The Spanish expedition against Mexico.
--It is reported that a Spanish expedition against Mexico was being organized at Havana. Five thousand infantry will disembark early in October at Vera Cruz, thence marching direct to the city of Mexico. Six screw-frigates, two steamers, and numerous transports are also to be employed.A decision of Marshal O'Donnell is published in the Madrid Gazette to the Captain General of Porto Rico. It declares the principle that a slave who touched the soil of Spain must be considered as emancipated even without the consent of his former master.