more than a thousand years before America came into history. But the building of a stone bridge takes time and money-and time and money are scarce in a new land that must expand quickly. So at first the railroad followed the course of the highroad and the postroad, and took the timber bridge unto itself. In some cases it actually fastened itself upon the highroad bridge, as at Trenton, where a faithful wooden structure built by Theodore Burr in 1803 was strengthened and widened in 1848 to take the first through railroad route from New York to Philadelphia. It continued its dual work until 1875. In

Two splendid early examples of this class of monumental construction still remainthe Starucca viaduct upon the Erie Railroad near Susquehanna, Pa., a great structure of seventeen arches and more than a thousand feet long, and an even earlier structure, the stone arch bridge at Relay, Md., built by the engineers of the Baltimore & Ohio Railroad in 1835. Still the timber bridge remained the most available and for the first few years it was used almost exclusively until the ravages of weather and fire demanded a more lasting substitute.

Iron formed that substitute. The first

iron bridge built in the country is believed to have been the one erected by Trumbull in 1840 over the Erie Canal at Frankfort, N. Y. Record is had of one of these bridges being built for the North Adams branch of the Boston & Albany Railroad in 1846. From that time forward the development in this class of bridge was tremendous. Wrought iron gradually superseded cast iron and was in turn superseded by the wonderful fabric of the bridge builder of to-day-steel.

The steel bridge of the truss type-the truss a typically American idea and invention is to-day the most practical of all railroad bridges. The concrete bridge and the permanent stone arch bridge are much more expensive; in most locations plethoric must be the purse of the railroad that can afford these last. The Boston & Albany and the Pennsylvania railroads have afforded them. The last named line owns three splendid specimens of this class of structure at New Brunswick and at Trenton, N. J., and the largest of them all is only a short distance north of Harrisburg, Pa.

With steel bridges the constructing engineer hesitates at no river, no deep valley, no wild ravine, no cleft in the mountain side. He calls the bridge builder to his aid and a feathery trestle appears as if by magic. Across its narrow edge the steel rails follow their resistless path.

BEGINNING CONSTRUCTION

All plans are finished, contracts subdivided and awarded, and in the early spring construction begins upon the new railroad. It will be commenced from as many initial points as possible, these points, of course, being so situated as to be accessible to water communication or to existing railroad lines so that material may be brought with the least delay and expense. As the line goes forward the track follows. This is the ordinary rule through an easy rolling country, where the new railroad popularizes itself from the outset by hiring the nearby farmers and their teams to grade the line through their localities.

Track-laying is much systematized these days, and in this as in so many smaller

undertakings, the machine has supplanted the man as laborer. A real giant is this track-laying machine. It is mounted upon the track and is a form of overhead carrier with a long ove: hang. This carrier is fed with the cross-ties from supply cars just back of the machine and the ties are each dropped close to their appointed place as a locomotive slowly pushes the entire apparatus forward. In a similar way the heavy steel rails are delivered from under the overhang of the carrier. A gang of men makes short work of fastening the rail to the cross-ties and the machine moves steadily forward. It has been known to make a mile a day at this work. The rough uneven track it leaves in its wake is quickly straightened and strengthened. Finally, the ballast is tamped in about the entire structure the ballast, of crushed rock, gravel, cinders or earth as the locality, the wealth of the railroad, or the class of its traffic may demand.

Of course, if the country have a sharper contour, the construction work multiplies its difficulties. There are great cuttings in hillsides to be made the engineers know these as "ledgers"—and there are equally great "fills" where the circumstances do not justify carrying the line on steel bridge. or trestle. For these big jobs laborers' camps will be established and small temporary railroads, peopled with hordes of restless dummy engines, will be busy for long weeks and months. There will not be much hand cutting in the ledges these days. Steam shovels, mounted on rail, pushing forward all the while, will fairly eat out a hillside. They have ravenous appetites, those big fellows, and the engineers will try to have a near-by "fill" ready to use the thousands of cubic yards of earth and rock that come out of the ledge excavations.

