Frazer.] OJO [Dec. 4, 



(as at Glen Rock), which maybe safely assumed to be of earlier date than 

 the important York limestone, whether or not it be (as seems not improba- 

 ble) a part of the regular Huronian series. 



The most extensive iron ore banks noted in or on the border of this in- 

 termediate belt are the Brillhart and Feigley banks marked Nos. 11 and 

 12 on the map. 



The Peach-Bottom district, including the roofing slates lying to the 

 south of the flat arch, was described by me in volume CCC, Second 

 Geological Survey of Pennsylvania, in 1877, where I showed that its posi- 

 tion in the series was doubtful, and that these rocks might be interpreted to 

 represent the Upper Archaean (a 3 ) (below the Potsdam) ; or the schists imme- 

 diately above the Potsdam (sj; or (by supposing a fault), a formation still 

 higher — the "Matinal " of Rogers. Since then fossil algae were furnished 

 to Prof. James Hall from the quarries, but he was unable to determine 

 the age of the rocks from them with greater precision, than to refer them 

 to the second or third of these horizons, with a preference to the second.* 

 Photographs of the quarries and of the manner of working them will be 

 found in volume CCC, Second Geological Survey of Pennsylvania. f 



The Palaeozoic Rocks. 

 Cambric (Hellam Quartzite, Potsdam Sandstone), (cb) 



Prof. H. D. Rogers, in the First Geological Survey of Pennsylvania, 

 marked out and described the members of the different formations repre- 

 sented in the State. This formation, which we may consider the base of 

 the Palaeozoic, was considered by him to consist of three parts : a lower 

 series of "talcose " slates, a middle white sandstone, and an upper series 

 of talcose slates. It will be easily understood, by what has just been said, 

 to what extent the view here offered differs from that of our great pioneer 

 geologist. These "lower talcose slates," in all probability, are identical 

 with the Azoic schists (or phyllites) just described, and, therefore, 

 their position relatively to the beds beneath them and above them is 

 the same, whether they be considered Upper Archaean or Lower Palaeozoic. 

 There are no good exposures of the Hellam quartzite with the slate 

 below it at any place in York county which I recall. On the flank of 

 the South mountain, the quartzite is very much rent and crushed into 

 fragments, while of the small patch on the map about two miles west of 

 Case's ore bank (No. 8 on the map) no accurate dip was recorded. The 

 Hellam quartzite, of which a part composes the "Chikis mountain," 

 exhibits, indeed, in its numerous foldings the rock, called by Rogers, 

 "talcose slate," between its two principal beds of quartzite, but not 

 appreciably lower than the latter. We are forced to look to other parts of 

 the country for a clearer knowledge of the relation to each other of this 

 quartzite, and the schists on which it rests. We find abundant instances 



•See Peach-Bottom slates of S. K. York and S. Lancaster counties, Proc. Am. 

 Inst, of Min. Engrs. Troy meeting, 1883. 

 fSee note No. 2 at the end. 



