576 A. W. GRABAU TYPES OF SEDIMENTARY OVERLAP 



3,000 feet, and is mostly Cambric in age, though the upper beds carry 

 an undoubted Beekmantown fauna. No Middle Cambric fossils have 

 been recognized in this limestone, but an Upper Cambric fauna occupies 

 at least the upper third, exclusive of the portion referable to the Beek- 

 mantown. In Pennsylvania a basal Cambric sandstone has been ob- 

 served in a number of localities resting upon the pre-Cambrics. In the 

 Cumberland valley this bed, known as the Eeading quartzite, is probably 

 near the horizon of the Hardyston quartzite, while the Cumberland lime- 

 stone is in general the equivalent of the Kittatinny. The latter is sepa- 

 rated, in New Jersey, by an erosion interval from the Trenton which 

 follows it; its upper limit is therefore not of the same horizon every- 

 where. Whether or not the same is true of the Cumberland has not 

 been ascertained. The basal sandstone is well shown at the Chickies 

 (Chiques) rock on the Susquehanna above Columbia (Lancaster county), 

 from which locality it takes its name. From the occurrence in it of 

 Scolithes it was formerly referred to the Potsdam by Lesley.* At Emigs- 

 ville a typical Olenellus was found in the sandstone. f Its thickness is 

 estimated at 1,300 feet, though this may be excessive.^ It is succeeded 

 by 1,500 feet of limestones, the upper portion of which carry Ordovicic 

 fossils. 



At Balcony Falls, Virginia, 300 feet of sandstones and slates, with a 

 basal conglomerate bed, form the basal Cambric series (Chilhowee), 

 throughout most of which fossils of the Olenellus series occur. At 

 Monterey and along the Blue Eidge mountains over 4,000 feet of quartz- 

 ites, sandstones, shales, and mottled limestones occur, containing the 

 Olenellus fauna. These are overlain by the Shenandoah limestone, the 

 lower part of which is Middle and Upper Cambric. At Harpers Ferry 

 the Chilhowee series is subdivided as follows :§ 



Feet 

 Shenandoah limestone. 



Chilhowee series: 



Antietam sandstone 500 



Harpers shale 800 to 1,200 



Weverton sandstone 100 to 900 



Loudon formation — slates, sandstones, conglomerates, and lime- 

 stone — maximum 800 



Unconformity. 



Catoctin schist (Algonkian). 



Total Chilhowee 3,400 



* Lesley : Second Geological Survey of Pennsylvania, vol. x, 1885, pp. 16-17. 



t Walcott : Loc. cit. 



$ Bascom : Bull. Geol. Soc. Am., vol. 16, p. 298. 



I Harpers Ferry folio. 



