ORIGIN OF THE PENNSYLVANIA ANTHRACITE. 687 



beyond which they advanced slowly, as shown by changing type 

 of rocks, the chemical change should have been almost complete, 

 especially in the eastern Middle and the eastern extremity of the 

 Southern field, which occupy that part of the area- in which the 

 coal marsh, in almost every instance, appears to have thrust itself 

 first upon the advancing delta. 



It is quite possible that when detailed study of the anthracite 

 areas in Arkansas and Russia have been made, the same explana- 

 tion may be found applicable there also, and that the anthracite 

 will be found near the old shore line, whence the marsh advanced 

 as new land was formed. John J. Stevenson. 



