Complex sentence: Other volcanic activity occurred in the region farther east, on Hardy Peninsula and some surrounding capes and islands during the Miocene; potassium-argon dating has yielded ages of 18 and 21 million years ago.
Split into simpler sentences: Other volcanic activity in the region farther east, on Hardy Peninsula and some surrounding capes and islands. This volcanic activity occurred during the Miocene, potassium-argon dating has yielded ages of 18 and 21 million years ago.