Sheet fractures and structures - Landforms and Geology of Granite Terrains - page 29

(c)

Figure 2.2. (c) Pseudobedding cutting across orthogonal fractures, at Heltor, Dartmoor, southwest England.

(a)

(b)

Figure 2.3. (a) Sketch of quarry face near Wudinna, northwestern Eyre Peninsula, South Australia, showing

en echelon arrangement of partings in complex sheet fracture. (b) Geological section through
the Pão de Açucar, Rio de Janeiro, Brazil.

At some sites radius of curvature increases with depth ( Fig. 2.1b). Most, though significantly not
all (see below), sheet fractures run roughly parallel to the land surface, being essentially horizon-
tal on summits and beneath valleys, but steeply inclined beneath hillsides (Figs 2.1 and 2.3b). At
many sites, however, the sheeting fractures are more steeply inclined than the land surface (Fig.
2.3c) while at others the hillslope truncates the partings (Fig. 2.3d). They also plunge steeply (up
to 70°) in the vicinity of major vertical or subvertical fractures, and some terminate against such
partings (Fig. 2.3e). Many so-called sheets are attenuated wedges, though it is in some instances
difficult to distinguish between original geometry and modifications due to weathering and