, ▁revers es ▁direction ▁at ▁irregular ▁intervals . ▁ ▁The ▁we aker ▁variations ▁are ▁the ▁Earth ' s ▁magnetic ▁map . ▁ ▁Within ▁these ▁we aker ▁areas ▁the ▁local ▁directions ▁and ▁intens ities ▁change ▁gradually ▁( sec ular ▁variation ). ▁▁ ▁A ▁comp ass ▁does ▁not ▁point ▁to ▁the ▁true ▁North ▁P ole ▁but ▁to ▁a ▁direction ▁that ▁is ▁a ▁function ▁of ▁the ▁North ▁Mag net ic ▁P ole ▁and ▁the ▁local ▁sec ular ▁variation ▁to ▁yield ▁a ▁magnetic ▁decl ination . ▁The ▁magnetic ▁decl ination ▁at ▁any ▁given ▁time ▁can ▁be ▁fro zen ▁into ▁a ▁cl ay ▁formation ▁that ▁contains ▁magnet ite ▁and ▁is ▁he ated ▁above ▁the ▁Cur ie ▁point . ▁ ▁In ▁general , ▁many ▁cult ures ▁used ▁long - term ▁fire ▁hear th s ▁made ▁of ▁cl ay ▁br icks , ▁or ▁a ▁space ▁l ined ▁with ▁cl ay , ▁that ▁were ▁b aked ▁into ▁place ▁by ▁use . ▁ ▁These ▁artifact s ▁of ▁occupation ▁can ▁yield ▁the ▁magnetic ▁decl ination ▁from ▁the ▁last ▁time ▁they ▁were ▁fired ▁or ▁used . ▁Arch ae om agnet ic ▁d ating ▁was ▁described ▁in ▁the ▁ 1 9 9 2 ▁publication ▁“ P ale om agnet ism : ▁Mag net ic ▁Dom ains ▁to ▁Ge olog ic ▁Ter ran es .” ▁By ▁Robert ▁F . ▁Butler . ▁ ▁Method ology ▁Arch ae om agnet ic ▁d ating ▁requires ▁an ▁und ist urbed ▁feature ▁that ▁has ▁a ▁high ▁lik elihood ▁of ▁containing ▁a ▁rem nant ▁magnetic ▁moment ▁from ▁the ▁last ▁time ▁it ▁had