The Mersey is to Liverpool what the Thames is to London--the grand channel of mercantile prosperity--the main artery that carries health and vigour into the heart of the city, and thence distributes them by a thousand ramifications through all classes of the community. The navigation of this river has long been an object of primary import to the prosperity of our national trade; and therefore every suggestion which promised to obviate and remove those impediments which nature had thrown in the way, has been met with the greatest promptness and liberality. Whatever it was possible for art to accomplish has been attempted, and that so successfully that, if the ultimate object has not yet been obtained, the navigation of the Mersey has at least been rendered comparatively safe and expeditious. The grand enterprise for facilitating the intercourse between Liverpool and Manchester was commenced in 1720, when a canal was formed, and the navigation of the Mersey and Irwell was so greatly improved, that the "flats"--which were previously ten or eleven days in going from one town to the other--could now, by taking advantage of the tide, accomplish the same distance in as many hours. How amazingly this distance has been again shortened in our own times, by the introduction of steam power, is familiar to every one. The rise and expansion of Liverpool--in all that regards it as a mercantile emporium--have taken place within the last two centuries. In 1650, the town--a mere fishing hamlet--consisted of only five or six streets. A pool, branching from the river, extended over the space now occupied by the new Custom-house and the three streets adjoining; and, for the convenience of intercourse, a ferry-boat was kept at the corner of Church-street and Whitechapel. This ferry was at last superseded by a bridge, erected by the proprietor of the land, Lord Molyneux; and since that period the advancement of the Mersey in the list of great navigable rivers has been unprecedentedly rapid and successful. The grand municipal improvements, however, have all been effected within the last century. During that interval, splendid squares, streets, and public monuments have sprung up into existence. Previously to that epoch there was no spirit, no scope for commercial enterprise, and consequently no harbour, nor dock, nor warehouse. But now spacious harbours extend for several miles along the bank of the Mersey: on the bosom of the river stately merchantmen, outward or homeward bound, laden with the produce of every clime, are continually passing and repassing; while the usual embellishments which follow a train of successful industry are apparent at every step of our progress, adding ever varying features of beauty and animation to the landscape. He who would form a just estimate of the vast and unlimited resources of this great commercial city, should spend at least a day, partly in a promenade along the banks, and partly on the spring-tide of the Mersey.