JVALC0TT.1 SUMMARY MARYLAND. 289 



Susquehanna River it is difficult to measure its exact thickness, owing 

 to its disturbed condition. The characters of the sandstone appear to 

 be very much alike throughout the State, and the only traces of organic 

 remains found are the straight, vertical tubes of Scolithus. 



Prof. H. D. Rogers referred a series of slates, between the sandstone, 

 called Potsdam, and the base of the superjacent limestoue to the Primal 

 period, but the geologists of the Second Geological Survey consider them 

 as belonging to the limestone series. If a comparison be made with the 

 Tennessee sections, where the schists and shales between the quartzite 

 and the limestone are characterized by Cambrian fossils, this series of 

 schists will certainly be referred to the Cambrian, as it is subjacent to 

 the great limestone series and superjacent to the quartzite*. According 

 to Prof. Rogers, the highest or Primal newer slate is a greenish and 

 bluish talcose argillaceous slate, sometimes very soft and shaly, and 

 has a thickness of about 700 feet. Dr. Frazer refers about 1,600 feet of 

 " Hydromica schist "" to the interval between the quartzite and lime- 

 stone in York County. 1 



The upper part of the Primal slates does not appear to be developed to 

 the northeastward in Lehigh, Northampton, Bucks, Montgomery, Berks, 

 and Chester Counties. It first appears with any consi derable thickness 

 in Lancaster County, near the Susquehanna River, and south of the 

 quartzites of the Chickis Hills. From thence it extends southwesterly, 

 across York and Adams Counties, to the Maryland line, increasing in 

 thickness in Maryland and Virginia. 



Asa whole, the Cambrian System in Pennsylvania appears to be rep- 

 resented by the lower quartzite and the superjacent shales and schists 

 as originally defined by Prof. Rogers, and it may be that the lower 

 portion of the superjacent limestone will be included. 



In a letter received from Prof. Lesley, dated May 8, 1890, he says: 



Reading Ells's paper and Brainerd & Seely's paper in Bull. Geol. Soc. America, just 

 published, with your remarks at the meeting, I naturally reverted to my South Moun- 

 tain surveys (20 years ago) east of Chambersburgh, Pennsylvania (Fulton and Adams 

 counties), and the strange and powerful impression made on me then by the outcrop 

 of a low ridge of purple shales, running from the pike southward, just hack (east) of the 

 western mountain ridge. I never saw anything like them, and feel strongly in- 

 clined to consider them the Sillery purple shales (Cambrian) of the North. I can't 

 find or remember any description of this outcrop by Frazer. It lies in Fulton County, 

 outside the Adams County line. 



MARYLAND. 



I have been unable to find any detailed account of the rocks referred 

 to the Primal series of Prof. Rogers, and have depended upon the gen- 

 eral account given by Prof. P. T. Tyson in 1860, in his report as State 

 agricultural chemist. His description is short and will be quoted in 

 full: 



(Primal of Pennsylvania survey .) — Potsdam of New York. — This division includes: 

 (1) A hard sandstone made up of grains of quartz, with occasionally grains of 



'General notes.— Sketch on the geology of York County, Pennsylvania. Am. Phil. Soc. Proc, vol 

 23, 1886, p. 401. 



Bull. 81 19 



