▁mass if , ▁a ▁very ▁old ▁range ▁that ▁also ▁extends ▁in ▁Norm andy ▁and ▁the ▁Pays ▁de ▁la ▁Lo ire ▁region . ▁Because ▁of ▁this ▁continu ity , ▁the ▁Bre ton ▁border ▁with ▁the ▁rest ▁of ▁France ▁is ▁not ▁marked ▁by ▁any ▁strong ▁ge ographical ▁land mark , ▁apart ▁from ▁the ▁river ▁Cou es non , ▁which ▁separ ates ▁Brit t any ▁from ▁Norm andy . ▁ ▁The ▁Arm or ican ▁mass if ▁reaches ▁its ▁maximal ▁elev ation ▁outside ▁of ▁Brit t any , ▁in ▁neighbour ing ▁May enne , ▁at ▁ 4 1 7 ▁m , ▁and ▁s lop es ▁towards ▁the ▁west ▁before ▁straight ening ▁on ▁its ▁western ▁extrem ity , ▁with ▁the ▁Mont agn es ▁No ires ▁and ▁the ▁Mont s ▁d ' Arr ée . ▁The ▁highest ▁hill ▁in ▁Brit t any ▁is ▁the ▁Roc ' h ▁R uz ▁in ▁the ▁Mont s ▁d ' Arr ée , ▁at ▁. ▁It ▁is ▁closely ▁followed ▁by ▁several ▁neighbour ing ▁hills ▁cul min ating ▁at ▁around ▁ 3 8 4 ▁m ▁above ▁sea ▁level . ▁ ▁Coast al ▁areas ▁are ▁usually ▁named ▁Arm or ▁or ▁Ar vor ▁(" by ▁the ▁sea " ▁in ▁Bre ton ), ▁and ▁the ▁in land ▁is ▁called ▁Ar go at ▁(" by ▁the ▁forest "). ▁The ▁best ▁so ils ▁were ▁primit ively ▁covered ▁by ▁large ▁for ests ▁which ▁had ▁been ▁progress ively ▁replaced ▁by ▁b oc age ▁during ▁the ▁Middle ▁A ges . ▁The ▁Bre ton ▁b oc age , ▁with ▁its ▁small ▁fields ▁en closed