John Thurnham termed these "unchambered" barrows,[10] while the archaeologist Stuart Piggott favoured the term "earthen" barrows for them.[11] Ian Kinnes instead used the term "non-megalithic barrows".[12] These long barrows might have used timber because stone was not available.[1] Some classificatory systems, such as that employed by the United Kingdom's National Monuments Record[disambiguation needed], do not distinguish between the different types of long barrow.[13]