In the article on the great plain, in the May number of this Review, we gave prominence to the two great external gateways of commerce offered to its people in their intercourse with the rest of the world: that is to say, the Mississippi river entrance into the Gulf of Mexico, and the outlet of the lakes through St. Lawrence and Hudson rivers. These constitute the present great routes of commerce of the people of the plain, and draw to the cities on the borders of the great lakes and rivers the trade of the surrounding country. Between the cities of the great rivers and lakes there has of late sprung up a friendly rivalry, each having some peculiar advantages, and all, in some degree, drawing business into their laps for the benefit of their rivals. That is to say: river cities gather in productions from the surrounding districts which seek an eastern market through lake harbors; and lake cities perform the same office for the chief river cities. Each year increases, to a marked extent, the intercourse which these two classes of cities hold with each other; and it may be safely anticipated that no long period will elapse before this intercourse will become more important to them than all their commerce with the world beside. In comparing the interior cities of the great plain, situated on the navigable rivers, with those located on the borders of the lakes, two considerations bearing on their relative growth should be kept in view. The river cities were of earlier growth, the settlement from the Atlantic States having taken the Ohio river as the high-road to their new homes, many years before the upper lakes were resorted to as a channel of active emigration. This gave an earlier development to country bordering the central rivers, the Ohio, Wabash, Illinois, and Lower Missouri. The States of Kentucky and Tennessee, also, had been pretty well settled, in their more inviting portions, before any considerable inroad had been made on the wilderness bordering on the upper lakes. Owing to these and other circumstances, the river cities, Pittsburg, Cincinnati, Louisville, and others of less note, were well advanced in growth, before the towns on the lakes had begun, in any considerable degree, to be developed. Another advantage the river cities possessed in their early stage, and which they still hold; that of manufacturing for the planting States bordering the great rivers. For many years, in a great variety of articles of necessity, they possessed almost a monopoly of this business. Of late, transportation has become so cheap, that the planters avail themselves of a greater range of choice for the purchase of manufactured articles, and the lake cities have commenced a direct trade with the plantation States, which will doubtless increase with the usual rapidity of industrial development in the fertile West.