It is not clear what material the inhabitants burned in their hearths. Childe was sure that the fuel was peat, but a detailed analysis of vegetation patterns and trends suggests that climatic conditions conducive to the development of thick beds of peat did not develop in this part of Orkney until after Skara Brae was abandoned. Other possible fuels include driftwood and animal dung. There is evidence that dried seaweed may have been used significantly. At some sites in Orkney, investigators have found a glassy, slag-like material called "kelp" or "cramp" that may be residual burnt seaweed.