236 DR. THOMAS STERRY HUNT ON THE 
not of primary age.” Subsequently, in the same volume, he noticed the later view of 
Rogers already stated, and apparently accepted it, at least for the ores of Warwick, of Corn- 
wall, and of Chestnut Hill, where magnetite is closely associated, in adjacent strata, with 
limonite. Frazer, however, in 1876, still maintained the early view of Rogers for the ores 
of Dillsburg, in Adams county, which he describes as included in the mesozoic series, * 
and they are so classed in McCreath’s Report M. 3, of the present geological survey, in 1881, 
(preface, page x.) 
§ 48. From my own somewhat extended studies of all the localities known along 
the two borders of the mesozoic belt in Pennyslvania, I am constrained to maintain the 
opinion expressed by me in 1875, that the ore-beds near Dillsburg form no exception, 
but that these, with the deposits of ore at Cornwall, at Wheatland, in the vicinity of Read- 
ing, and at Boyerstown, on the north; as well as those of the Warwick and Jones mines, on 
the south, all belong to the same ancient horizon. That they are met with chiefly along the 
borders of the mesozoic-sandstone belt, as I then said, “is due to the fact that these ancient 
ore-bearing rocks, from their decayed condition, and their inferior hardness, haye been 
removed by denudation, except where protected by the proximity of the newer sandstones, 
or by eruptive rocks, as is the case at the Cornwall mine.” + There, as I have pointed out, 
the dykes from the neighboring mesozoic area have served as barriers, and have preserved 
from erosion a great mass of magnetic iron-ore. 
§ 49. The stratigraphical relations of these ore-bearing rocks serve to show that they 
must be referred to the Primal schists which underlie the mesozoic sandstones. These 
latter, which are generally regarded as of triassic age, form a continuous belt from the 
banks of the Hudson south-westward across New Jersey and Pennsylvania into Virginia. 
Throughout this region, as is well-known, these newer rocks have everywhere a moderate 
and very uniform dip to the northwestward, of from ten to thirty degrees, and were depos- 
ited upon the worn surfaces of the previously folded Primal and Auroral rocks, which 
have contributed largely to the materials of the mesozoic. These older strata, unlike the 
latter, present everywhere considerable undulations, with dips, sometimes at high angles, 
alike to the northwest and the southeast. The unconformably overlying mesozoic zocks, 
now themselves affected by a gentle and pretty uniform inclination to the northwest, 
agree nearly with the older rocks in strike ; and the coincidence which thus appears between 
the mesozoic and the northward-dipping outcrops of the older rocks readily explains how 
the two have been confounded. 
§ 50. In the vicinity of Dillsburg,where numerous openings for iron-ore have been made, 
the dip of the enclosing strata, so far as observed, is to the northwest. The same condition 
is seen at Wheatfield, to the east of Cornwall, where several lenticular masses of magnetite 
have been mined; but at Fritztown, less than half a mile to the southward, the similar 
ore-bearing strata dip to the southeast. Again, at the Roudenbusch mine, near Reading, is 
a bed of magnetite which had, in 1875, been mined for a distance of 480 feet down the 
slope of the bed; the dip being thirty degrees in a direction S. 80° E. At the Island mine, 
also near Reading, is a similar opening for ore, which had been followed 240 feet on the 
incline, with adip of forty-five degrees to the southeast ; while immediately to the north of 


* Second Geological Survey of Penn. Report C. page 71; and Ptoc. Inst. Mining Engineers, v. 133. 
{ Proc. Inst. Mining Engineers, iv. 320. 

