Stabilizing a LEG, once it is broken, by using 2 boards extending from the upper thigh to the bottom of the foot is a proper way to help an injured victim in the field.
Other deposits may be from fossilized bone or bird droppings called guano. Weathering and erosion of rocks gradually releases phosphorus as phosphate ions which are soluble in water. Much of the phosphate eventually is washed into the water from erosion and leaching.
