Parallel cracks in the limestone layer below El Pont Vell

The Pont Vell (= Old Bridge) on the Cardener river, in Manresa, was built above a resistant layer of nummulitic limestone rock. This layer of limestone slightly tilts to the north according to the general slope of the strata, therefore, it outcrops to a wider extent on the southern shore, that of La Guia. The nummulitic limestone layer of El Pont Vell belongs to the member Tossa (for La Tossa de Montbuí [Anoia] where it was described first), the highest and most modern (from Mid Eocene, about 37-38 million years) of the geological formation Santa Maria (for Santa Maria de Miralles [Anoia]), of marine origin.

The limestone outcrop on the south bank of El Pont Vell also stands out for its series of parallel to the slope cracks. The own weight of the rock must be responsible for this geometric network of fractures. The same arrangement of the rock and the same parallel to the slope pattern of cracks is repeated in the pool of La Llosa of the stream of Guardiola.

On the north bank of El Pont Vell, the scarce uncovered stretch of limestone is often under river water. That’s why the limestone in the north bank displays potholes.

[photos Jordi Badia]