1. Is the so-called “Thick Freeport” coal combination of the Upper and Lower Freeport beds, or an abnormal development of the Upper Freeport? Coal Mining Institute of America;Affelder,1920
2. Arndt, H.H., Wood, G.H., Jr., Danilchik, W., 1963. Geology of anthracite in the southern part of the Trevorton quadrangle, Northumberland County, Pennsylvania. U.S. Geological Survey Coal Investigations Map C-48.
3. Cannel coal in the United States. U.S;Ashley;Geol. Surv. Bull.,1918
4. Further applications of coal petrography;Benedict,1966
5. The Development of Coal Petrology in North America;Berry,1967