5. As soon as the Act of Parliament has been obtained, the chief engineer directs the immediate construction of a most accurate plan and section of the whole line, from which he ascertains and lays down its gradients. He then determines the sizes of the bridges required, as also the nature and amount of masonry for each; he calculates the quantities of embankments and cuttings, balancing the one against the other as nearly as circumstances will allow, and having, by first boring, and afterwards by the sinking of “trial shafts,” ascertained as accurately as possible the nature of the various strata to be excavated or tunnelled, he proceeds to estimate in detail the cost of the several works, which he then divides into lengths for construction, taking care that in each the amount of earth to be excavated and filled up shall as nearly as possible balance each other; in short, inasmuch as all contractors prudently, and indeed very properly, invariably lower their tenders in proportion as the work they are required to execute has been clearly laid open to their view, and, on the other hand, to secure themselves from unknown difficulties, as invariably _raise_ their tenders for work which has not been sufficiently bored or examined, he is fully sensible that a considerable saving in the cost of the proposed railway will be effected by a clear preliminary development of its works. 6. This mass of information having been prepared, the chief engineer now advertises his work in its various lengths for execution by contract, and, on receiving tenders for the same, he selects, not always the _lowest_, but that which, for various reasons, is the most _approved_, taking security generally to the amount of 10 per cent. of the contract. Previous, however, to the reception of the tenders the chief engineer appoints his staff of assistants. To each 40 or 50 miles there is usually appointed an experienced engineer, having under him “_sub-assistants_” who superintend from 10 to 15 miles each--these sub-assistants being again assisted by “_inspectors_” of masonry, of mining, of earth-work, and of permanent way, to each of whom a particular district is assigned. 7. The chief engineer now finds himself engaged in a new struggle with man in addition to nature. In many instances the contractors let out a portion of the work they have engaged to perform to sub-contractors, who again “set” the earth-work to a body of “navvies,” who again among themselves sub-divide it among the three branches of which their State is composed, namely, “excavators,” “trenchers,” and “runners,” each party of whom appoint their own “ganger.”