48+ 



THE POPULAR SCIENCE MONTHLY. 



This arises mainly from defective work in the earlier years of the 

 survey, when men and methods were more or less on trial, and 

 from the demand for more detailed and accurate maps on which 

 to plat the geology of the coal and iron regions of the Appala- 

 chians, and the gold, silver, iron, coal, and artesian areas of other 

 sections of the country : 



