, ▁ign imb rit es , ▁co arse ▁sand st ones ▁and ▁others . ▁T ors ▁are ▁mostly ▁less ▁than ▁ ▁high . ▁Many ▁hypoth eses ▁have ▁been ▁proposed ▁to ▁explain ▁their ▁origin ▁and ▁this ▁remains ▁a ▁topic ▁of ▁discussion ▁among ▁ge olog ists ▁and ▁ge omorph olog ists , ▁and ▁physical ▁ge ograph ers . ▁It ▁is ▁considered ▁likely ▁that ▁t ors ▁were ▁created ▁by ▁ge omorphic ▁processes ▁that ▁differ ed ▁widely ▁in ▁type ▁and ▁duration ▁according ▁to ▁regional ▁and ▁local ▁differences ▁in ▁climate ▁and ▁rock ▁types . ▁ ▁For ▁example , ▁the ▁D art mo or ▁gran ite ▁was ▁emp la ced ▁around ▁ 2 8 0 ▁million ▁years ▁ago , ▁with ▁the ▁cover ▁rocks ▁er oded ▁away ▁soon ▁afterwards , ▁expos ing ▁it ▁to ▁chemical ▁and ▁physical ▁weather ing ▁processes . ▁Where ▁joint s ▁are ▁closely ▁spac ed , ▁the ▁large ▁cry st als ▁in ▁the ▁gran ite ▁readily ▁dis integr ate ▁to ▁form ▁a ▁sand y ▁reg ol ith ▁known ▁locally ▁as ▁grow an . ▁This ▁is ▁readily ▁stri pped ▁off ▁by ▁sol if lu ction ▁or ▁surface ▁was h ▁when ▁not ▁protected ▁by ▁veget ation , ▁not ably ▁during ▁prolong ed ▁cold ▁phases ▁during ▁the ▁Qu atern ary ▁ice ▁ages ▁- ▁per ig la ci ation . ▁ ▁Where ▁joint s ▁happen ▁to ▁be ▁unus ually ▁widely ▁spac ed , ▁core ▁blocks ▁can ▁surv ive ▁and ▁escape ▁above ▁the ▁weather ing ▁surface , ▁developing ▁into ▁t ors . ▁These ▁can ▁be ▁mon ol ith ic , ▁as ▁at