The ultramafic rocks are probably Jurassic or Cretaceous in age, and constitute a spoon-shaped lopolith with a dunite feeder plug at the east end.
The lopolith lies with complete discordance upon plutonic and metamorphic rocks of complicated structural and metamorphic history, and is overlain concordantly by rhyodacite tuffs which are intruded by the granophyre and are in turn overlain concordantly by sedimentary rocks.
A stockwork of dykes of mainly jotunitic (monzonoritic) composition crosscuts the anorthosite bodies and the lopolith.
Origin
Early 20th century: from Greek lopas 'basin' + -lith.