DeWolf, F.W. <br/><br/>
State geological survey. Bulletin. Separata ;   no.20 

 - Illinois-US :   Illinois state geological survey,   1915. 
 - páginas 9-157 :   Ilustraciones blanco y negro 
 - Irregular 
 - No.20 (1915) 
 - State geological survey. Bulletin. Separata ;   no.20 .
 - University of Illinois. .