As one of the river steamers was passing Musquash Island last week, a dead body was discovered floating in the water, which being secured was identified as that of Alexander ANDERSON, blacksmith of Oromocto (Sunbury Co.) who had been missing since March last. He was last seen at the hotel of Mrs. GLASS of Gagetown (Queens Co.) and left there at a late hour intending to cross the river in the direction of Grand Lake and it is now supposed that he fell into one of the air holes so common on the St. John in the winter time.