Burrows are fossil footprints from living beings activity into the sediment. They’re quite common in the sandstones in Bages district. Usually burrows look like an earthworm or branches of plants. They were originated by the dig of animals as crustaceous or bivalves that lived or searched food into the sediment. The sand filled in again the inner galleries and consolidates to be a burrow. The filling material could be laid down by the animal that dug it as well.
Some animals protect the galleries they dig with own secretions. If so, there are two types of materials, the external layer and the refill that can easily be removed. If the refill is lost, then the surfaces of the old galleries are displayed. As a result of the study of such surfaces, we know that similar to present crabs lived in the sea of Bages in Eocene period. These crabs cover the walls of their galleries with a layer of excrements which prints remain in the sand.
The 1st photo displays burrows in sea sandstone from Les Brucardes (Sant Fruitós de Bages), the 2nd one in continental sandstone from Collbaix (Manresa). In 3rd photo there is a cross of burrows and in 4th photo a curved burrow, both parallel to the stratification in marine sandstones in the valley of Santa Creu (Pont de Vilomara i Rocafort). The 5th photo shows recent burrows, from August-09, in the mud next to stream of Mura or St.Esteve before the merger with river Llobregat.