388 HISTORICAL GEOLOGY 



deposits in eastern United States. Why should their outcrops, as 

 shown in the map (Fig. 401), be so different in shape from those 

 of the Cambrian system? 



7. In Rhode Island the coal is very hard and graphitic. From 

 this .fact what do you suspect with reference to the structure of 

 the Coal Measures in that district ? 



8. From which variety of coal could illuminating gas be made 

 to the best advantage, and why ? 



9. Of the mineral products which you have studied thus far, 

 which most resembles coal in method of occurrence, iron, copper, 

 or zinc ? 



10. Iron ore is not infrequently deposited in bogs at the present 

 time. That being true, in what part of the United States might 

 such ore be expected in formations of Pennsylvanian age ? 



