WHITE.] SUMMARY OF CONCLUSIOISrS. 915 



series in the northern bituminous basins. Furthermore, the plants 

 from the thinner coals in the tj^pe region, in some cases about 100 

 feet or more lower than the ''Buck Mountain" (Twin) bed, and close 

 to or partl}^ within the top of the upper dense complex of conglomer- 

 ates, with which the formation culminates, are also clearly paleonto- 

 logically referable to the Lower Coal Measures, the}' being- comparable 

 to the lowest floras a})ove the Homewood sandstone in the bituminous 

 basins. In other words, the conventional stratigraphic boundary 

 between the Pottsville formation and the Lower Coal Measures is, in 

 the Southern Anthracite field, slightly higher than the paleontologic 

 boundary. The paleontologic boundary appears to lie close within 

 the outslvirts of the upper plexus of conglomerates which form the 

 most conspicuous feature of the formation from the Pottsville Gap 

 westward. 



8. In the central districts of the field the formation probably attains 

 its maxinnun thickness of a little more than 1,200 feet. Westward it 

 thins very gradually on the whole, the thickness at Rattling Run Gap 

 being 1,100 feet. Eastward it appears to I'apidly decrease to about 

 830 feet at Tamaqua, and perhaps less than 800 feet at the Lansford 

 railroad tunnel, though it seems to expand somewhat to the east- 

 ward of this point near the apex of the field. Little, if anj", diminu- 

 tion is observed within this field in passing from south to north. 



9. The fossil plants of the Pottsville formation in the type region 

 exhibit a rapid development and series of changes or modifications, 

 which, if treated with great S3^stematic refinement, are of high strat- 

 igraphic value. With the exception of the species from the topmost 

 beds of the formation, the ferns are, in general, readily distinguished 

 specifically from those at the base of the Lower Coal Measures, or 

 Allegheny series, as recognized in the northern United States, while 

 the floras of the lower portions of the section are found, in passing- 

 downward, to b(^ar still less resemblance to those of the Lower Coal 

 Mcasurt\s. Two principal divisions of the formation, to which com- 

 paratively few fern species are conmion, are recognized. These 

 divisions, which coincide with the natural grouping of the Lykens 

 coals, are here termed the Lower Lykens division and the Upper 

 L3kens division. A portion, including about 200 feet of the type 

 section between these two paleontologic divisions, contains a mixed 

 flora, and has been temporarily designated the Lower Intermediate 

 division. A portion of the type section, at about 200 feet below the 

 Buck Mountain coal, contains floras largely characteristic of the Potts- 

 ville, l)ut in association with a number of the earliest Coal Measures 

 species. This is temporarily termed the Upper Intermediate division. 

 The Lower Lj'kens division includes two floral zones, (1) that of the 

 lowest beds, up to and including the roof shales of Lykens coal No. 5, 

 and (2) that of tiie vicinity of Lykens coal No. 1. The first contains 



