THE STORY OF OUR ROCK FOUNDATION 55 



of the coal mines. The rocks of the Devonian and Mississippian 

 are older than the Pennsylvanian but are not exposed in the state 

 nearer than its western side near Rock Island. They are found 

 nearer Chicago, in Wisconsin just north of Milwaukee, and also 

 in southwestern Michigan. Remnants of the Devonian rocks 

 are preserved occasionally in the cracks and crevices of the 

 Niagara limestone in this immediate vicinity. 



