440 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



northwest appears to be rather thicker. The group is overwhelmingly conglomeratic, the 

 lower beds consisting of poorly assorted, locally subangular detrital material, which varies 

 in size not only at different localities but at a single locality,*'^* and is interstratified with some 

 mud beds and coals. The higher conglomerates are more exclusively quartzitic, the pebbles 

 less variable and generally better rounded, and the top portion of the column consists of a 

 plexus of most massive, fairly regular, well-assorted quartzose conglomeratic material, in 

 which occur several thin coals. The group is underlain at Pottsville by 400 feet or more of 

 irregular, poorly assorted puddingstone conglomerates, locally unconformable on brownish-red 

 and olive-green muds, which by some authors are included in the Pottsville and which no 

 doubt belong to the Pennsylvanian. This transitional series, which technically lies beneath 

 the topmost stratum of red shale, the arbitrary lower boundary of the Pennsylvanian, quickly 

 disappears in passing north. The lowermost Pennsylvanian in the southern portion of the 

 anthracite regions (not deposited in the eastern middle and northern anthracite fields) bears 

 some evidence of fluviatile deposition. The beds are, in general, unusually variable in thick- 

 ness, and the stratigraphy of the coals shows a lack not only of parallelism but, to a certain 

 extent, of synchronism. Consequently the correlation of the coals is far from complete or 

 satisfactory. Little progress has been made in correlating the coals of the northern anthracite 

 field with those of the basins to the south. 



The fossU plants of the Pottsville in the type region exhibit a rapid development and 

 series of modifications which are of high stratigraphic value. With the exception of the species 

 from the topmost beds, the ferns are, in general, readily distinguished specifically from those 

 at the base of the "Lower Coal Measures,""* or Allegheny formation, as recognized in the 

 northern United States, while the floras of the lower portions of the section are found, in 

 passing downward, to bear still less resemblance to those of the "Lower Coal Measures." On 

 the paleobotanic basis the type section is parted into four divisions, as follows : 



L A lower division, 700 feet in thickness, called the "Lower Lykens division *°^'' because 

 it includes (paleontologically) the lower group of Lykens coals (Nos. 4-6 and "0") as mined 

 in the western portion of the field. This, the older Pottsville, includes two zones-^(a) the 

 Neuropteris pocahontas zone, including Lykens coals Nos. 5, 6, and "0," and contemporaneous 

 with the Pocahontas formation (basal Pottsville) of the southwestern Virginia region ^^^' '^*' ^^° 

 (J 17), and (b) the Mariopteris pottsvillea zone, probably contemporaneous with the Quinni- 

 mont formation ^ of the central Appalachian region. Both are included in the time interval 

 covered by the Lee formation, which to the south is represented, according to the fossil plants, 

 by the Lookout sandstone and a part of the Walden sandstone in Tennessee and Alabama and 

 which constitutes the lower Pottsville. 



2. Above the "Lower Lykens division" is a relatively barren series, about 130 feet in thick- 

 ness, which the writer ^^^° for temporary convenience called the "Lower Intermediate division." 

 It contains a mixed flora and is regarded as lying at or near the horizon of the Raleigh sand- 

 stone, the topmost division of the lower Pottsville in the Virginian region, as will be explained 

 farther on. 



3. A zone of about 200 feet, extending, roughly, from 370 to 570 feet below the top of the 

 formation, contains the floras characteristic of Lykens coals Nos. 2 and 3, farther west, and has 

 therefore been termed by the writer ^'^'^ the "Upper Lykens division." It is provisionally 

 referred to the middle Pottsville, which embraces the Sewell formation, or New River group of 

 I. C. WhitCj^"'* as recently proposed by him. The latter term, as restricted, is conducive to 

 confusion, not only because of the economic development of the lower Pottsville coals along 

 New River, but also on account of its former application to the Pocono coals (basal Mississip- 

 pian) , which are likewise commercially exploited along New River. 



« "Lower Coal Measures" as sometimes applied in the anthracite fields of Pennsylvania; not the series of that 

 name in Canada or Europe. 



b See Raleigh, Pocahontas, Tazewell, Bristol, Eatillville, and Briceville folios, Geol. Atlas U. S. 



