▁section ▁of ▁the ▁line ▁from ▁Gu is borough ▁to ▁Bro tt on , ▁but ▁the ▁eastern most ▁part ▁of ▁the ▁line ▁is ▁still ▁in ▁use ▁today ▁as ▁a ▁min eral ▁railway . ▁ ▁History ▁ ▁Orig ins ▁of ▁the ▁line ▁ ▁The ▁construction ▁of ▁the ▁line ▁was ▁prompt ed ▁by ▁the ▁need ▁of ▁mine ▁own ers ▁around ▁Gu is borough ▁and ▁East ▁Cleveland ▁to ▁transport ▁their ▁iron ▁ore ▁to ▁the ▁River ▁Te es . ▁Gu is borough ▁was ▁already ▁served ▁by ▁the ▁M idd les br ough ▁and ▁Gu is borough ▁Railway ▁( M & GR ), ▁a ▁subs idi ary ▁of ▁the ▁Stock ton ▁and ▁Dar ling ton ▁( S & D ), ▁which ▁had ▁built ▁a ▁line ▁( open ed ▁in ▁ 1 8 5 4 ) ▁running ▁along ▁the ▁south ▁of ▁the ▁valley ▁in ▁which ▁Gu is borough ▁s its . ▁However , ▁the ▁line ▁was ▁an ▁incon ven ient ly ▁long ▁distance ▁from ▁the ▁luc r ative ▁iron ▁ore ▁mines ▁in ▁the ▁north ▁of ▁the ▁valley , ▁along ▁the ▁south ▁fl ank ▁of ▁the ▁Est on ▁Hills , ▁and ▁provided ▁no ▁connection ▁at ▁all ▁for ▁mines ▁east ▁of ▁Gu is borough . ▁The ▁M & GR ▁had ▁been ▁built ▁by ▁a ▁group ▁of ▁industrial ists ▁based ▁in ▁Stock ton ▁and ▁Dar ling ton ▁who ▁used ▁it ▁to ▁service ▁their ▁own ▁mines , ▁deliber ately ▁avoid ing ▁the ▁est ates ▁of ▁their ▁riv als . ▁It ▁only ▁provided ▁a ▁minimal ▁passenger ▁service ▁to ▁M idd les br ough ▁– ▁one