Preheat oven to 350°F. Grease two 8 x 4-inch loaf pans. Sift together dry ingredients and set aside. In a large mixing bowl, cream butter; gradually add sugar and continue beating. Add eggs one at a time, beating well after each addition. Add dry ingredients alternately with buttermilk. Stir in raisins. Transfer batter to prepared loaf pans and bake for 1 hour or until knife inserted in center comes out clean and dry.