Time lines: Sketches record archaeological dig on Orkney

Archaeological excavations on Orkney have been documented in a series of sketches and watercolours.

Karen Wallis was artist in residence on the Ness of Brodgar dig, which was carried out over several weeks earlier this year.

Since 2002, Neolithic buildings, artwork, pottery, bones and stone tools have been found in the area.

Wallis's Ness of Brodgar Sketchbook Journal records the latest dig and the people who took part in it.

These included archaeologists from the University of the Highlands and Islands and volunteers.

This year's dig uncovered a mysterious stone structure.

Archaeologists said it was found buried under what they described as Scotland's "largest Neolithic rubbish dump".

The layout of the stone slabs, known as orthostats, is unlike anything previously found on the islands.

Archaeologists are also mystified as to why the structure was covered over by a huge midden.

They have speculated that it could possibly be a chambered tomb.