to be encountered, and 

 the masterly manner in which they have been overcome. 



Before proceeding to carry out the works of any line of 

 railway, it is necessary to prepare a complete plan and section 

 of the line, showing the route to be followed and the position 

 of the various curves, gradients, and principal works. Within 

 certain limits, the course of the line may have to be slightly 

 modified as the work proceeds, in consequence of ground turning 

 out unfavourable, river-crossiDgs treacherous, or of sites in- 

 volving so many contingent alterations that it is found better 

 to avoid them altogether. The route should, however, be so 

 carefully studied out before completing the final plan and 

 section, as to leave only minor deviations of line and level to 

 be dealt with in the actual carrying out of the work. 



The promoters of lines in the United Kingdom obtain 

 valuable assistance from the ordnance maps, which give full 

 and reliable information regarding the position of all roads, 

 rivers, and boundaries of counties, parishes, and townlands. In 



