The oceanic crust of the North Sea was subjected to a lot of stretching both in Permian and Triassic times, and later in the Jurassic. This stretching resulted in the North Sea collapsing in and also to large faults forming west of Hordaland and on the mainland. Austefjorden in Sund follows one of these faults.
Mangerite is a rock type that was first made famous in a treatise by the Bergen geologist Carl Fredrik Kolderup in 1903. The rock type got its name from the place where it was found, and has made the Mangerud name well known around the world, at least among geologists.
Siggjo is a cone-shaped, volcano-like mountaintop in the part of Hordaland where one finds the best preserved volcanic rocks. The rock types originate from one or several volcanoes that spewed out glowing lava and ash. But, the shape of the mountain, as it appears today, formed later and by completely different forces.
In 1868 the first stone workers came to Rubbestadneset to take out the granite for the Skoltegrunns Pier, predecessor of the Skoltegrunns wharf in Bergen. Later granite was also taken out from the area, around Innværs Fjord and UransvågenN. The activity probably peaked around 1900, with over 40 men at work. 15 years later, it was finished.
The highest mountainous area on Stord, including Kattnakken, Midtfjellet and Stovegolvet, has more in common with the mountainous terrain on the mainland than in the low coastal landscape of Sunnhordland. The volcanic bedrock together with the erosive powers of nature has resulted in a unique plateau landscape.
220 million years ago, glowing hot molten rock masses intruded into fractures in the earth's crust in the outer parts of Hordaland. Some of these are believed to have reached the surface and formed lava flows, which since have been eroded away by wind and weather. But, most of these flows solidified into diabase sills before they got to the surface.