were placed in the enclosure's ditch and at other points within the monument, mostly in the eastern half. Stonehenge is therefore interpreted as functioning as an enclosed cremation cemetery at this time, the earliest known cremation cemetery in the British Isles. Fragments of unburnt human bone have also been found in the ditch-fill. Dating evidence is provided by the late Neolithic grooved ware pottery that has been found in connection with the features from this phase. Stonehenge 3 I (c. 2600 BC) Archaeological excavation has indicated that around 2600 BC, the builders abandoned timber in favour of stone and dug two concentric arrays of holes (the Q and R Holes) in the centre of the site. These stone sockets are only partly known (hence on present evidence are sometimes described as forming 'crescents'); however, they could be the remains of a double ring. Again, there is little firm dating evidence for this phase. The holes held up to 80 standing stones (shown blue on the plan), only 43 of which can be traced today. It is generally accepted that the bluestones (some of which are made of dolerite, an igneous rock), were transported by the builders from the Preseli Hills, away in modern-day Pembrokeshire in Wales. Another theory is that they were brought much nearer to the site as glacial erratics by the Irish Sea Glacier although there is no evidence of glacial deposition within southern central England. A 2019 publication announced that evidence of Megalithic quarrying had been found at quarries in Wales identified as a source of Stonehenge's bluestone, indicating that the bluestone was quarried by human agency and not transported by glacial action. The long-distance human transport theory was bolstered in 2011 by the discovery of a megalithic bluestone quarry at Craig Rhos-y-felin, near Crymych in Pembrokeshire, which is the most likely place for some of the stones to have been obtained. Other standing stones may well have been small sarsens (sandstone), used later as lintels. The stones, which weighed about two tons, could have been moved by lifting and carrying them on rows of poles and rectangular frameworks of poles, as recorded in China, Japan and India. It is not known whether the stones were taken directly from their quarries to Salisbury Plain or were the result of the removal of a venerated stone circle from Preseli to Salisbury Plain to "merge two sacred centres into