Dissolve soda in buttermilk; stir well, and set aside.
Combine flour, sugar, and salt; stir well. Cut in shortening with a pastry blender until mixture resembles coarse meal. Reserve 3/4 cup flour mixture for topping.
Add baking powder, cinnamon, buttermilk mixture, and eggs to remaining flour mixture; stir well.
Pour batter into a well-greased 9-inch square pan. Sprinkle reserved flour mixture over batter, and press into batter. Bake at 350° for 30 minutes or until a wooden pick inserted in center comes out clean.