1. A blockage of inwashed mud, sand or boulders in a cave passage. Most boulder chockes are formed by collapse of a passage roof and may have an open chamber or shaft above them; others are formed by collapse and inwashed debris where a large old passage is cut by a hillside. A passable route through a choke may be opened by excavation, and thereby lead to discovery of new passage - as was done so successfully in Ogof Agen Allwedd [9]. 2. Rock debris or cave fill completely blocking a passage [10].