280 D. WHITE — DEPOSITION OF APPALACHIAN POTTSVILLE 



basin, added to the time required for the accumulation of the vegetable 

 matter in a great thickness of coal beds. The lapse of time is hardly 

 less forcibly demonstrated by the remarkable changes in the plant life. 



Summary of Appalachian Pottsville History 



From the data now available it is possible to sketch a portion of the 

 history of the Appalachian coal field during Pottsville time. It may be 

 outlined as follows : 



1. At the close of Mauch Chunk time there existed a broad, low coun- 

 try or great coastal plain bordering a vast expanse of shoals, ferruginous 

 mud flats and shallows extending across the greater part of the region of 

 the northern coal fields. The Pocono activity of erosion had subsided. 

 These great stretches of Mauch Chunk flats were marked by ripple 

 marks, sun cracks, reptilian footprints, and raindrops. There appears 

 to be no evidence of deep water in any considerable part of the northern 

 Appalachian basin at this time. 



2. These relatively quiescent conditions were followed by orogenic 

 movement, the lifting of the western and by far the greater part of the 

 Mauch Chunk above sealevel, while mountain-building took place to the 

 east, and, concomitantly, the eastern border of the Mauch Chunk shal- 

 lows was warped to form a relatively narrow trough, presumably flank- 

 ing the mountain region. It is possible that other, more gentle undula- 

 tions occurred, to the northwestward, remaining low arches or barriers 

 being more or less distinctly indicated (1) between the Eastern Middle 

 and the Northern Anthracite fields, (2) east of the Allegheny front in 

 Pennsylvania, and (3) along the Allegheny valley in western Pennsyl- 

 vania. Erosion was accelerated and rapid sedimentation, with some 

 redeposition of the Mauch Chunk coastal plain sediments, took place. 

 This was the earliest stage of the Pottsville. 



3. There was subsidence under loading with occasional intervals of 

 stability in which coals were formed. Westward transgression by the 

 sea resulted from the subsidence of the basin, with some warping and 

 angularity of stratification. In early Pottsville time marine invertebrate 

 faunas reached as far north as central West Virginia,* though it is prob- 

 able that the basin was still of no great width. 



4. Sedimentation and intermittent subsidence continued, with broader 

 encroachments during the latter part of the Middle Pottsville and Raleigh- 

 Bon Air time when the transgression passed the present western limits 

 of the coal field in Alabama and southern Tennessee and made great pro- 



*The fiiuaa of the lower Pottsville in the Southern Anthracite field is of a kind less conclusive 

 as to mai iue conditions. 



