 The geology of Brownhills comprises mainly red clay marl overlying Triassic sandstone and deposits of coal . The town is on several fault lines , the main one being the Vigo Fault , a branch of the larger Eastern Boundary Fault , which runs from Birmingham to <unk> . On the western side of the fault , in the area of Brownhills Common , the marl is over 1 @,@ 000 feet ( 305 m ) thinner than on the eastern side , bringing the coal seams significantly closer to the surface . The presence of the faults and the effects of mining mean that subsidence has been a major problem in the area for many years . 
