Even though the vast majority of Icelandic toponyms are native and clearly interpretable (for example Ísa-fjörður ice fjord, Flat-ey flat island, Gull-foss golden waterfall, Vatna-jökull water glacier, Reykja-vík bay of smoke, Blanda the mixed (river) (which is formed by the confluence of different rivers)) there are some that up to now have resisted any plausible interpretation, even in the light of the Celtic languages. For example, Esja (a mountain on Kjalarnes), Ferstikla (a farm near Hvalfjörður), Vigur (an island in Ísafjarðardjúp), Ölfus (an area of Árnessýsla, traversed by the river Hvíta-Ölfusá), Tintron (a volcanic crater in Lyngdalsheiði), Kjós (the area that gives its name to Kjósarsýsla), Bóla (a farm in Skagafjörður) and Hekla (a famous Icelandic volcano). Such toponyms pose numerous problems, but the main one can be stated in a very simple question: if they are neither Icelandic nor Celtic, which language do they come from? Perhaps they have been taken from a language (or languages) of unknown ethnicity, or perhaps (and this is a fascinating though highly improbably hypothesis) these names are a sign that Iceland was already inhabited not only before the landnám, but even preceding the arrival of the first Irish hermits. But who were these people? Some scholars, such as Árni Óla, have concerned themselves with the question, attempting to demonstrate this hypothesis, which would force a complete rewrite of Icelandic history. Others have asserted that since Icelandic is an imported language, such names could in reality be traced back to some unknown substrate of Norwegian (comparisons have consequently been made with Northern Sami and other Uralic languages), and have therefore been transplanted to the island by colonists who originated from parts of Norway where such substrate languages would have still been present. Naturally, there have been numerous attempts to explain the names in terms of Icelandic: Kjós, for example, could come from the root of the verb kjósa, and therefore mean the chosen land; moreover, there is also the common Norwegian surname Kjus. Bóla could be simply ból dwelling, habitation, from the root of the verb búa inhabit, present in many names of farms such as Aðal-ból main farm.