▁Hay tor ▁and ▁Black ing stone ▁Rock , ▁but ▁are ▁more ▁usually ▁sub div ided ▁into ▁stack s , ▁often ▁arranged ▁in ▁a ven ues . ▁Each ▁stack ▁can ▁compr ise ▁several ▁t iers ▁or ▁pill ows , ▁which ▁may ▁become ▁separated : ▁rock ing ▁pill ows ▁are ▁called ▁log an ▁stones . ▁These ▁stack s ▁are ▁vulner able ▁to ▁fro st ▁action ▁and ▁often ▁collapse ▁leaving ▁tra ils ▁of ▁blocks ▁down ▁the ▁s lop es ▁called ▁cl itter ▁or ▁cl atter . ▁We ather ing ▁has ▁also ▁given ▁rise ▁to ▁circular ▁" rock ▁bas ins " ▁formed ▁by ▁the ▁accum ulation ▁of ▁water ▁and ▁repeated ▁free zing ▁and ▁th aw ing . ▁An ▁example ▁is ▁found ▁at ▁K es ▁Tor ▁on ▁D art mo or . ▁ ▁D ating ▁of ▁ 2 8 ▁t ors ▁on ▁D art mo or ▁showed ▁that ▁most ▁are ▁surprising ly ▁young , ▁less ▁than ▁ 1 0 0 , 0 0 0 ▁years ▁old , ▁with ▁none ▁over ▁ 2 0 0 , 0 0 0 ▁years ▁old . ▁They ▁probably ▁emer ged ▁at ▁the ▁start ▁of ▁the ▁last ▁major ▁ice ▁age ▁( De vens ian ). ▁By ▁contrast , ▁in ▁the ▁Scottish ▁C air ng orm s ▁which ▁is ▁the ▁other ▁classic ▁gran ite ▁tor ▁concentration ▁in ▁Britain , ▁the ▁oldest ▁t ors ▁dated ▁are ▁between ▁ 2 0 0 ▁and ▁ 6 7 5 , 0 0 0 ▁years ▁old , ▁with ▁even ▁gla cially - mod ified ▁ones ▁having ▁dates ▁of ▁ 1