Fig. 363 shows an ordinary crossing made of steel bull-head rails secured in strong cast-iron chairs; and Fig. 364 is a similar crossing made of steel flange rails. In some cases the two rails forming the V are welded together at the point B, and in others they are riveted or bolted together. Fig. 365 shows a diamond or through crossing similar to the one indicated at D, Fig. 359, made of steel bull-head rails and chairs. Crossings are constructed in a variety of forms, whether on the principle of the cast-steel block, or made out of ordinary steel rails; and the above sketches merely illustrate some well-recognized types which experience has proved to be efficient and durable in the road. The angles of the crossings will depend upon the divergence of the intersecting lines to be connected; ordinary crossings, to the angle of 1 in 10, work in for very general use in station-yards, but many are required of angles varying from 1 in 6 to 1 in 14, and in some cases 1 in 16. As a rule, engineers endeavour as far as possible to avoid using ordinary crossings flatter than 1 in 12, or diamond crossings flatter than 1 in 9, because the gap between the running rails becomes very considerable beyond those angles. At the same time, there are many cases of ordinary crossings of 1 in 16, and diamond crossings of 1 in 12 and 1 in 13 laid down in exceptional places, and which have carried heavy and fast traffic for many years. All crossings should be well protected with wing rails and guard rails, as shown on the sketches. Fig. 366 illustrates a method of bringing the UP and down lines of a double line of railway close to each other, and passing them over a single-line opening bridge, or a bridge where the works for the second line have not been completed. This arrangement avoids the necessity of any switches, and prevents any accidents which would arise from a misplaced switch. Each set of trains is effectually kept to its own line of rails. With proper signalling or pilot working, the double-line traffic can be worked over the single-line bridge without difficulty. The writer has adopted the above arrangement in many cases when renewing double-line bridges or viaducts where the width for traffic working has been restricted to half of the bridge. [Illustration: Fig. 361, 362, 363, 364, 365] In some instances the same system has been extended to the carrying of 239 four lines of rails over a double-line bridge, as shown on Fig. 367.