574 



SCIENCE 



[N. S. Vol. XXVIII. No. 721 



tliickness of over 20,000 feet. In the upper part 

 there is a large trap sheet, about 1,500 feet thick, 

 which shows the character of an intrusive sill. 



Copper was first mined in this region at Bow- 

 man Hill, on the Delaware, by the Dutch, from 

 New Amsterdam, about 1650. But the most im- 

 portant early operation was the Old Perkiomen 

 Mine, at Schwenksville, opened about 1700. 



Three types of deposit are known: those con- 

 nected VFith trap sills, those in fissure veins and 

 those in unaltered shales. Deposits of the first 

 type show grains and streaks of bornite and 

 ehalcopyrite scattered through the metamorphosed 

 shales. In the second 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 chrysoealla occasionally found in 

 the undisturbed and unaltered sedimentary rocks 

 is obscure. Though perhaps none of these deposits 

 is sufficiently rich to repay working, they are not 

 without their interesting features. 

 Petrography of the Newark Intrusive Diabase of 

 'New Jersey : J. Volnby Lewis, Rutgers College. 

 The intrusive trap that forms the Palisades of 

 the Hudson extends in outcrops several hundred 

 feet thick from west of Haverstraw, N. Y., south- 

 ward to Staten Island and, somewhat intermit- 

 tently, westward across New Jersey to the Dela- 

 ware River, having an aggregate length of out- 

 crop of about 100 miles.^ It is everywhere a 

 medium to fine-grained dark gray heavy rook, 

 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 some- 

 times 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 con- 

 stitute 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 



' J. Volney Lewis, " Structure and Correlation 

 of the Newark Trap Rocks of New Jersey," Bull. 

 Geol. Soc. of America, Vol. 18, 66, 195-210; also 

 " Origin and Relations of the Newark Rocks," 

 Ann. Rept. State Geologist of New Jersey, for 

 1906, pp. 97-129. 



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 mag- 

 nesia vary inversely. The augite is rich in these 

 latter constituents and poor in alumina, giving a 

 great preponderance of the hypersthene and diop- 

 side molecules. The feldspars range from ortho- 

 clase 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 pro- 

 portions of the minerals, augite usually comprises 

 about 50 per cent, of the rock, the feldspars about 

 40 per cent., quartz 5 per cent, and the ores 5 

 per cent., constituting a quartz-diabase, with 

 normal diabase and olivine-diabase facies. In the 

 quantitative system it is chiefiy a camptonose 

 (III., 5, 3, 4), with the acidic dacose (II., 4, 2, 4) 

 and tonalose (II., 4, 3, 4) and the more basic 

 auvergnose (III., 5, 4, 4, 5) facies. The olivinic 

 ledge is Palisadose (IV., 1^ 1^, 2), the name here 

 suggested for this hitherto unnamed subrang. 



Slight basic concentration at the contacts, pos- 

 sibly according to Soret's principle, followed by 

 differentiation by gravity during crystallization 

 of the main mass, especially by the settling of 

 olivine and the ores and the rising of the lighter 

 feldspars in the earlier and more liquid stages of 

 the magma, accounts for the facies observed and 

 their present relations. 



The Origin of Beach Gusps: D. W. Johnson, 

 Harvard University. 



Two theories have been advanced to account for 

 the origin of beach cusps. According to one the- 

 ory the cusps result from the accumulation of 

 seaweed along the shore and the breaking of water 

 through the seaweed barrier, removing sand and. 

 gravel where the break occurs and molding the 

 remaining deposits into cuspate forms. According 

 to the second theory the cusps are formed where 

 intersecting waves reach the shore. There are 

 serious theoretical objections to both these the- 

 ories and still more serious practical objections. 

 Experiments show that the cusps can be formed in 

 the laboratory by parallel waves which are in 

 turn parallel to the beach ; and numerous observa- 

 tions seem to show that they are generally so 

 formed in nature. The cause of cusp formation is 

 to be found in the physical properties of fluids 

 descending an inclined plane, as will be shown 

 more fully in a forthcoming paper. 

 The Form of Nantasket Beach: Wm. G. Reed, Jr., 

 Harvard University. 

 Nantasket Beach consists of several drumlins 



