The construction and maintenance of a railway calls for the application of so many branches of engineering that several volumes would be required to do ample justice to a subject so comprehensive and ever-extending. To avoid attempting so wide a range, the object of the following pages has been to describe briefly some of the recognized leading features which regulate railway construction, and to assist the explanation with sketches of works selected from actual practice. Where the number of existing good examples is legion, it is somewhat difficult to make a choice for illustration, and the course adopted has been to select such samples of structures as appear best to elucidate in a simple manner the different types of work under consideration. In the drawings and diagrams many important minor details are necessarily omitted, partly to avoid complexity, but principally to leave more prominent the leading features of the particular piece of work referred to in the description. Some of the sketches of the large span bridges and large span roofs are only shown in outline; but, as their principal dimensions are given, a general idea can be obtained of their actual proportions. No allusion is made to the requisite strengths of the various structures described, nor to the necessary dimensions of the materials used in their construction, as this would necessitate the introduction of a vast amount of mathematical formulæ which does not come under the province of the object in view, and which the engineer has already at command from his training and works of reference. Neither is any mention made as to the probable cost of the different works of construction, as these must always vary to a very large extent, according to the locality, facility of supply, and current prices of materials. Every railway scheme which is the outcome of public enterprise has its commercial aspect and influence. The large sums to be invested in its construction are expected to yield permanent and increasing returns, and this desirable end can only be attained where there is thorough efficiency in works and equipment, and a full compliance with those national regulations which control matters connected with public safety. The correct dealing with the technical requirements and structural features of the undertaking must always precede all other considerations, as the constituted authorities will exact a proper fulfilment of all the statutory obligations, regardless of the prospective remuneration to the promoters. A stroke of the pen may change a train-service, or alter the rates and tariffs, but a modification in the works of construction arising out of errors or oversight, would entail a heavy expenditure and tedious delay. The essential point of every railway undertaking must be its suitability and completeness in every respect for the duty for which it is intended.