In the Beartooth Mountains, the Madison Group represents an essentially uninterrupted sequence of sedimentation that began in Kinderhookian time and continuedinto the early Meramecian. This sequence is boundedbelow by an unconformity that separates it from the underlying Three Forks Formation of Late Devonian age andis terminated by an unconformity that separates it fromthe overlying Amsden Formation whose lowest beds weredeposited during Meramecian or Chesterian time