▁are ▁distinct ive ▁by ▁virtue ▁of ▁their ▁magnetic ▁qual ities . ▁The ▁Water ▁Tower ▁Sl ates , ▁forming ▁part ▁of ▁the ▁Hospital ▁Hill ▁Series ▁in ▁the ▁Wit w aters rand ▁Bas in , ▁include ▁a ▁fine - gra ined ▁fer ru gin ous ▁quart z ite ▁which ▁is ▁particularly ▁magnetic . ▁From ▁the ▁same ▁series ▁a ▁r ipp le ▁marked ▁quart z ite ▁and ▁a ▁spe ck led ▁bed ▁are ▁used ▁as ▁marker ▁hor iz ons . ▁ ▁On ▁a ▁much ▁smaller ▁time ▁scale , ▁marker ▁hor iz ons ▁may ▁be ▁created ▁by ▁sed iment olog ists ▁and ▁lim n olog ists ▁in ▁order ▁to ▁measure ▁de position ▁and ▁er os ion ▁rates ▁in ▁a ▁mar sh ▁or ▁p ond ▁environment . ▁The ▁materials ▁used ▁for ▁such ▁an ▁artificial ▁horizon ▁are ▁chosen ▁for ▁their ▁visibility ▁and ▁stability ▁and ▁may ▁be ▁brick ▁dust , ▁gro g , ▁sand , ▁ka olin , ▁gl itter ▁or ▁f eld s par ▁cl ay . ▁ ▁References ▁ ▁External ▁links ▁International ▁Str at ig raph ic ▁Guide ▁- ▁Ge ological ▁Society ▁of ▁America ▁( 1 9 9 4 ) ▁- ▁Am os ▁Salvador ▁( editor ) ▁ ▁Category : Str at ig raph y ▁Category : Ge och ron ology <0x0A> </s> ▁The ▁following ▁is ▁a ▁List ▁of ▁broad c aster s ▁for ▁the ▁Detroit ▁L ions , ▁both ▁past ▁and ▁present . ▁ ▁Radio ▁ ▁Current ▁ ▁The ▁L ions ' ▁flags hip ▁radio ▁station ▁is ▁W J R ▁ 7 6 0 ▁AM . ▁Dan