cob·ble·stone /ˈkɑbəlˌston/
  圓石,鵝卵石
  Cob·ble·stone n. A large pebble; a rounded stone not too large to be handled; a small boulder; -- used for paving streets and for other purposes.
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  cobblestone
       n : rectangular paving stone with curved top; once used to make
           roads [syn: cobble, sett]