Siljan (lake) in the center of the ring, distant from the ring sediments and from Gravberg-1. This well went to a depth of . The hole produced gases and oily magnetite sludge similar to those found in Gravberg-1. Siljan (lake) Siljan, in Dalarna in central Sweden, is Sweden's sixth largest lake. The cumulative area of Siljan and the adjacent, smaller lakes Orsasjön and Insjön is . Siljan reaches a maximum depth of , and its surface is situated above sea level. The largest town on its shore is Mora. The lake is located around the southwestern perimeter of the Siljan Ring (Swedish:
Siljan Ring by rocks of the Llandovery series (Lower Silurian). During the last ice age the area was covered by a thick icesheet. The bedrock was sculpted by the ice, with the softer Palaeozoic sedimentary rocks being preferentially eroded. These erosional hollows are now occupied by lakes Siljan, Orsa, Skattungen and Ore. In accordance with theories about abiogenic petroleum (that hydrocarbons can be formed without involving material from dead plants and animals), astrophysicist Thomas Gold suggested that there might be major deposits of oil and natural gas in the area. Drilling was carried out in the late 1980s and early 1990s but