Sentence:  ‘In many ways modern art was a culture of the beach. They say it's the light, the special quality of quartz in the <WSD>Permian</WSD> rock.' 
Meaning of the word marked with <WSD> tags:  Pertaining to the last geologic period of the Paleozoic era; comprising the Cisuralian, Guadalupian and Lopingian epochs from about 280 to 248 million years ago. (from 19th c.)