WHITE] COMPOSITION OF THE POTTSVILLE FORMATION. 765 



Pennsylvania Railroad bridge, occur the most massive, rigid, densely 

 quartzitic, regularlv bedded, and persistent conglomerates of the entire 

 section. These conglomerates constitute a close group or plexus of 

 ponderous ledges in which the formation culminates. The}" usuall}^ 

 form the conspicuous beds in ever}^ exposure of the formation, and in 

 every break in Sharp Mountain through which the waters of the basin 

 find escape these steeply inclined ledges appear as jagged, irregular 

 teeth, picturesquely defining the jaws of the gap. Exceptions to this, 

 however, are Lorberry and Fishing Creek gaps, at which the entire 

 Pottsville formation appears to be absent. Usually they also form 

 the crest of the mountain, although, as was remarked above, the lower 

 conglomerates predominate in the older exposures. It may be noted 

 in this place that these uppermost white or light-gray conglomerate 

 plates, which in both their lithologic and their paleontologic characters 

 are distinctly comparable to the Homewood sandstone in the bituminous 

 basins, appear to have the greatest geographic extent and regularity 

 of all the strata in the formation. Thev are amonsthe few individual 

 beds which, although varying in thickness and in relative intervals, 

 may be traced to sections in distant portions of the same field. 



As shown in Pis. CLXXXI, CLXXXII, the type exposure at Potts- 

 ville exhibits a number of thin coals, none of which are profitably 

 workable in this vicinity, although most of them have been diligently 

 prospected. The exposure nearly 800 feet below the Twin bed appears 

 to have been followed b}' a drift for some distance above the wagon 

 road on the east side of the gap, while another coal, about 400 feet 

 below the Twin, has been somewhat extensively tested, not only farther 

 north in the same gap, but at two or more levels in the gap at West- 

 wood. The consideration of the approximate and comparative age of 

 some of these coals, with reference to the pi-oductive coals toward the 

 western end of the field, will be continued in connection with the dis- 

 cussion of the fossil plants of the various horizons. Plant collections 

 have l)een made from eleven different horizons, marked A-N in the 

 section, as well as from the roof of the Twin coal, marked O. 



Other published sections excellently illustrating the lithology of the 

 Pottsville formation in the Southern Anthracite field are those at 

 Hacklebarney,^ Nescjuehoning Gap,- and Locust Gap at Tamacjua,^ 

 in the region east of Pottsville. The character of the sedimentation 

 in the region north of Pottsville is shown by the records of the 

 diamond-drill bore holes near the Altamont colleries, throughout a dis- 

 tance of 5 or t> miles along Proad Mountain.* 'Phc composition of the 



1 Atlas Southern Anthracite Field, Pt. I, mine sheet i, cross-section sheet i, columnar-section sheet i, 

 section 4. 



2 Idem, Pt. I, mine sheet ii, colummir-section sheet ii, cross-section sheet ii. 



3 Idem, Pt. I, mine sheets iii and iv, columnar-section sheet ii, cross-section sheet iii, section 39, 

 profile 12. 



*ldem, Pt. IV, columnar-section sheet ix, sections l-(j. 



