WHITE.] AGE OF THE COALS IN LORBERRY GAP. 833 



erii apex of the field, Sharp and Stony mountains become confluent 

 by the convex contents of the ])asin, and from that point westward, as 

 the successive terranes ''spoon out,'' the basin forms a single crest, 

 known as Short Mountain. The topography of the basin is repre- 

 sented on the Pine Grove. Lykens. Hummelstown, and Harrisburg 

 sheets of the Topographic Atlas of the United States. 



The areal geology of the region, as shown in mine sheets xxi-xxvii, 

 inclusive, of Pt. Ill of the Atlas of the Southern Anthracite Field, is 

 essentialh^ correct except as to the mapping of the Pottsville forma- 

 tion, which, as will presently ])e shown, is, together with the Lykens 

 groups, located quite to the north of the Lykens groups as they 

 actually exist in Sharp Mountain throughout the greater part of the 

 length of the basin. Cross sections are shown on sheet xxi. Atlas 

 Southern Anthracite Field, Pt, V; and several columnar sections, based 

 principally on the work of R. C Tajdor and the first survey, are 

 given on columnar-section sheet viii, Pt. IV B. Descriptions, usually 

 of a fragmentary character, and based chiefly on Taylor's ^ reports of 

 the explorations and developments of the field prior to IS-iO, are giA^en 

 by Rogers,' and in more complete form, with additions derived in part 

 f rom Ta^dor's notes, b}- A. DW. Smith, -^ both of whom reproduce in 

 modified form the sections published by Dr. Taylor. 



It is to the southern or Sharp Mountain liml) of the basin that 

 the discussion in this paper will, for the most part, be confined. The 

 key to the stratigraphic problem in hand is the Lorberry Gap section, 

 at the eastern extremity of the basin, and this will first be considered. 



AGE OF THE COALS IN LORBERRY GAP. 



SECTION AT LORBERRY GAP. 



(Station 17, Pi,. CLXXX.) 



On entering upon the study of the plants from the Pottsville forma- 

 tion in the type region, when endeavoring systematically to obtain 

 fossils from the greater number of mines or more important drifts 

 located in diflerent parts of the field, Lorberry Gap, -i miles south of 

 Tremont and about 2 miles south of the Lincoln mine, was selected as 

 a favora))le locality, since in the latest published anthracite mine 

 sheets several of the L3^kens coals are represented as mined there. 

 This point was also thought to be especially important, because it 

 appeared to ort'er good facilities for securing fossils directly from 

 drifts in Lykens coal No. ti, concerning which it is still desirable to 

 obtain more paleontologic data. 



1 Two Reports on the Stony Creek Estate, 1840. See also: Report on the Swatara Mining District. 

 Pennsylvania State legislature, 1839, p. l(i, diagram. 

 2Geol. Pennsylvania, Vol. II, Pt. I, pp. 19:5-198. 

 sSummary Final Report, Vol. Ill, Pt. I, p. 2141. 



20 GEOL, PT 2 53 



