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124 THE DEVONIAN AND CARBONIFEROUS. [bull. 80. 



false conclusions, could be adjusted by compromise or by readjustment 

 of nomenclature. In the case of fossiliferous zones the real difficulties 

 became more apparent as the final adjustments were attempted. 



Mr. Stevenson, 1 in 1878, said that the Upper Devonian rocks of south- 

 west Pennsylvania, underlying the Vespertine or Pocono sandstone, 

 are well exposed in the gaps of the Conemaugh River through Laurel 

 and Chestnut Ridges. He gave a general section of these rocks as ob- 

 served in the gaps, as follows : 



Feet. 



1. Shales and thin gray sandstones HO 



2. White to reddish-gray sandstones with some shale 70 



3. Reddish-gray micaceous sandstones with red to gray and olive shales 150 



4. Red to gray shaly sandstones with variegated clays and shales 2C0 



500 



After a description of the rocks, and a discussion of their relations, 

 he concluded by saying, that, " as the lithological characters of these 

 rocks are much like those of the Chemung, and their fossils, both 

 animal and vegetable, are unquestionably of Chemung age, the rocks 

 themselves must be Chemung, probably representing the Lower Che- 

 mung;" and that " the great Catskill group has so far thinnei] out that 

 it is represented only by its upper or gray member, the Vespertine of 

 Pennsylvania." 



The Pennsylvania reports published iu 1880 gave little indication o 

 the true nature of the errors of correlation of the Upper Devonian. I 

 the Report of Progress G 7 , 2 the imperfection of the theory of " persi 

 ent parallelism of strata" became evident. The author classified th» 

 deposits examined as follows : 



Pottsville Conglomerate, with 8 feet of slate and sandstone below it in a section at 

 Susquehanna Gap. 



Mauch Chunk Shale, No. XI, 150 feet. 



Pocono group, No. X, 353 feet. 



The Pocono-Catskill group, 400 feet thick near Loretto. 



Catskill, No. IX, varying in thickness from 1,800 to 4,500 feet. The base of the Cats- 

 kill is fixed as the lowest horizon at which the scales, teeth, and bones of 

 HoloptijcMus occur. 



The Catskill-Chemung group, section between Rupert and Catawissa, 1,077 feet. 

 The base of this group was the lowest red bed. 



Chemung, near Rupert, 2,443 feet thick. 



Hamilton, at Little Fishing Creek, made up as follows: 



Feet. 



Genesee slate 275 



Tully limestone.. 50 



Hamilton 1 400 



Marcellus shale 410 



This is called the " Northern type." 



•Stevenson, J. J.: The Upper Devonian rocks of southwest Pennsylvania. Am. Jour. Sci., 3d 

 ser., vol. 15, 1878, pp. 423-430. 



2 The geology of the Susquehanna River region in the six counties of Wyoming, Lackawanna, Lu- 

 zerne, Columbia, Montour, and Northumberland, by L C. White, 1883. 





