758 FLORAL ZONES OF THE POTTSVILLE FORMATION. 



been remarked above, marine animal fossils are ver}^ rare in the ter- 

 ranes of the Pottsville along the eastern margin of the trough, the 

 usually abundant plant fossils constitute the chief evidence on which 

 correlations, in this region at least, must be based. 



The primary result of this work should be the paleontologic defini- 

 tion, if such is practicable, of the Pottsville formation, and the estab- 

 lishment of a paleontologic section which shall constitute the type 

 section of the formation, for comparison and reference in the study 

 and correlation of other middle Carboniferous phytiferous terranes 

 in the Appalachian province. Two other, largelv concomitant, results 

 that are either economic or scientific in their nature have also been 

 reached in the process of the elaboration of the fossil plants of the 

 formation in th(^ typical region. The first, of some economic interest, 

 is the correlation of groups of beds, or of individual coals wrought 

 in disconnected or somewhat isolated portions of the Southern Anthra- 

 cite field. The other, which concerns the question of general geologic 

 correlation, is the acquisition of data for the determination of the age 

 of the Pottsville formation — i. e., (a) the time interval represented 

 by the tvpe section, and (/>) the e(|uivalents, in a broad sense, of the 

 formation in other basins of this province and in other parts of the 

 world. Incidentally, also, through the discovery in the Pottsville of 

 floras already more or less completely known from isolated and uncor- 

 related terranes in other regions of the United States, the way is 

 opened to the proper reference and correlation of those terranes 

 with the Pottsville, or with portions thereof. However, in this report 

 no special eflort will be made to correlate the formations of this age 

 in the bituminous regions, except in certain special or important 

 cases. Such a work of general correlation will be more naturally 

 and eft'ectively done in connection with a general study of the floras 

 of the supposedly contemporaneous formations in the Appalachian 

 trough and of their relations to the tvpical Pottsville, a work that of 

 necessitv is dependent on and consequent to that now in hand. 



In this report the details of the geolog}' of the Southern Anthracite 

 field are coiisidei'ed only to the exttMit to which they are concerned in 

 the ascertained occurrence, distribution, or relation of the fossils exam- 

 ined. Beyond a general description of the field, the stratigraphic data 

 are largely confined to the ori(nitation of coals or plant beds, or to the 

 dcHnition of the formations in certain sections. The details relating 

 to the areal geologv are limited, first, to questions of the area of cer- 

 tain coals as identified and correlated at different ])()ints liv means of 

 the fossils, and, second, to the correction of certain areal and strati- 

 graphic errors in the existing maps, especially in those relating to 

 the western part of the field. These errors were discovered in the 

 course of paleontologic investigation and were worked out b\' the 

 combined methods of stratigraphy^ and paleontology. 



