▁lim estone , ▁so ils ▁in ▁Brit t any ▁are ▁usually ▁acid . ▁▁ ▁The ▁Arm or ican ▁mass if ▁straight ened ▁and ▁fl atten ed ▁several ▁times ▁during ▁the ▁formation ▁of ▁the ▁Py ren ees ▁and ▁the ▁Al ps . ▁Ch anges ▁in ▁sea ▁levels ▁and ▁climate ▁led ▁to ▁a ▁strong ▁er os ion ▁and ▁to ▁the ▁formation ▁of ▁more ▁sed iment ary ▁rocks . ▁Met am orphism ▁is ▁responsible ▁for ▁the ▁distinct ive ▁local ▁blue ▁sch ist ▁and ▁for ▁the ▁rich ▁sub so il ▁of ▁the ▁Gro ix ▁island , ▁which ▁compr ises ▁gla uc oph ane ▁and ▁e pid ote . ▁ ▁During ▁the ▁Qu atern ary ▁gla ci ations , ▁Brit t any ▁was ▁covered ▁by ▁lo ess ▁and ▁rivers ▁started ▁to ▁fill ▁the ▁valle ys ▁with ▁all uv ial ▁depos its . ▁The ▁valle ys ▁themselves ▁were ▁a ▁result ▁of ▁a ▁strong ▁t ect onic ▁activity ▁between ▁the ▁African ▁and ▁the ▁E uras ian ▁plate . ▁The ▁present ▁Bre ton ▁landscape ▁did ▁not ▁acquired ▁its ▁final ▁shape ▁before ▁one ▁million ▁years ▁ago . ▁The ▁Bre ton ▁sub so il ▁is ▁character ised ▁by ▁a ▁huge ▁amount ▁of ▁f ract ures ▁that ▁form ▁a ▁large ▁aqu ifer ▁containing ▁several ▁millions ▁square ▁meters ▁of ▁water . ▁ ▁Cl imate ▁Brit t any ▁lies ▁within ▁the ▁north ▁temper ate ▁zone . ▁It ▁has ▁a ▁change able , ▁mar itime ▁climate , ▁similar ▁to ▁Corn wall . ▁Rain fall ▁occurs ▁regularly ▁but ▁sun ny , ▁cloud less ▁days ▁are ▁also ▁common .