ed ▁here ▁for ▁river ▁protection ▁since ▁the ▁ 1 9 2 0 s . ▁In ▁the ▁time ▁since ▁numerous ▁items ▁have ▁been ▁recovered ▁for ▁pres ervation ▁purposes . ▁ ▁History ▁During ▁the ▁history ▁of ▁New ▁Zealand ▁Rail ways , ▁all ▁locomot ives ▁and ▁rolling ▁stock ▁have ▁reached ▁or ▁will ▁reach ▁a ▁state ▁of ▁ob sol esc ence . ▁When ▁the ▁cost ▁of ▁sc rap ▁metal ▁dro ps ▁below ▁an ▁economic ▁level , ▁other ▁uses ▁for ▁locomot ives ▁and ▁rolling ▁stock ▁are ▁found . ▁Some ▁were ▁dump ed ▁in ▁locomot ive ▁d umps ▁to ▁aid ▁protection ▁of ▁the ▁railway ▁against ▁er os ion ▁or ▁soft ▁ground . ▁ ▁The ▁ge ology ▁of ▁the ▁South land ▁Pla ins ▁is ▁built ▁upon ▁the ▁loose ▁rock ▁which ▁has ▁was hed ▁down ▁from ▁the ▁Southern ▁Al ps ▁over ▁many ▁centuries . ▁The ▁loose ▁rock ▁and ▁surrounding ▁mud ▁at ▁the ▁O re ti ▁River ▁crossing ▁at ▁Bran x hol me ▁provided ▁an ▁un stable ▁formation ▁for ▁the ▁railway ▁lines ▁running ▁west ▁of ▁In ver c arg ill ▁to ▁Oh ai , ▁River ton ▁and ▁Tu at ap ere . ▁ ▁Initial ly ▁large ▁amounts ▁of ▁rock ▁and ▁other ▁de br is ▁were ▁t ipped ▁at ▁Bran x hol me ▁to ▁stabil ise ▁the ▁line , ▁however , ▁this ▁did ▁not ▁stay ▁in ▁place , ▁particularly ▁after ▁heavy ▁ra ins ▁and ▁subsequent ▁flo oding . ▁In ▁ 1 9 2 7 , ▁when ▁sc rap ▁steel ▁was ▁an ▁une conom ic ▁proposition , ▁New ▁Zealand ▁Rail ways ▁started ▁dump ing