Sorry about the link FLG - try this one.
http://ads.ahds.ac.uk/catalogue/adsdata/PSAS_2002/pdf/vol_094/94_001_027.pdf

"Chambered cairn" is the more normal term for monuments like Crarae. To expand on that a bit - Crarae belongs to a group of chambered cairns known as Clyde cairns because their distribution, whilst covering most of SW Scotland, centres on the Clyde estuary. There are about 100 Clyde cairns. (The references to "Clyde-Carlingford cairns" in the excavation report reflect the thinking of the early 1960s which has now been superseded.)

In many chambered cairns, there is a passage which leads to the burial chamber. What marks out Clyde cairns as a distinctive group is the absence of a passage.

The chamber (or, more normally, a series of them placed end to end) reaches the cairn edge where there are usually elaborate entrance arrangements including (as at Crarae) large stones (portals) and a facade.

Dating is difficult other than in very general terms as most excavations were done in pre-radio carbon days. In Scotland, it is generally accepted that the earliest chambered cairns date from the first half of the fourth millennium BC (4000 - 3500 BC).