288 THE CAMBRIAN. Ibull.8L 



DELAWARE. 



The outcrop of the sandstone referred to the " Potsdam n in north- 

 western Delaware is very limited, and is noted only to indicate its 

 occurrence within the limits of the State. 1 



PENNSYLVANIA. 



The rocks referred to the Cambrian System in Pennsylvania by the 

 latest authorities include the Primal quartzite of Prof. Rogers ; and 

 Prof. Lesley is inclined to consider the sandstone and slate of the South 

 Mountain proper as of Cambrian age. The line of outcrop of the 

 quartzite extends along the boundaries of the various Archean areas 

 from the Delaware River on the northeast, in Bucks, Lehigh, and 

 Northampton Counties, southwesterly, with more or less interruption, 

 across Berks, Montgomery, Chester, Lancaster, York, and Adams 

 Counties, to the Maryland line. Prof. J. P. Lesley's summary is as fol- 

 lows: 



The lowest Paleozoic formation in Pennsylvania, No. 1, logically identified with the 

 Potsdam sandstone of northern New York, makes its appearance along the edges of 

 the limestone No. 2 at the north foot of the Azoic Mountain Range between Bethlehem 

 and Reading in Lehigh and Berks Counties; in Mulbaugh Hill, on the Lebanon 

 County line; in Chicques ["Chickis" of Frazer] Ridge, on the Susquehanna, above 

 Columbia; in the Welsh Mountain in northern Chester, and in the North Valley Hill, 

 which stretches for 60 miles from the heart of Lancaster to the Bucks-Montgomery 

 county lino north of the city of Philadelphia. Its only fossil as yet discovered is a 

 Scolithus, but its position next beneath the Calciferous limestone is too well marked 

 to admit of doubt. Formerly it entirely covered the mountain districts north and 

 south of the Schuylkill River, because it still spreads in sheets upon their sides, and 

 in many places makes their summits, lying unconfonnably upon the gneiss. 



The South Mountains proper, which separate Cumberland from York and Frank- 

 lin from Adams County, do not thus exhibit the fundamental gneiss covered by 

 a coating of Potsdam, but are composed of peculiar sandstone and slate strata sev- 

 eral thousand feet thick, which occupy the place of the Potsdam in the series, but can 

 not certainly be identified with it. They may be considered the equivalents of the 

 Ocoee and Sewanee strata of east Tennessee. * * * We may consider our South 

 Mouutain rocks, therefore, those lying north of the turnpike fault, as of Cambrian 

 age. 2 



The sandstone referred to the Potsdam in Lehigh and Northampton 

 Couuties is described by Mr. Frederick Prime, jr., as "a hard, compact 

 quartzite, of a yellowish color where weathered, and when freshly quar- 

 ried of a grayish tint. • • • The thickness, where it could be meas- 

 ured, was 21 feet. 3 " 



The quartzite varies in thickness Trom 20 to 300 feet, the greater 

 thickness being in the "Chickis" section of Lancaster County, where, 

 according to Dr. Persifor Frazer, it reaches 300 feet. {Southwest of the 



1 Cheater, Frederick D. : Preliminary notes on the geology of Delaware — Laurentian, Paleozoic, and 

 Cretaceous areas. Phil. Acad. Sci. Proo., vol. 36, for 1884, pp. 237-259. 



* A geological hand atlaa of the sixty-seven counties of Pennsylvania, embodying the results of the 

 field work of the survey from 1874 to 1884. Second Geol.Surv. Pa.,X, 1885, pp. rvi, xvii. 



3 Geology of Lehigh and Northampton Counties. Second GeoL Snrv. Pa., D 3 , voL 1, 1883, p. 205. 



