( ( As ( ( the rocks ) ( ( ( cool ( from lava ) ) , ) ( for ( ( instance ( at ( the ( deep ( mid-ocean ridges ) ) ) ) ) ( where ( ( ( the ( earth 's ) ) ( surface plates ) ) ( are formed ) ) ) ) ) ) ) ) ( , ( crystals ( ( ( line up ) ( with ( ( the direction ) ( of ( the ( magnetic field ) ) ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (IN As) (S (NP (DT the) (NNS rocks)) (VP (VBP cool) (PP (IN from) (NP (NN lava))) (, ,) (PP (IN for) (NP (NP (NN instance)) (PP (IN at) (NP (DT the) (JJ deep) (JJ mid-ocean) (NNS ridges))) (SBAR (WHADVP (WRB where)) (S (NP (NP (DT the) (NN earth) (POS 's)) (NN surface) (NNS plates)) (VP (VBP are) (VP (VBN formed)))))))))) (, ,) (NP (NNS crystals)) (VP (VBP line) (PRT (RP up)) (PP (IN with) (NP (NP (DT the) (NN direction)) (PP (IN of) (NP (DT the) (JJ magnetic) (NN field)))))) (. .)))
As the rocks cool from lava, for instance at the deep mid-ocean ridges where the earth's surface plates are formed, crystals line up with the direction of the magnetic field.
(ROOT (S (NP (JJ Mineral) (NNS crystals)) (VP (VBP are) (VP (VBN formed) (SBAR (WHADVP (WRB when)) (S (NP (JJ hot) (NN lava)) (VP (VBZ cools)))))) (. .)))