Oppression in Southwestern Missouri.

We were shown a few days since, a letter from Dr. Z.L. Slavens of Buffalo, Mo., some thirty miles north of Springfield. The letter is dated St. Charles Co.-- near St. Louis. He says:

"You may realize in some degree the terrible crisis upon us as a people, and a nation, but I assure you, you cannot feel all the stunning force of the consequence of the rebels gaining a foothold in a loyal country. Until the great battle at Springfield, we, the union men, held Southwestern Missouri free from the scourge of secessionism. But when Lyon's brave command was compelled to fall back upon Rolla, they, (the secessionists) overran the country, and we have had to flee for our lives, leaving what of property we could not hastily snatch up, and convey with us. We are all ruined so far as worldly possessions are concerned. When we started we knew not what to do. We have brought our families, (mine and father's) across the Missouri river, where we are trying to make some temporary provision for them. What will become of us God only knows-- driven from our homes and rendered penniless. It may be, when we drive the rebels out, we can return and at least claim our lands-- whether anything else, I know not. The secessionists are devastating the whole country. I shall shortly write you more at length of affairs in South-western Missouri. I am much grieved at my misfortunes." Z. L. Slavens.

Greencastle (Indiana) Banner, September 12, 1861.