

walcott.] PENNSYLVANIA. 129 



Ili noting the discovery of the Martic anticlinal in Lancaster County, 

 Dr. Frazer calls attention to its exposing fundamental gneiss and gran- 

 atoid beds in the new railroad cuttings along the left bank of the Sus- 

 quehanna River and how it sheds off to the north and to the south at 

 least 16,000 feet of Primal (Cambrian !) slates. 1 In a special report 

 upon the geology of Lancaster County the same writer describes the 

 character and mode of occurrence of the " Chikis n quartzite. The 

 actual thickness of the quartzite above water level is not much over 

 300 feet. 2 Between the limestones and the quartzite there is, he says — 



A vast series of hydro-mica schists and decomposed argillaceous slates, which in- 

 sensibly grow in the deep more and more chloritic until this mineral lends its color 

 as well as its name to the larger part of the whole formation, but generally the 

 chloritic series is divided from these nacrites by a quartzite. 3 



He says further : 



A vast series of slates intervene between the lowest rocks of all on the Susque- 

 hanna and the formation last described. 4 



As the result of his survey of the southern parts of Montgomery, 

 Bucks, and Philadelphia Counties, Mr. Chas. E. Hall 5 decides that the 

 South Valley Hill hydromica and chlorite slates, which were consid- 

 ered by Prof. Rogers as equivalent to his Primal of the North Valley 

 Hill, are not altered Primal slates, but no other than a series of slates 

 overlying the limestones of No. II or the slates of the Hudson Period. 

 He also gives a description of the Primal quartzite of Rogers, speaking 

 of it as the Potsdam sandstone. 6 He gives his opinion of the age of 

 the sandstone known as the Edge Hill Rock, in Chester County, as 

 follows: "The Itacolumite, or Edge Hill Rock, I consider proven, be- 

 yond dispute, to be the equivalent of the Potsdam sandstone." 7 



In a memoir upon the geology of the southeastern portion of Penn- 

 sylvania, Dr. Persifor Frazer gives a summary of the general charac- 

 ters and geographical distribution of the Primal quartzite and the sub- 

 jacent and superjacent schists. The upper division of the Primal of 

 Rogers is referred to No. Ill or Auroral, and the chloritic schists, sub- 

 jacent to the quartzite, are referred to the Hurouian, the quartzite alone 

 representing the Primal or Potsdam of Rogers. 8 The geographic dis- 

 tribution of the formation in Chester, Lancaster, York, and Adams 

 Counties is represented on the map accompanying the memoir. 



Prof. Lesley, in his description of the geology of Chester County, 

 after the surveys of Messrs. Rogers, Frazer, and Hall 9 writes : 



1 [Note on the Martic anticlinal and on ripple marks on a slab of limestone]. Am. Phil. Soc, Proc, 

 vol. 17, 1878, p. 725. 



2 The geology of Lancaster County. Second Geol. Survey Penn., Rep. Prog, in 1877, CCC. Harris- 

 burg, 1880, p. 7. 



3 Op. cit., p. 5. 4 Op. cit , p. 8. 



6 The geology of Philadelphia County and of the southern parts of Montgomery and Bucks. Second 

 Geol. Survey Pa., C6., 1881, pp. xvii-xviii, 93. 

 6 Op. cit., pp. 7, 8. 7 Op. cit., p. xvii. 



8 Memoire sur la Geologie de la partie sud-e&t de la Pennsylvanie. Lille, 1882, p. 75. 



9 The geology of Chester County, after the surveys of Rogers, Krazer, and Uall. Second Geol. Sur. 

 P6nn.,CCCC; 1883, p.viii. 



Bull. 81 9 



