DUNKARD FORMATION 231 



is separated from it by an interval of unknown rocks, apparently shale 

 with some limestone. It is in about the position of the Upper Wash- 

 ington limestone of Pennsylvania. 



This stratum is important, inasmuch as its top is the dividing plane 

 between the two divisions of the Upper Barren Measures or Dunkard 

 formation. Almost all of the Dunkard in Maryland falls in the lower 

 division or Washington County group of Stevenson, while the upper or 

 Green County group of Rogers is represented in Maryland by only the 

 65 to 90 feet of strata overlying this, and which cover an area of only a 

 few acres. 



Jollytown coal (60). — A thin seam of coal is found about 25 feet above 

 the outcrop of the Upper Washington limestone. It is apparently in 

 the stratigraphic position of the Jollytown coal of Green county, Penn- 

 sylvania. 



Jollytown limestone (61). — A limestone of apparently no very great 

 thickness is found about 15 feet above the Jollytown coal. It is in the 

 position of the Jollytown limestone of Pennsylvania. 



Above this limestone there are no good exposures, and not more than 

 50 feet of strata are preserved in Maryland. The highest bed is a sand- 

 stone which caps the hill east of Borden shaft. 



Conclusions 



The detailed comparisons given in the preceding pages show that the 

 various members of the Coal Measures of Maryland closely resemble 

 those found in Pennsylvania and West Virginia. They clearly demon- 

 strate the fact, if any such demonstration is necessary; that the various 

 beds of the Coal Measures have a wide geographical extent, and that 

 the individual coal beds possess certain marked physical characteristics 

 that can be readily distinguished over wide areas. The similarity of 

 sequence of the various members of the coal series is so striking and the 

 faunal and floral characteristics so marked that the determination of the 

 horizons of the several coal seams can be made with remarkable accuracy. 

 In the lower formations of the Coal Measures it has been possible to 

 establish this identity with the Pennsylvania and West Virginia deposits 

 on the basis of actual continuity of the beds, although this is not possi- 

 ble in the higher members of the series. The sequence of deposits and 

 faunal and floral characteristics are such, however, that very little doubt 

 can exist regarding their equivalency. 



The following table shows the sequence of Carboniferous and Per- 



XXXIV— Bull. Geol. Sbc. Am., Vol. 13, 1901 



