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Type	Originator	Title	Date
	Haigh,D & Cordingley, J	Adventures Underground	2017
	Waltham,A	Caves	1974
	Geyer,E (ed)	Expedition Gunung Lanno Malaysia	2001
	Brunet,P	La Grotte de Saint Marcel d'Ardeche [with DVD and loose survey]	2008
	Trebuchon,J	La saga de l'aven d'orgnac, Issirac	2000
	Trench,R & Hillman,E	London Underground	1994
	Irwin,D.J & Jarrett,A	Mendip Underground	1993
	Cambrian Archaeological Association [Archaeologia Cambrensis 117, pp.18-71]	Ogof yr Esgyrn	1968
	Casteret,N	Ten years under the earth	1939
	Walker,T.A	The Severn Tunnel	[1888]