Quartz sandstone with vertical burrows, Cambrian Pipe Rock

From road-cuts near Skiag Bridge, Loch Assynt, and south of Loch Glencoul.

Outcrop

Quartz sandstone with vertical burrows, Cambrian Pipe Rock
In this outcrop, part of the rock has been stained purplish brown by iron and manganese oxide. The staining has picked out the bedding in the sandstone (horizontal stripes), and reveals very clearly the vertical white sand-filled burrows that are the characteristic feature of the Pipe Rock. The penknife is 9 cm long.

  Quartz sandstone with vertical burrows, Cambrian Pipe Rock
Here we are looking down on a bedding plane of the pipe rock, which shows circular hollows. These are the tops of burrows, which have weathered out because they are slightly less strongly cemented than the rest of the rock.

Hand specimen

  Quartz sandstone with vertical burrows, Cambrian Pipe Rock
The cut surface of this hand specimen of Pipe Rock shows sections of the vertical "pipes", which stand out in white against the purple-stained matrix of the sandstone. The bedding runs horizontally across the specimen. The pipes look a little crumpled, perhaps because the sand was compacted before it became fully hardened into rock.

The pipes are given the scientific name Skolithos, and are thought to be made by worm-like creatures that lived upright in the burrow and fed by filtering food from shallow water above the sediment surface.

Thin section

Quartz sandstone with vertical burrows, Cambrian Pipe Rock
This view shows a section across the edge of a "pipe". On the left, the "pipe" consists of slightly finer sand particles with less dark material in the matrix. On the right, the sandstone matrix contains more abundant oxide material. This dark material is responsible for the purple-red colour in hand specimen and outcrop.

Plane polarized light, field of view 5 mm across.

D.J. Waters, Department of Earth Sciences, May 2003