By boundary is understood, in general, every separation, natural or artificial, which marks the confines or line of division of two contiguous estates. Trees or hedges may be planted, ditches may be dug, walls or inclosures may be erected, to serve as boundaries. But we most usually understand by boundaries stones or pieces of wood Inserted in the earth on the confines of the two estates. Civ. Code La. art. 826. Boundaries are either natural or artificial. Of the former kind are water-courses, growing trees, beds of rock, and the like. Artificial boundaries are landmarks or signs erected by the hand of man, as a pole, stake, pile of stones, etc.