550 IOWA ACADEMY OF SCIENCE Vol. XXV, 1918 



A point of special industrial interest is the fact that more than 

 95 per cent of the available coal tonnage in the Eastern In- 

 terior field is confined to horizons in the Des Moines Series. This 

 h another genetic factor linking it with the Western Interior 

 field where 98 per cent of the coal is also found to be restricted 

 to the same series. 



