The first of the changes we were so unwilling to accept was that from wood to iron; the other was that from paddle to screw. Even so late as the end of the decade 1860-70, while all the world else was building ships of iron, propelled by screws, some of which were driven by compound engines, our last remaining great company, the Pacific Mail, put afloat four magnificent failures (from the commercial point of view), differing scarcely in any point, except in size, from those of 1850-56. They were of wood, and had the typically national over-head beam engine. They were most comfortable and luxurious boats; but the sending them into the battle of commerce at such a date, was like pitting the old wooden three-decker with her sixty-four pounders against the active steel cruiser of to-day and her modern guns. Many of the iron screws built at the same time are still in active service; but the fine old China, America, Alaska, and Japan are long since gone, and with them much of the company’s success and fortune. Of course, one great reason for this non-acceptance was the fact that, with us, wood for ship-building was still plentiful, and that it was cheaper so to build than to build in iron, to which material English builders were driven by an exact reversal of these conditions; and the retention of the paddle over the screw was due in a certain degree to the more frequent necessity of repair of wooden screw ships, to which it is not possible to give the necessary structural strength at the stern to withstand successfully the jarring action of the screw at high speeds. The part in advancing the British commercial fleet played by the abrogation of the navigation laws, in 1849, which had their birth in the time of Cromwell (and to which we have held with such tenacity, as ours were modelled upon theirs), need only be barely mentioned. British ship-owners were in despair at the change, and many sold off their ship property to avoid what they expected to be the ruin of the shipping trade, but the change was only to remove the fetters which they had worn so long that they did not know them as such. But the great and overwhelming cause, to which the effect of our navigation laws were even secondary, was the opening up of the vast region lying west of the earlier formed States; the building of our gigantic system of railways; the exploitation, in a word, of the great interior domain, of the possibilities of which, preceding 1850, we were only dimly conscious, and so much of which had only just been added by the results of the Mexican War. It is so difficult, from the present standpoint, to realize the mighty work which has been done on the American continent in this short space of forty years, that its true bearings on this subject are sometimes disregarded. The fact that the Baltimore & Ohio Railroad, at this date, was not running its trains beyond Cumberland, Md., will give an impression of the vastness of the work which was done later.