476 ANNALS NEW YORK ACADEMY OF SCIENCES 



early operation was the Old Perkiomen Mine, at Schwenksville, opened 

 about 1700. 



Three types of deposit are known: those connected with trap sills, those 

 in fissure veins, and those in unaltered shales. Deposits of the first type 

 show grains and streaks of bornite and chalcopyrite, while brecciated fissures 

 are filled with these ores and various accessory minerals. The magmatic 

 origin of the metals in these cases is clear enough, but the source of the 

 films of malachite and chrysocalla occasionally found in the undisturbed 

 and unaltered sedimentary rocks is as yet obscure. Though perhaps none 

 of these deposits is sufficiently rich to repay working, they are not without 

 their interesting features. 



The paper was accompanied by illustrations. 



Professor Lewis said in abstract: The intrusive trap that forms the 

 Palisades of the Hudson extends in outcrops several hundred feet thick 

 from west of Haverstraw, N. Y., southward to Staten Island and, somewhat 

 intermittently, westward across New Jersey to the Delaware River, having 

 an aggregate length of outcrop of about 100 miles. ^ It is everywhere a 

 medium- to fine-grained, dark gray, heavy rock, with dense aphanitic facies. 



The typical coarser rock contains, in the order of abundance, augite, 

 plagioclase feldspars, quartz, orthoclase, magnetite and apatite. The first 

 two occur in ophitic to equant granular textures and the next two in graphic 

 intergrowths which sometimes constitute as much as one-third of the rock. 

 In the contact facies, micropegmatite disappears and scattering crystals 

 of olivine occur. 



A highly olivinic ledge, 10 to 20 feet thick and about 50 feet from the base 

 of the sill, is exposed in the outcrops northward from Jersey City for about 

 20 miles. The olivine crystals, which constitute 15 to 20 per cent, of the 

 rock, occur as poikilitic inclusions in the augite and feldspar. 



Chemically, the trap ranges from less than 50 per cent, to more than 60 

 per cent, of silica, with a corresponding variation in alumina, ferric oxide 

 and the alkalis, while ferrous iron, lime and magnesia vary inversely. The 

 augite is rich in these latter constituents and poor in alumina, giving a great 

 preponderance of the hypersthene and diopside molecules. The feldspars 

 range from orthoclase and albite to basic labradorite. Doubtless there is 

 always more or less anorthoclase, also, since all feldspar analyses show 

 potash. 



While there is considerable range in the proportions of the minerals, 

 augite usually comprises about 50 per cent, of the rock, the feldspars about 



1 J. Volney Lewis, Structure and Correlation of the Newark Trap Rocks of New Jersey, 

 Bull. Geol. Soc. of Amer., Vol. 18, pp. 195-210; also Origin and Relations of the Newark 

 Rocks, Ann. Report State Geologist of N. J. for 1906, pp. 97-129. 



