UPPER PRODUCTIVE COAL MEASURES. PP. 23 



subsidence is of importance in furnishing a cause for the 

 great difference shown in the flora of the Pittsburg and 

 Waynesburg Coals. In order to bring out more distinctly 

 this feature we give three graphic sections of the Upper Pro- 

 ductive Measures, as found at three points, which may be 

 taken as fairly representative of the whole.* 



It must be noted that these limestones show no marine fos- 

 sils, and none of the shells so abundant in the limestones 

 up to the middle of the Lower Barren Measures are found 

 in them. The only organic remains which they contain are 

 a few minute bivalve crustaceans. They vary a good deal 

 in composition, but are usually impure. They are most 

 probably of fresh-water origin, A portion of themi may 

 have been formed in brackish water. These features all in- 

 dicate that an important change in the physical features of 

 the country took place towards the close of the period in 

 which the Lower Barrens were formed. 



We see from the sections, that in Monongalia Co. W. 

 Va. we get between the Pittsburg and Waynesburg Coals 

 88 feet of limestone ; at Wheeling, W. Ya., not including 

 the intercalated shales, 150 feet ; and in Greene Co., Penn., 

 119 feet. 



According to the geologist's method of reckoning time 

 the formation of so much limestone, and of such a mass of 

 fine shales, requires a long period, and this, combined with 

 the amount of subsidence which must have occurred over 

 wide areas, would fully explain that change in the facies of 

 the flora which we find exhibited in the plants of the 

 Waynesburg Coal bed. This change will be better under- 

 stood after an examination of the fossils found associated 

 with that coal seam. 



The following section of the Waynesburg coal bed is 

 given to show the mode of occurrence of the plants. The 

 bed is one of the most important and persistent of the 

 Upper Coal beds, covering as it does an area in West 

 Virginia and Pennsylvania of at least 15,000 square miles. 

 Where best developed it contains fully 8 feet of coal, and 



* See Sections and Figs. 1, 2, 3, at the end of this chapter. 



