The flat-lying Paleozoic formations are transected by numerous steeply dipping joints. Joint planes vary from 30 cm to more than a metre and the spacing increases with increasing bed thickness. Numerous closely spaced joints commonly occur close to faults and are parallel to them, suggesting a genetic relationship between the joints and faults. Joints in carbonate rocks have been commonly widened by solution. Joints are commonly filled by calcite with minor pyrite, barite, celestite, and gypsum (Williams 1991). Precambrian rock formations form a complex pattern of joints and folds.

The entire region is transected by numerous steeply dipping normal faults and fault zones which have relative vertical displacements exceeding 785 metres in places. Identification of faults and fault zones is accurate in areas of bedrock outcrops; in areas of thick drift, the exact location of faults is not as precise as their location has to be interpolated from adjacent areas aided by the use of drillholes, geophysical survey data and fault-controlled topographic features.