SCHOPF, James M. <br/><br/>
Field description and sampling of coal beds / 
by James M. Schopf. 
 -- Washington :   United States Government Printing Office,   1960 
 - P. 25-70 p., [14] h. de lam. -- 
 (Geological Survey Bulletin  ;  1111-B).
<br/><br/><label>Subjects--Topical Terms: </label><br/>Geología
<br/><br/><label>Universal Decimal Class. No.: </label>55