On some noritic dikes from Ørsdalen.

When the writer, some years ago, mapped the swarm of young, WNW-striking dolerite dikes which dissect the Precambrian igneous complex of the Egersund region (SW-Norway), the question arose how far these extend into the gneisses bordering the stiff anorthosite masses in the interior of the country. In this connexion, two days of field work were devoted to a reconnaissance of Ørsdalsvatn, a 16 km long lake running in a straight line from Bjerkrem towards NE and of the Ørsdalen valley, a 10 km long extension of the same narrow trough, cut by the glaciers deep down into the peneplain. Whereas no dolerites belonging to the Egersund swarm could be detected, neither in place nor as pebbles in the rivers, the attention of the writer was called to several, hitherto unrecognized, noritic dikes, which deserve a short description.