About the middle of April, 1866, the message came, and the work began. Along the dead level of the Platte Valley, through endless reaches of prairie, and behind the meagre shelter of outlying hills, the rails are still falling in place,--a continuous belt of iron out-rolled over black loam and arid sand,--mile after mile, day after day; and with the close of the present year there will stretch an unbroken line of five hundred and twenty miles of rail across the Plains to the foot of the Black Hills. There is no occasion to dilate upon the wonderful systemization of labor which has characterized the work of construction. The public is already well apprised of the details, from the pens of industrious and graphic newspaper correspondents. The company itself has been by no means laggard in celebrating its enterprise. Excursion parties of capitalists, editors, and Congressmen have severally given in their testimony; but, after all, the one fact that in less than twenty months American energy has brought the Rocky Mountains within two and one half days' journey of New York--though the distance is two thousand miles--tells the whole story. One of the chief difficulties of this Nebraska route has been, as we have intimated, the scarcity of suitable material for cross-ties, and of fuel for the engines. The employment of Burnetized cottonwood, and the discovery of a very considerable quantity of cedar in the interior, have, however, effectually solved one phase of this problem; while for the production of steam science now offers petroleum as a practical substitute for wood and coal. But independently of this, the road has already reached the bituminous beds of the Black Hills, where it will probably find a plentiful supply for its necessities. Water also is obtained in sufficient quantities by digging from ten to twenty feet down, to the sand which filters the waters of the Platte.