To make "fills" the engineers built rough wooden trestles out at the permanent level of the line. The dummy engines, with their trails of dump carts, coming from back of the steam-shovels, will seem at a single time to make hardly an appreciable effect upon the "fill." But the days and weeks 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,

MAKING A TUNNEL

Sometimes the construction engineer brings his new line face to face with a mountain too steep to be easily mounted, and then he prepares to pierce it. Tunnels are not pleasant to ride through. They are, moreover, fearfully expensive to construct and they necessitate a double inspection. But-and the "but" in this case is a very large one-they reduce grades and distances in wholesale fashion, and so in a mountainous country the engi

The ordinary course of such work is by the use of cutting shields proceeding simultaneously from the portals and from the footings of the shafts. These shields are to be likened to steel rings of a circumference only slightly greater than that of the finished tunnel. Men working on different levels of this shield with pick and with drill and dynamite constantly clear a path for it, whereupon it is pressed forward. Tracks follow the cutting shield and more locomotives-steam or electric-are used in removing the material. The use of

neer must be prepared to drive tunnels, and the folk who come after him, to operate them. The tunnel job is apt to be a separate part of the work. It calls for its own expert talent.

If the tunnel is more than a half or threequarters of a mile long, it will probably be dug from a shaft or shafts as well as from its portals. In this way the work will not only be greatly hastened, but the shafts will continue in use after it is completed as vents for the discharge of engine smoke and gases from the tube.

electricity keeps the tunnel quite clear of gases and makes the safest light for the workers.

In rare cases the rock through which the tunnel is bored is strong enough to support itself. But in most cases the engineers prefer to line the bore-with brick as a rule-and this lining is set in place right in the path of the cutting shield. After long weeks and perhaps months of work the time comes when the different bores meet and the tunnel is a single underground tube from portal to portal. After that it

Tunnel boring is the most difficult phase of American railroad construction, doubly difficult when the tunnel is to be carried under some river. Men work in an unnatural environment when they work beneath the surface of the earth and the record of tunnel building is a record of almost countless tragedies. At any instant rock may cease, silt or sand or an underground stream make its unexpected appearance and the helpless workmen find a quick grave. In work where there is the slightest expectation of such a contingency, particularly under rivers, the airlock, with its artificial pressure to hold back the soft earth and moisture, is brought into use. This complicates the work of construction and adds much to the expense. Moreover, it has its own record of tragedies. Still it remains to the infinite credit of a national persistence that there is no record of a tunnel job in the annals of American engineering where the workers have finally given up. Lives have been sacrificed, good-sized fortunes swept away, but in the end the resistless railroad has ever found its underground path.

Culverts have been laid by scores for each small run or hill or creek, the bridge builders along the new line finish their work and cart off their kits, the day comes when there is an unbroken railroad from one end of the new line to the other. It links towns; its localities produce for new markets, commerce from strange quarters pours down upon the land that has known it not. Passengers trains begin regular operation, the fresh-painted depots are fairly brilliant in their newness, the shriek of the locomotive sounds where it has never been heard before.

Life is awakened. The railroad, which is life, has reached out a new arm and creation is begun.

To the operating heads of the great railroad systems to-day rebuilding is far more important than the building of a new line. The country has grown, grown in wealth among other things. The causes that demanded the very greatest economy in the building of early railroad lines no longer exist. The hill that the early engineer

pierced without a second thought. Grades that were once deemed slight are now marked for elimination. The infinite development in the operation of the railroad has seen the grade or the curve become in the course of constant operation a heavy operating expense and something to be done away with.

REBUILDING LINES A NECESSITY

It is all quite as it should be. The early builders did the best that they might do with the opportunities that were theirs. They got the railroad through. It developed wealth, for itself, as well as for the territory it served, and with that wealth it is enabled in these piping days of peace and plenty to correct the alignment errors of the early builders. Moreover, there are frequent cases where the steady increase of traffic has rendered it necessary for a railroad to parallel its trunks with a new line, quite aside from the consideration of grade and curve.

As far back as the early fifties this great work of rebuilding the trunk-line railroads was begun. Certain serious errors in the original alignment of the Baltimore & Ohio Railroad between Baltimore and the Potomac River were corrected at a considerable expense. As time went on other railroads continued this correction work. The fact remains that the greater part of it has been done in the past six or eight years. It is still being prosecuted east and west of the Mississippi. Ten million dollars or fifty million dollars looks like a lot of money to the stockholders of any company when their president tells them that this is to be the cost of this new relief line, this reconstruction, that cut-off; but what is a million dollars when it is going to save more than a hundred thousand dollars a year in the operation of a railroad? It is the far-sighted view of the situation that the railroads nowadays are taking of this reconstruction work.

Mr. Harriman with his transcontinentals from the Mississippi watersheds west, was one of the first pioneers in this work of wholesale reconstruction. The wholesale operating benefits that have resulted from it in the case of his group of Pacifics have been largely responsible for his pre-emi