Preheat oven to 350 degrees F (175 degrees C). Grease one 9 x 13 inch pan.
Dissolve soda in boiling water. Set aside.
Mix together flour, brown sugar, salt, and vegetable oil to form a crumb-like mixture. Reserve 1 cup of the crumbs. Mix the remaining crumbs with the water and soda mixture. Pour batter into the prepared pan. Sprinkle the reserved crumbs on top.
