Take any common map of the United States and rule an air line across it from Baltimore to St. Louis, and midway between the two it will strike Cincinnati--the great inland centre of trade--traversing at the same time those wonderfully fertile valleys which lie between the latter point and the Mississippi river. Now let it be remembered that since the introduction of railways fluvial navigation has been, to a considerable extent, superseded by inland transport, because of the greater speed and certainty of the latter. Let it be remembered also that the migration westward is incessantly going on, and that with every farm opened within striking distance of a great arterial railway, or its anastomosing branches, a certain amount of freight must find its way to the seaboard markets, while the demand for manufactured products, and for domestic or foreign commodities, in exchange for breadstuffs or raw material, must necessarily increase; thereby adding greatly to the prosperity of the commercial centre towards which articles of export tend, and from which imports in return are drawn. It would be difficult to estimate the value of what this trade will be fifty years hence, or what the population of Baltimore, situated as she is, will by that time have become. Reasoning from causes to effects, and presuming that ordinary perseverance will be used in promoting the interests of our city, industrially and commercially, we are justified in believing that its progress must be in an accelerated ratio, and that there are those now living who will look back with surprise and wonder at its growth and magnitude, as we have done while comparing its present aspect with that which it exhibited within our own memory." It is a remarkable fact, but one not at all surprising to those whose philosophy leads them to think aright, that Baltimore and St. Louis, the two most prosperous cities in the slave States, have fewer slaves in proportion to the aggregate population than any other city or cities in the South. While the entire population of the former is now estimated at 250,000, and that of the latter at 140,000--making a grand total of 390,000 in the two cities, less than 6,000 of this latter number are slaves; indeed, neither city is cursed with half the number of 6,000. In 1850, there were only 2,946 slaves in Baltimore, and 2,656 in St. Louis--total in the two cities 5,602; and in both places, thank Heaven, this heathenish class of the population was rapidly decreasing. The census of 1860 will, in all probability, show that the two cities are entirely exempt from slaves and slavery; and that of 1870 will, we prayerfully hope, show that the United States at large, at that time, will have been wholly redeemed from the unspeakable curse of human bondage.