Steamboat Combination.--The Buffalo papers announce that an association has been formed by the proprietors of the steamers, running on the Lakes, for the remainder of the season. The rates agreed upon are as follows: To any port on Lake Michigan, Cabin $10, Steerage $5; to Cleveland $3 and $1.50; to Detroit $4 and $2. Freight 50 cents per 100 lb. and $1 bbl. bulk.