1841
The formation and geological folding of the Harz hills began during a prominent phase of the Palaeozoic era , in the course of the Hercynian mountain building of the Carboniferous period , about 350 to 250 million years ago .
 location: Harz; location: Hercynian; location: Carboniferous
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 location: Harz; location: Hercynian; location: Carboniferous