legs, which in plan form a rectangle.
The legs are composed of a series of wrought-iron six-segment columns, in lengths of 25 feet, connections being made by cast-iron joint-boxes having tenons on each end running into the column.
The columns have an exterior diameter, including flanges, of 16 inches.
The mountain-chain will be crossed at an altitude of 15,000 feet by a tunnel 3,000 feet in length.
The grades are the steepest known on any ordinary railway.
The workmen employed are Cholos Indians, the only operatives who can endure for a prolonged period the rarified atmosphere at this great elevation.
The subject, after this slight historical general sketch, will be considered under the headings which naturally suggest themselves, founded upon the differences in material, construction, and purpose.
See under their respective heads: —