1885.1 [Frazer. 



made up of little glinting particles. In the former case the beds are very 

 often strewn with pyrite. Again, in place of these crystals of iron — and 

 occasionally copper— sulphide, are beautiful casts or moulds of the shape 

 of a cube, more or less filled with a dark brown iron rust obtained from 

 the decomposition of the original crystals. These little crystals have 

 been of no small importance to the prosperity of York county, for there is 

 good reason for believing that by far the largest part of its iron ores have 

 been derived from their oxidation, transportation by water and final 

 deposition in the clays formed from the grinding up of the rocks which 

 originally contained them.* 



These argillites, or limestone schists, as I have sometimes called them, 

 in all probability hold all the important iron oref mines of the county, 

 outside of the formation of red sandstone and shales. It is true that 

 sometimes the iron ore banks appear to be far from the area colored as 

 limestone, and sometimes directly within the boundaries of that area, 

 but in neither case is it under conditions that forbid the belief that they 

 are in the veritable hydro-mica schists, even if the latter may have been 

 reduced by the weather to soft unctuous and variegated clays. It is not 

 assuming too much, therefore, to call this portion of York county rocks 

 the real iron-bearing region. The edges of the rock appear in the right 

 bank of the Susquehanna river, where that river has cut through them, and 

 one would select the part just above Wrightsville to ascertain whether 

 these schists were unconformable upon the quartzite ; but the following 

 records of the dip, or inclination of the two rock series taken from section 

 1 of my report on the county,}: will show that both formations are so 

 flexed or twisted, that no certainty can be obtained there. First, there 

 are two dips in the Quartzite of South— 50°, and almost at the contact 

 wi h the schists S. 20°, E. — 45°. Next there are three dips in the schists 

 which are respectively S.— 45°, S. 10°, E.— 50°, S.— 10°, E.— 10°. Still, 

 there is every probability that in fact the dips of the two differ, both in 

 direction and amount, while there are no such indications for the dips of 

 the schists and of the limestone proper at this place. § These schists are 

 colored dark-green in the accompanying map. 



The York Limestone with Argillites. — One of the best opportunities of 

 measuring the thickness of this limestone is afforded by the section 

 referred to along the Susquehanna from a little run half a mile above the 

 Columbia bridge to Creitz's creek. This is evidently a trough with the 

 axis close to the bridge, and measures 2800 feet of limestone and in- 

 cluded schists. If the schists between the quartzite and the limestone 

 be included, it would add some 1600 feet to this, making the limestone 



* See Volume C, p. 137, 2d G. S. of Pa., by the author. 



t See Note 3, at the end. 



% Vol. C, p. 7S. 



gin the section above referred to it is probable that a further study would 

 enable me to abandon the hypothesis of non-conformability at g,i,k and o, 

 which I considered necessary eleven years ago. 



PRQC. AMER. PHILOS. SOC. XXIII. 123. 2y. PRINTED JUNE 11, 188(5. 



