Uppsii Mississippi Op ex.—The Mississippi is open to St. Paul, the ice-having given way last week. The steamer Greek Slave, which wintered at St. Paul, has arrived at Dubuque, and. the Nominee and War Eagle have .both started for Minnesota. Immigration to Northan Iowa and Minnesota has already commenced. It is fullv a month earlier than usual, and the4prospect of a rapid settlement of these fail lands during the coming season is very good,