Stir the flour and salt together in a bowl, and sift in the baking soda. Make a well in the center of the flour mixture, and pour in the buttermilk. Stir the mixture quickly together into a dough, and turn out onto a floured work surface. Knead the dough a few times, just until it comes together. Gently form the dough into a flattened, round cake about 1/2 inch thick, and cut the round into quarters with a floured knife.