Sift flour, salt, soda into bowl. Stir in whole wheat flour, blending. Rub in margarine lifting fingers high when mixing. Add buttermilk all at once, using fork. Add more, if needed, to make soft dough. Knead until smooth. Place on greased baking sheet; mark to deeply into four sections. Bake at 190ºC or 40 minutes. Allow to go cold on rack before cutting. Serve with butter. Preparation time: 20 minutes Baking time: 40 minutes