684 THE JOURNAL OF GEOLOGY. 



mie coals on the western side of the great plains, in New Mexico, 

 Colorado and Wyoming can hardly have undergone any material 

 change since the final burial ; otherwise the strange variations 

 in composition would be inexplicable, the difference in con- 

 dition as to character of rocks and degree of disturbance being 

 insufficient. 



Twenty years ago the writer, while connected with the Ohio 

 Survey, reached the conclusion that the marsh, from which sprang 

 the several beds of the Upper Coal group, originated at the east ; 

 two years later he was led to assert that the coal beds were 

 formed as fringes along the shore of the Appalachian basin. If 

 this be the true doctrine, there should be found in northeastern 

 Pennsylvania, 



First. A vastly greater thickness of coal than in other por- 

 tions of the basin. 



Second. A greater advance in the conversion of vegetable 

 matter into coal, owing to the longer period elapsing prior to 

 entombment. 



As to the first condition, there can be no doubt. A compari- 

 son of the several divisions of the Coal Measures as they appear 

 in the several basins of the state illustrates it well ; but such a 

 comparison would be tedious here, and only the Lower Coal 

 group of the Pennsylvania series is used (that lying between the 

 Pottsville conglomerate below and the Mahoning sandstone 

 above). 



In the Anthracite Strip this group shows in the several fields, 

 from south to north, as follows: 



Cumberland Field, bituminous, - - 13' 



Broad Top Field, bituminous, - - - 14—15 ' 



Southern Anthracite, bituminous to anthracite, - i8'-6o' 



Middle and Northern Anthracite, anthracite, - 40 '-58' 



The thicknesses in the Bituminous basins are : 



First, ...... 21-23' 



Second, ------ 19'— 22' 



Fifth, ----- 8'6"-i3'4" 



The thicknesses, as given for the Anthracite Strip, are those 



