A SALT LAKE correspondent says, the Mormons are buying up all the United States muskets and rifles, &c., of the troops now being mustered out there. He thinks they would not hesitate a mo-ment to enter into open hostility against the Government at the bidding of Brigham Young. If Congress shall take any action unfavorable to polgamy, much trouble and bloodshed is antici-pated. Assassinations occur almost daily, and scores of leading "gentiles" have been warned. The absence of U.S. troops makes the "saints" savage for blood.