ott.J PENNSYLVANIA. 125 



In the fourth report 1 formation No. 1 is spoken of as the extensive 

 slate and sandstone formation constituting a The lowest member of our 

 older Secondary or Appalachian rocks." The slates of the Pigeon 

 Hills are referred to the lowest Secondary formation of the State, and 

 the strata comprise different portions of formation No. I, consisting of 

 dark slate and a light colored sandstone. The stratigraphic succession 

 of the various beds referred to formation No. I of South Mountain, south- 

 west of the Susquehanna, is given in detail. The intercalated limestone 

 bed is considered to belong to the upper part of the division, 2 and there 

 is a bluish slate interstratified in the sandstone. In the report of the 

 following year 3 the geographical range of the rocks of the South Moun- 

 tains from the Delaware to the Schuylkill is outlined. The white and 

 gray sandstone of formation I is not a continuous stratum in the belt 

 of the South Mountains where they traverse Northampton and Lehigh 

 Counties, but it is very probable it occurs at the base of all the primary 

 ridges, buried under a deep covering of loose diluvium. 4 Mention is 

 made of its various points of outcrop and its occurrence in Berks 

 County, and many details are given of the distribution of the sand- 

 stone and the mode of its occurrence in relation to the subjacent pri- 

 mary rocks. 



In his grand summary of the geology of Pennsylvania, Prof. H. D. 

 Rogers gives a synoptic description of the Primal series or " Potsdam n 

 Bauds' tone of New York, as follows : 5 



The Primal series, under its fullest and most di versified condition, or that which it 

 wears m the Appalachian chain in Pennsylvania, Virginia, and Tennessee, is a thick 

 fourfold group composed of two slates and two great arenaceous rocks in alternation: 

 (1) The highest or Primal newer slate is a greenish and brownish talco-argillaceous 

 slate, sometimes very soft and shaly. Iu Pennsylvania it has a thickness of about 

 700 feet. (2) The next, the Primal white sandstone, is a compact, white and yellowish, 

 tine-grained, vitreous sandstone, often containing specks-of kaolin. This rock, which 

 . is of easy recognition and of an immense range, has a thickness iu some parts of the 

 Blue Ridge of Virginia of at least 300 feet. This is the Potsdam sandstone of New 

 York. (3) The Primal older slate is a brown and greenish gray sandy slate, contain- 

 ing much feldspathic and talcose matter. It has hitherto disclosed no fossils. The 

 thickness of this bed in the Atlantic slope in Pennsylvania is several hundred feet, 

 and iu the Blue Ridge of .Virginia is not less than 1,200 feet. (4) The Primal con- 

 glomerate, the lowest of the yet distinctly recognized formations of the Primal series, 

 is a heterogeneous conglomerate of quartzose, feldspathic, and slaty pebbles, imbed- 

 ded in a talco-silicidus cement. The thickness of this rock in Virginia and Tennes- 

 see, north of which it has not been discovered, is at least 150 feet. 



In New York and the Northwestern States this series presents a materially different 

 type, the Primal white sandstone being almost the sole representative. 



Thickness. — The thickness of the entire series is considerably more than 2,000 feet. 



1 Rogers, H. D. Fourth Annual Report on the Geological Survey of the State of Pennsylvania. 

 Harrisbnrg, 1840, pp. 33-35. 



2 Op. cit.,p.41. 



3 Rogers, H. D. Fifth Annual Report on the Geological Exploration of Pennsylvania. Harrisburg, 

 1841, pp. 16-26. 



4 Op. c,it.,pp.26,27. 



* The Geology of Pennsylvania. Philadelphia. 1858, vol. 2, pp. 751, 752. 



