We clip the following from the New York Post of Saturday:

“New Orleans would seem to be the natural mart for receiving and exporting the surplus grain of the country drained by the Mississippi river and its affluents. But, in truth, it receives but little beyond its own wants for consumption, and exports very little by sea.
“The lake cities received, during the year 1860, not less than 80,000,000 bushels, estimating the barrel of flour at five bushels. Much the largest portion of this was grown within the basin of the Mississippi.
“New Orleans, during the fiscal year ending 31st August, received of grain, in all forms, less than 13,000,000 bushels, valued at $10,436,510.
“The receipts at the principal lake ports for the year 1860 were:
Chicago 36,500,000 bus.
Toledo 14,504,903 bus.
Milwaukie 11,040,488 bus.
Detroit 6,780,099 bus.
Cleveland, Sandusky and other lake ports, estimated low at 11,174,510 bus.
Total 80,000,000 bu.”

These figures confirm the statement which we made in an article published some weeks since, that the freedom of the “Mouth of the Mississippi,” was no longer the great necessity of the foreign commerce of the grain growing regions of the North West. The overshadowing importance of the mouth of the Mississippi to Western foreign commerce is a tradition, not a reality. We are, so far as our trade with Europe is concerned, quite as much interested in the freedom of the Erie Canal as in that of the mouth of the Mississippi. It is found cheaper to send our produce for foreign markets over the Great Eastern Railroads—through the Erie Canal, or by way of the Lakes, than to send it down the Mississippi and around by the Capes of Florida and along the dangerous Southern coast. The Federal Government paid fifteen millions of dollars for Louisiana, that is to say for the mouth of the Mississippi, as an outlet for the Commerce of the West. But by individual and State enterprise ten times the sum has been paid in constructing a vast system of Railroads, and a great Canal, by which the Western people command a shorter route to the Ocean.

The greater part of the commerce on the Mississippi River must continue to be as it has been, that between the people of the several States. No change in political relations is likely to affect this commerce largely and permanently. There will be, in any supposable event, freedom of trade between the States.—The people north and South will see to it that there is no protracted interruption, either by the acts of war or the provisions of treaties, in their intercourse. Our steamboats go down the river loaded with articles from our fields and shops, for which our merchants have Southern cash in their pockets. Now we are hardly at liberty to suppose that those steamers will be subjected to any great damage from fanatics on the banks of the river. The extreme Southerners may do a great many rash and mad things, and they have set precedents for acts of folly otherwise unimaginable, but it is not probable that Southern fire-eaters will sink or confiscate boats employed in the transmission of their property. The flash-in-the-pan of the gun aimed at the A. O. Tylor, illustrates the policy of the Governor of Mississippi. It was a flash-in-the-pan, and he made haste to invent excuses for his conduct and to remove his battery.

If the whole of the Southern States should in process of time find themselves independent politically, it is a clear proposition that no step would be taken toward commercial independence. They would want our meat, breadstuffs, whisky, machinery and furniture, just as badly as ever they did, and would have them too in proportion to their capacity to settle the bills. We have long been threatened with the loss of the Southern trade, and yet, at the moment of the wildest excitement in the South, the orders pour into the Northern cities, accompanied by the cash, for the essentials of life, and the ten thousand things of minor importance which the South does not produce and must have. The laws of trade do not respect political prejudices. The present demonstration of this fact, which is manifest to all—which is so plainly written in the history of the time, that even the fool reads as he runs—even the Enquirer cannot mistake it—relieves us of that celebrated scare-crow—the loss of Southern trade, if we do not vote to please Southern politicians. When a journal or stump speaker tells us that we are about to lose the Southern trade, it is a charge against the South of barbarism that the facts do not sustain. Whatever there is of real union between the North and the South, will survive all the eventualities of the present crisis. Even if the political bonds of union should be severed, there will be commercial and social intercourse, in which there would be the soul of Union. We must, however, in case of the disruption of the Union, endure heavy losses. The theory that the dissolution of the Union would be a good thing for us, is untenable and injurious. We should suffer loss—first, from that shock to public confidence which we are already experiencing; next, from the falling off of Southern commerce, consequent upon the depreciation of that section. If the South submits to the revolutionists, it is quite certain that she must support standing armies and have many costly experiences, which will vastly increase the rate of taxation. There will be a still greater fall in the value of real estate and slaves. Society will be demoralized, and impoverishment ensue. The South will thus become less able to purchase the necessaries of life and labor, which we have had the profit of furnishing. Our difficulty is that we see our best customer pursuing a course that must render the custom less profitable. There is no danger or hope that the South will be successful in looking elsewhere for friends. The people of the North are the best friends the South has in the world; and if the South attempts to desert us for strangers, the fact will soon become obvious to all observant mankind.

The idea of a direct trade of the South with Europe, which is entertained in some Southern quarters, that profess to be well-informed, and feared in some northern quarters where common sense is scarce, is a downright humbug. The South will continue to receive from the North those articles, the sum of which is annually equal to the value of the whole cotton crop, and which her political economists are so kind as not to take into consideration in discussing the relative prosperity of the North and South. Neither France nor England, nor any other European country, could furnish the articles that make up our Southern export trade; and whether the high protective tariff or free trade prevails, we shall continue to have the monopoly of that trade. But we are told that the South will supply herself with the articles now purchased in the North—that she is about to “plant corn,” and do many other things equally independent and destructive. There is nothing at which a Southern field hand can be employed so profitably as in the raising and picking of cotton. A good cotton hand is worth from three to four hundred dollars a year. Now the planter who would employ his cotton hands in raising corn would find it very dear corn. He can make more money by raising all the cotton he can, and buying corn with his cotton money. This is the crucial test. The small politicians who edit newspapers in the little towns of the cotton States, may say “plant corn,” as much as they please. The planters know what to plant, and where their markets are. They will continue to plant cotton and buy corn. As for manufactories in the South, they will not flourish so as to materially alter the relations of the sections, before the present policy of the masters toward the slaves undergoes the radical change of looking toward ultimate emancipation. The South can work its own impoverishment; but it can only stab our prosperity through its own. It cannot change the currents of commerce, nor repeal the laws of soil, climate and labor.

The community most interested in the perfect freedom of the mouth of the Mississippi, is that of New Orleans. Every restriction placed upon commerce there—every movement that weakens confidence—is a blow at the prosperity of the city of New Orleans. Commerce will take to itself wings, and sail away from her. Every development of a mob spirit—every act of bad faith—every proceeding that will startle the bare nerves of capital—is an assassin assault upon the very elements of her vitality. They need not flatter themselves that the North is to be the sufferer for their sins. The North may be chief mourner. It is not her funeral.