Barrett, O. <br/><br/>
Mineral resources in illinois in 1917 and 1918. 

 - Illinois-US :   Illinois Mioning Investigations,   1922. 
 - páginas 28-112 
 - Irregular 
 - No. 38 (1922) 
 - State Geological Survey. Bulletin ;   no. 38 .
 - Department of Registration and Education. .