858 FLOKAL ZONES OF THE TOTTSVILLE FORMATION. 



transition, 400 or 500 feet in thickness, such us is exhi])ited in the sec- 

 tions at the Pottsville Gap, Pis. CLXXXI, CLXXXII, and in the 

 Lincoln region. Pis. CLXXXII, CLXXXIII. It is purposed in the 

 following pages to present the results obtained by both methods. 



Begiiuiing with Mauch Chunk, at the eastern apex of the Southern 

 field, and proceeding westward, the measurements of the Pottsville 

 formation (XII), as given l)y Rogers,^ are: Mauch Chunk, about 950 

 feet; Nesquehoning, 792 feet; Tamaqua, about 803 feet; Pottsville, aljout 

 1,030 feet; Lorberry Gap, about 675 feet;^ Yellow Springs, about 660 

 feet;^ Kohlers Gap, 230 feet; Bear Gap, 460 feet. The measurements 

 of all the intervals given by A. DW. Smith are of great value, since 

 his statements are based on the enormous amount of instrumentally 

 accurate data accunudated by the second geological survey of the 

 anthracite regions, all of which were passed in review b}- him. As 

 stated b}^ Mr. Smith, in the Final Summary Report, the thickness of 

 the formation is as follows: Locust Gap, Tamaqua, 1,296 feet; Sharp 

 Mountain Gap, Tamaqua, 1,130 feet; Broad Mountain, about 1,200 

 feet; Pottsville Gap, 1,350 feet; Swatara and Rausch gaps, 1,100 or 

 1,200 feet; Lorberry Gap, 1,500 or 1,600 feet;' vicinity of the Lin- 

 coln mine, 1,475 feet; Kalmia region, 1,400 to 1,500 feet; Williams- 

 town, about 1,400 feet. 



The preceding measurements begin with an ar])itrary Ijoundary, 

 usually Avithin or below the transition series. The following measure- 

 ments start from the topmost bed of red shale and extend to the 

 supposed horizon of the Buck Mountain coal, except along Locust 

 ^Mountain, in the Panther Creek Basin, where the measurements 

 from both the A and B beds are given, it being nevertheless under- 

 stood that the A coal at Tamaqua is referable to the Lower Coal Meas- 

 ures.-^ The measurements opposite the names of localities marked l)y 

 an asterisk (*) are compiled from the sections pul)lished by the State 

 geological surve}-. 



even when a complete section is at hand, to decide where the line between the two formations 

 should be drawn. It is not wife to always take the highest red shale bed as a Hiiiit, as Ix'ds of red 

 shale, usually thin, but in appearance like the mass of No. XI, are not infrequently seen high up in 

 the conglomerates of XII, and occasionally among the overlying Coal Measures; nor will it suffice to 

 take the lowest conglomerate, as beds of conglomerate are often found well down in the red shales 

 of XI. The fixing of a precise limit between the two formations becomes, in many instances, a mat- 

 ter of individual i>reference and judgment." 



' 'ieol. Pennsylvania, Vol. II, Pt. I, pp. 14C and 147. 



•-This, as we have already seen, consists in part, if not wholly, of the beds of tlio Productive Coal 

 Mea.surcs. 



3It is difficult to account for this measurement by Rogers at Yellow Springs, except on the supposi- 

 ti(m that the dense, ferruginous surface deposits which occur in the lower end of the gap were mis- 

 taken by him as indicating the presence of the Mauch Chunk red shale. 



<Theterranes included in this measurement belong for the most i)art, it not exclusively, to the 

 Productive Coal Measures. 



5The Buck Mountain coal, or its supposed horizon, is taken as the upper limit in my measurements, 

 both for the sake of the ini i form it y desired in tlie comparisons and Itecause the true paleontologic 

 base of the formation can not in many cases be (ixed, because of the hick of collections of fossils from 

 a nimiber of horizons not far below the Buck .Mountain level. The paleontologic upper limit of the 

 Pottsville is probably within JOO feet, at most, of the conventional limit, the Buck Mountain bed, in 

 all .sections. 



