When the inclined position is produced by an uplift of the strata, along a given line, so that they dip in opposite directions, this line is called an anticlinal axis, as at [Fig. 54]. If, however, the strata are fractured along this line, as at b, the fracture becomes a valley of elevation.
If depression take place along a given line, as at c, the strata will dip towards this line, and it will be a synclinal axis. The depression will be a valley of subsidence. A synclinal axis would also be produced by an elevation of the strata, as at d and e, on each side of it, and the valley thus produced is one of elevation.
When successive sets of strata, as f and d, [Fig. 53], are not parallel, they are said to be unconformable.
