▁( fill ing , ▁heart ing ). ▁ ▁The ▁final ▁layer ▁on ▁the ▁top ▁of ▁the ▁wall ▁also ▁consists ▁of ▁large ▁stones , ▁called ▁cap st ones , ▁cop ing ▁stones ▁or ▁cop es . ▁As ▁with ▁the ▁tie ▁stones , ▁the ▁cap st ones ▁span ▁the ▁entire ▁width ▁of ▁the ▁wall ▁and ▁prevent ▁it ▁breaking ▁apart . ▁In ▁some ▁areas , ▁such ▁as ▁South ▁Wales , ▁there ▁is ▁a ▁tradition ▁of ▁placing ▁the ▁cop ing ▁stones ▁on ▁a ▁final ▁layer ▁of ▁flat ▁stones ▁slightly ▁wider ▁than ▁the ▁top ▁of ▁the ▁wall ▁proper ▁( cover b ands ). ▁ ▁In ▁addition ▁to ▁gates ▁a ▁wall ▁may ▁contain ▁smaller ▁pur pos ely ▁built ▁g aps ▁for ▁the ▁passage ▁or ▁control ▁of ▁wild life ▁and ▁liv est ock ▁such ▁as ▁sheep . ▁The ▁smaller ▁holes ▁usually ▁no ▁more ▁than ▁ 8 ▁inches ▁in ▁height ▁are ▁called ▁' B olt ▁Hol es ' ▁or ▁' S mo ots '. ▁Lar ger ▁ones ▁may ▁be ▁between ▁eigh teen ▁and ▁ 2 4 ▁inches ▁in ▁height , ▁these ▁are ▁called ▁a ▁' C ri pp le ▁H ole '. ▁ ▁B ould er ▁walls ▁are ▁a ▁type ▁of ▁single ▁wall ▁in ▁which ▁the ▁wall ▁consists ▁primarily ▁of ▁large ▁b ould ers , ▁around ▁which ▁smaller ▁stones ▁are ▁placed . ▁Single ▁walls ▁work ▁best ▁with ▁large , ▁fl atter ▁stones . ▁Ide ally , ▁the ▁largest ▁stones ▁are ▁being ▁placed ▁at ▁the ▁bottom ▁and ▁the ▁whole ▁wall ▁tap ers ▁toward ▁the ▁top . ▁Sometimes ▁a ▁row ▁of ▁cap st