WHITE] FLORAL ZONES OF THE POTTSVILLE FORMATION. 759 



GEXERAIL, DESCRIPTIOX OF THE SOUTHERX FIELD. 



FORM AND EXTENT OF THE FIELD. 



The Southern Anthracite field, known also as the Schuylkill or 

 Pottsviile, and as the First Anthracite field, is, as its name implies, the 

 most southern of the four fields or regions into which the anthracite 

 basins of Pennsylvania group themselves. It embraces an area of about 

 181 square miles, lying in Carbon, Schuylkill, Lebanon, and Dauphin 

 counties. Its territory is mapped on the Hazleton, Mahanoy, Pottsviile, 

 Catawissa, Shamokin, Lykens, Hummelstown, and Harrisburg sheets 

 of the Topographic Atlas of the United States. Its greatest longi- 

 tudinal extent is a little over 70 miles, from the Lehigh River at 

 Mauch Chunk, in a direction averaging nearly S. 60° W., to within 

 li miles of the Susquehanna Kiver at Dauphin, 8 miles north of Harris- 

 burg. Its maximum breadth is nearly 8 miles, from the crest of Sharp 

 Mountain across Broad ^Mountain, in the region west of Pottsviile. 

 Eastward the field narrows to a width of about 2 miles at Tuscarora, 

 whence it extends, between Sharp Mountain on the south and Locust 

 Mountain on the north, in a linear-lanceolate prolongation, hardly 

 exceeding 2i miles in width, to the Lehigh River. Owing to the 

 structure, the margin on the northwest, in the central portion of the 

 field, is cut in rounded westward-projecting lobes of Broad Mountain, 

 so that at a point a short distance west of Tremont, or about 12 miles 

 west of Pottsviile, the field is reduced to a width of 4 miles. From 

 this point the north and south borders diverge at an angle of about 20°. 

 At the same time a very extensive arch, the Perry Count}" anticline, 

 penetrates the field from the west, causing the parting of the latter, 

 as far as a point about 4 miles west of Tremont, into two narrow 

 divergent arms or prongs, forming what is known as the ''fish tail" 

 of the Southern Anthracite field. The northern of these prongs, the 

 Wiconisco Basin, l3ang between Bear and Big Lick mountains, is 

 about 16 miles long, 2 miles in greatest breadth, and ends in a rather 

 blunt point about 3 miles west of Lykens. The other prong, which 

 also is about 2 miles wide at the base, and which tapers gradually 

 from the latter for 30 miles to near the Susquehanna River, is known 

 as the Dauphin Basin. It is bounded by Sharp. Mountain on the south 

 and by Stony Mountain on the north. 



GENERAL GEOLOGIC STRUCTURE. 



Structurally, the Southern field is a synclinorium — a complicated 

 group of synclines producing a great and, at points, irregular basin. 

 Besides the numerous principal axes of folding, which are conforma- 

 ble with the usual Appalachian trend, there are other oblique, more 

 nearly due east-west undulations, which have had much to do with 



