Among the advantages derived from the substitution of iron rails for wooden rails was the fact that a horse could draw, on the level, heavier loads than before. On the other hand, the heavier the load the greater was the danger in taking the waggons down hill-sides with only a wooden brake to check their speed; and this danger was increased to an even greater degree when the use of iron rails involved the abandonment of the wooden wheels which had hitherto been retained at the back of the waggons in order that the brake should act more effectively. Still further improvements thus became necessary, and these first took the form of inclined planes on which the law of gravity was employed, loaded waggons raising empty ones, or having their own descent regulated, by means of a rope passing round a wheel at the top of the incline. Later on stationary engines and chains were substituted for the wheel and the rope, horses then being employed on the level only. Bailey says on this point: "Waggon ways have generally been so contrived that the ascents were not greater than a single horse could draw a waggon up them; but some cases have happened lately where it required more than one horse, and steam engines have been substituted for horses for drawing waggons up these ascents. At Urpeth waggon way five or six waggons are drawn up at one ascent, by a steam engine placed at the top." Here, then, we have another stage in the process of evolution that was going on. The stationary engine at the top of an incline drawing up, or regulating the descent of, heavier loads, on iron rails, was the first employment on railways of that steam power which was afterwards to develop into the locomotive capable to-day of taking heavy trains at a speed of a mile a minute. In those early days, however, speed was {209}not regarded as a matter of any importance. Colliery managers were quite satisfied with a steady three miles an hour. Although the general conditions of the pioneer railways were, apparently, so primitive, some of the lines were more ambitious and more costly than might, at first, be supposed. Among them were lines from five to ten miles in extent which served the double purpose of (1) enabling collieries in, for example, the Hinterland of the Tyne to benefit from the ever-expanding trade in coal; and (2) providing them with the means of discharging direct into the colliers below Newcastle bridge, thus saving the preliminary transport in, and transshipment from, the coal barges on the river. In these five- or ten-mile distances there were often considerable declivities to overcome, in order that the ideal of a gradual descent should be secured, and the cuttings, embankments, bridges and other works thus carried out were often closely akin to much of the railway construction with which we are familiar to-day. Thus Dr. Stukeley, in his "Itinerarium Curiosum," says in describing the visit he paid to the Tanfield Collieries, Durham, in 1725:--