The Burnley Coalfield is the most northerly portion of the Lancashire Coalfield. Surrounding Burnley, Nelson, Blackburn and Accrington, it is separated from the larger southern part by an area of Millstone Grit that forms the Rossendale anticline. Occupying a syncline, it stretches from Blackburn past Colne to the Yorkshire border where its eastern flank is the Pennine anticline.