Cearan, or Ceirin, from ciar, black, was the name of one of the twelve Irish bishops whom St. Patrick consecrated.  He betook himself to solitude in a place surrounded with bogs in Ireland, called from him Saiger, or Sier Kieran; but a tribe of disciples followed him, and a monastery arose; so, in search of loneliness, he fled to Cornwall, where he lived in a cell, and taught the inhabitants so much, that they ascribed to him even their knowledge of mining; and the 5th of March, his day, was considered as the tinners' holiday, in honour of their patron saint. (History of Christian Names, Yonge, 1884)