▁hiding - p laces . ▁In ▁most ▁cases , ▁between ▁two ▁and ▁four ▁sub - ch amb ers ▁are ▁present , ▁exc av ated ▁later ally ▁from ▁the ▁floor ▁level , ▁the ▁roof ▁being ▁supported ▁by ▁pill ars ▁of ▁ch alk ▁left ▁standing . ▁ ▁Distribution ▁ ▁There ▁are ▁many ▁under ground ▁exc av ations ▁in ▁the ▁south ▁of ▁England , ▁also ▁found ▁to ▁some ▁extent ▁in ▁the ▁Mid lands ▁and ▁the ▁north , ▁but ▁true ▁den e hol es ▁are ▁found ▁chief ly ▁in ▁those ▁parts ▁of ▁Kent ▁and ▁Es sex ▁along ▁the ▁lower ▁banks ▁of ▁the ▁Th ames . ▁With ▁one ▁exception ▁there ▁are ▁no ▁recorded ▁spec im ens ▁farther ▁east ▁than ▁those ▁of ▁the ▁Gray s ▁Th ur rock ▁district , ▁situated ▁in ▁H ang man ' s ▁Wood , ▁on ▁the ▁north , ▁and ▁one ▁near ▁Chal lock ▁on ▁the ▁south ▁side ▁of ▁the ▁river ▁south ▁of ▁Fa ver sh am . ▁Is ol ated ▁spec im ens ▁have ▁been ▁discovered ▁in ▁various ▁parts ▁of ▁Kent ▁and ▁Es sex , ▁but ▁the ▁most ▁important ▁groups ▁have ▁been ▁found ▁at ▁Gray s ▁Th ur rock , ▁in ▁the ▁districts ▁of ▁W ool wich , ▁Ab bey ▁Wood ▁and ▁B ex ley , ▁and ▁at ▁Gra ves end . ▁Those ▁at ▁B ex ley ▁and ▁Gray s ▁Th ur rock ▁are ▁the ▁most ▁valuable ▁still ▁existing . ▁It ▁is ▁generally ▁found ▁that ▁the ▁tool ▁work ▁on ▁the ▁roof ▁or ▁ce iling ▁is ▁rough er ▁than ▁that ▁on ▁the ▁walls , ▁where