WHITE.] FLORAL ZONES OF THE POTTSVILLE FORMATION. 773 



PAIiEOXTOI^OGIC DIVISIONS OF THE FORMATIOX. 



An inspection of the table (p. 770) showing the distril)ution of 

 the plants Avithin the Pottsville formation itself in the Southern 

 Anthracite field shows that the species are essentialh' divided into 

 two g-roups. one of which is confined to the lower Lykens coals, or 

 the lower part of the formation, the other ])eing present in the upper 

 Lvkens coals, and the upper lieds of the formation as a whole. For 

 convenience in reference all the plants occurring at any point in the 

 Lower Lvkens group of coals are placed in the first list. It is not 

 impossible that a num])er of these will cvtMitually be found in the 

 upper division of the formation. However, so far as my observation 

 has gone, it appears that, except among the gymnosperms, but 3 

 to 5 of the 50 species of the older fiora are present in the Upper 

 Lvkens, while 3 others occur in beds of the same period in the 

 type section. If we next examine the distribution of the plants in 

 the several fossiliferous lieds of the type section at Pottsville, we find 

 that of the plants in beds A-D, i. e., 700 feet or more lielow the Twin 

 coal, all are common to the Lower Lykens coal group. In fact, all 

 but 3 or J: of the species represented in this division are included 

 in and mostly confined to the Lower Lykens group in the mining- 

 region. We may therefore safely conclude that the highest bed, D, 

 of this portion of the type section is not younger than the Lykens coal 

 No. 4, with which its species are mostly in connuon. This portion of 

 the tvpe section appears to l)e clearly contemporaneous with the Lower 

 Lvkens group. The two corresponding sections will, therefore, be 

 collectively included in what will be for the present designated the 

 Lower Lvkens division of the formation. Of the species in the 

 Upper Lvkens group, only 13 or 14, including 7 gymnosperms, 

 occur in the lower group, either in the type section or in the mining- 

 region. 



Passing again to that portion of the table relating to the type sec- 

 tion, we find that the distribution of the plants occurring over Lykens 

 coals Nos. 1-3 is conlined almost exchisively to beds H-L of that 

 section. The high degree of identity in the fioras and the bio- 

 logic evidence of the small l)alance of independent species unite in 

 showing that each of tin* several IkmIs in that portion of the type 

 section i> rcfcral»lt> to, and proba))ly lies within, the time interval 

 marked hy the UpptM' Lykens group of coals. We shall, accordingly, 

 in f urtherdiscussions, treat this group as belonging to an Upper Lj^kens 

 division. Of the \'2'> species of plants found in this division, l)ut 13 

 or 14, including the gynniosperms, are conunon to the Lower Lykens 

 division, while 1».5 are, so far as ol)served. confined to t\w Upper Lykens 

 division. 



There remain two Ncrticaily restricted portions of the type section 



