Of course, if the country has a sharp contour, the ordinary difficulties of line-construction multiply very rapidly. The great cuttings through the hills may have to be carved out of resisting rock, a work that is carried on through many levels, known to the engineers as ledges or as benches. If there are high hills to be notched there will probably be great hollows where the circumstances do not justify carrying the line on bridge or trestle. In these cases come the fills, or embankments. We have already shown how the locating engineer in the first instance has tried to plan his line so that the earth or rock from his cutting will be as nearly as possible sufficient to form the near-by embankments. Sometimes it is not, and then the resident engineers must locate borrow-pits, where the hungry demand of the railroad for dirt will cause a great hollow to show itself on the face of the earth. The borrow-pit must be carefully located--convenient of access, far enough from the track not to be a danger spot to it. This is one of the infinity of problems that come to the construction engineer. For these big jobs laborers' camps will be established close to them; and small temporary railroads peopled with hordes of restless dummy-engines and forcing their narrow-gauged rails here and there and everywhere, will be busy for long weeks and months. There will not be much hand-cutting in the ledges. Steam shovels, mounted like locomotives upon the rails, and pushing forward all the while, will fairly eat out the hillside. One of these will catch up in a single dip of his giant arm more than a wagon load of soft earth or of rock that has been blasted apart for his coming. To make the fills the engineers must often build rough wooden trestles out of the permanent level of the line. The dummy-engines, with their trails of dump-cars, coming from the back of the steam shovels in the cutting, or from the nearest borrow-pit, will hardly seem in a single day to make an appreciable effect upon the fill. But the days and weeks together count, and the dumping multiplies until the rough trestle has completely disappeared, and the railroad has a firm and permanent path across the edge of the dizzy embankment. And these embankments can be made truly dizzy. The passenger going west from Omaha on the new Lane cut-off of the Union Pacific finds his path for almost twenty miles through deep cuttings of the crests of the rolling Nebraska hills, across the edge of the long fills over wide valleys. The Lackawanna railroad building a great cut-off on its main line where it passes through New Jersey has just finished the largest railroad embankment ever built--an earthen structure for two tracks, three miles long and seventy-five to one hundred and ten feet in height. [Illustration: CUTTING A PATH FOR THE RAILROAD THROUGH THE CREST OF THE HIGH HILLS] [Illustration: A GIANT FILL--IN THE MAKING] [Illustration: THE FINISHING TOUCHES TO THE TRACK]