Black locust. It loses its thorns when the tree matures, but you'll find the thorns still on younger branches.
Definitely NOT hickory.
In general, you must not be using dead wood from dead trees that have been laying down in the woods for God knows how long. The only three exceptions in my mind would be yew, osage and black locust. All other woods will deteriorate (fungi, bacteria, water decay) in a matter of weeks. This piece of black locust still looks fine and should make a good bow.