[The subject of the Missouri state bill, involves, in our opinion, an agricultural question, important to the last degree to the farmers of America:--Whether that great country west of the Mississippi, compared with which all the United States are small, shall, in future ages, be dotted over with pleasant villages and comfortable farm houses, and cultivated by the industrious owners of the soil, each vieing with his neighbour in beautifying the face of nature: or be blotted and defaced by innumerable wretched habitations of miserable slaves, with here and there, on distant eminences, the _lone_ mansions of their masters. Whether that great country, now left rich by nature, shall be converted into barren wastes by continued exhausting crops of tobacco and Indian corn, without one shovel-ful of manure to invigorate the expiring soil, as has been the case in some of the fine districts of Virginia and Maryland; or whether it shall be covered with luxuriant fields of wheat, rich meadows and innumerable herds.--Viewing this great national question, so intimately connected with our favourite subject, we feel the more interest by giving an insertion to the following communication of our correspondent SANDIFORD.]--_Ed._ FOR THE RURAL MAGAZINE. _Extension of Slavery._ It is the great and distinguishing feature of our free government, that it is built upon the eternal principles of justice and rectitude. The passions and the interests of its subjects or administrators may pervert its original design, and wield the power it confers to the purposes of oppression or licentiousness. So long, however, as we have access to the charter of our constitution, the great original fountain of our laws, we may renew or purify those streams which have become choked up or polluted. It forms a perpetual and unerring standard by which to judge of principles and policy; and whatever measures are found wanting in its scale, may safely be pronounced to be unwise and unsound. The flux and change of opinions and interests, the perpetual encroachments of wealth and power, the decay of old prejudices and jealousies, and the rise of new ones, wear away continually the old landmarks, and imperceptibly give to our institutions a new aspect and new bearings. While we admit this flexibility to be in a certain measure necessary for the conservation of peace and union, we must steadily insist upon its being limited by the great leading features of the constitution, and that reference should constantly be had to first principles, as to a fountain of life and strength.