Plate 177

Vein systems

Plate 177 shows the surface of a "cellular" or reticulated limestone, where the cells are outlined by crossing systems of veins. Veins are secondary structures due to precipitation of salts within fractures. This chemical cement is often harder than the fractured rock, which is removed first by weathering and erosion enhanced here by salt and wind action on a seashore. An inversion of relief thus occurs: cavities become protruding parts, as in the already discussed case of septaria. The trellislike patterns eventually end up in open frameworks through the complete removal of the original rock.

Paleozoic limestone, New South Wales, Australia.