1913.] NATURAL SCIENCES OF PHILADELPHIA. 117 



in the valley of West Swamp Creek, southeast from Bechtelsville, 

 metamorphosed shales — "baked shales which may belong to the 

 Mesozoic" — overlie blue Paleozoic hmestones. The exposure is 

 not a good one, yet there can be no doubt that actual overlap 

 occurs. 



Additional evidence for this vicinity is furnished by a well record 

 described by DTnvilliers^ as follows: "From the Montgomery 

 county line, at A. Schultz's house, [three miles northeast of Bech- 

 telsville] .... to the north border of the Mesozoic, is a distance 

 of 6,400 feet; the average dip, 30°; calculated thickness of Mesozoic 

 at Schultz's, 3,000 feet; nevertheless, Mr. Schultz's water well 

 struck the limestone floor beneath the Mesozoic at less than 200 

 feet." The supposed outlying patch of limestone, "left bare by the 

 denudation of the thin covering of red shale" (ibid., p. 205) appears, 

 however, to be a calcareous conglomerate bed in the Triassic itself. 



In the extensive Boj^ertown iron mines the limestones bearing the 

 ore were everywhere found to underlie the Triassic beds.^ 



Continuing southwestward twelve miles, there is again evidence of 

 the existence of a local fault, as pointed out by the writer elsewhere,^- 

 but in a trolley cut about a mile from the Schuylkill River an appar- 

 ent overlap is poorly exposed, and then at the Big Dam, northwest 

 of Neversink Station, is the erosion contact described by Rogers.^ 

 Here a fissure in the limestone into which pebbles of the conglomer- 

 ate had been washed was formerly exposed. At present the quarry 

 shows conglomerate composed of but slightly rounded limestone 

 pebbles cemented together by a minimum quantity of red mud 

 resting on a somewhat brecciated limestone, into the cracks of which 

 more or less red mud has percolated, so that it requires very close 

 examination to make out the real contact. In the old iron mine 

 on Fritz's Island, around the bend in the river, and at the Wheat- 

 field mine, seven miles to the west, ore-bearing limestone and sand- 

 stone were found l^eneath the Triassic beds as at Boyertown.i° 



At the great Cornwall iron mine, in Lebanon County, twenty 

 miles further west, Triassic conglomerate overlies, on the south 



® Geology of the South Mountain Belt of Berks County, Second Penna. Geol. 

 Surv. RepL D3, II, pt. 1, p. 200, 1883. 



'Spencer, op. cit., pp. 43-60. 



^ Contributions to the Mineralogy of the Newark Group in Pennsylyania, 

 Trans. Wagner Free Inst. Science, Phila., VII, pp. 1-23, 1910. 



3 Geology of Pennsylvania., II, p. 681, and fig. 568, 1858. 



loD'Inyilhers, op. cit., pp. 336, 337, and 346. 



