Dolerite-Sandstone Contact

Locality 9: The Salisbury Crags dolerite magma was intruded at a temperature of about 1200C into sedimentary rocks at close to 25C. At the contact the magma was chilled sufficiently rapidly to produce a glassy selvage a few millimetres thick. Further from the contact the magma cooled less quickly and crystals had time to form. There is a continuous increase in crystal grain size away from the contact and towards the centre of the sill, where crystals of olivine, plagioclase and clinopyroxene reach 3 millimetres or so in size.

Close to the contact the sedimentary rocks have been baked, producing recrystallisation and induration. This is perhaps not particularly evident at this location. [Closer]