In a large bowl, combine the flour and salt. Pour in the sourdough starter and oil and mix well. Combine water and baking soda in a cup, stir and then mix into dough. Drop biscuit-size balls of dough onto an ungreased baking sheet. If using a reflector oven, bake next to a hot fire until biscuits begin to brown, about 16 minutes, rotating the baking sheet once halfway through cooking. In a conventional oven, bake biscuits until they begin to brown, 10 to 15 minutes.