km ▁east ▁of ▁the ▁town ▁of ▁Al va , ▁and ▁almost ▁certainly ▁exceed ed ▁ 5   km ▁vert ically . ▁The ▁deep est ▁depos its ▁of ▁coal ▁measures ▁are ▁obviously ▁found ▁in ▁this ▁region , ▁but ▁this ▁has ▁not ▁been ▁m ined ▁to ▁its ▁full ▁extent , ▁probably ▁due ▁to ▁the ▁great ▁depth ▁involved . ▁ ▁The ▁point ▁of ▁maximum ▁down wards ▁movement ▁south ▁of ▁the ▁fault ▁lies ▁just ▁south ▁of ▁the ▁Silver ▁Glen , ▁which ▁happens ▁to ▁be ▁the ▁part ▁of ▁the ▁O ch il ▁Hills ▁where ▁the ▁greatest ▁extent ▁of ▁min eral isation ▁has ▁been ▁discovered . ▁The ▁min er als , ▁including ▁or es ▁of ▁silver ▁and ▁c ob alt , ▁were ▁probably ▁emp la ced ▁by ▁hydro ther mal ▁solutions ▁per col ating ▁up wards ▁through ▁various ▁minor ▁fault s ▁and ▁f ract ures , ▁in ▁the ▁T ert i ary ▁period . ▁ ▁The ▁O ch il ▁F ault ▁remained ▁active ▁throughout ▁ge ological ▁time , ▁and ▁some ▁later ▁movements ▁allowed ▁intr us ive ▁er u ptions ▁of ▁di or ite ▁or ▁quart z - d ol er ite ▁to ▁rise ▁at ▁various ▁places ▁along ▁its ▁length . ▁▁ ▁Modern ▁movements ▁of ▁the ▁fault ▁are ▁very ▁minor ▁but ▁occasionally ▁give ▁rise ▁to ▁disc ern ible ▁earth qu akes , ▁particularly ▁in ▁the ▁village ▁of ▁Men str ie , ▁and ▁the ▁town ▁of ▁Till ic oul try . ▁However ▁the ▁latter ▁may ▁be ▁easily ▁confused ▁with ▁the ▁collapse ▁of ▁old ▁room ▁and ▁pill ar ▁coal ▁mine ▁work ings