The railway to-day is one of the matter-of-fact associations of our active life. We use it so constantly that it requires some little effort to think of it as a wonderful thing; a creation of man's ingenuity, which did not exist when our grandfathers were young. Its long bridges, high viaducts, and dark tunnels may be remarked and remembered by the traveller, but the narrow way of steel, the road itself, seems but a simple work. And yet the problem of location, the determination, foot by foot and mile by mile, of where the line must go, calls in its successful solution for the highest skill of the engineer, whose profession before the railway was created hardly existed at all. Locomotives now climb heights which a few years ago no vehicle on wheels could ascend. The writer, with some engineer friends, was in the mountains of Colorado during the summer of 1887, and saw a train of very intelligent donkeys loaded with ore from the mines, to which no access could be had but by those sure-footed beasts. Within a year one of that party of engineers had located and was building a railway to those very mines. No heights seem too great to-day, no valleys too deep, no cañons too forbidding, no streams too wide; if commerce demands, the engineer will respond and the railways will be built. The location of the line of a railway through difficult country requires the trained judgment of an engineer of special experience, and the most difficult country is not by any means that which might at first be supposed. A line through a narrow pass almost locates itself. But the approach to a summit through rolling country is often a serious problem. The rate of grade must be kept as light as possible, and must never exceed the prescribed maximum. The cuttings and the embankments must be as shallow as they can be made--the quantities of material taken from the excavations should be just about enough to make adjacent embankments. The curves must be few and of light radius--never exceeding an arranged limit. The line must always be kept as direct as these considerations will allow--so that the final location will give the shortest practicable economical distance from point to point. Many a mile of railway over which we travel now at the highest speed has been a weary problem to the engineer of location, and he has often accomplished a really greater success by securing a line which seems to closely fit the country over which it runs without marking itself sharply upon nature's moulding, than if he had with apparent boldness cut deep into the hills and raised embankments and viaducts high over lowlands and valleys. [Illustration: View Down the Blue from Rocky Point, Denver, South Park and Pacific Railroad; showing successive tiers of railway.]