HAWKINS, LOCKATONG FORMATION OF TIIF TRIASSIC 171 



prevailing dip of fifteen or twenty degrees would carry the trap a mini- 

 mum distance of 1500 feet above the mineralized zone at Princeton. The 

 most strongly and typically mineralized zone extends at intervals from 

 Princeton to Eushland, Pa., the whole of which area is flanked on the 

 north by an irregular diabase sill whose original extension may have been 

 2000 feet or so above the present exposed Lockatong. At the north end 

 of the formation, the Eocky Hill diabase extends up through it, and being 

 very irregular, may extend under it, or may be connected with a sill which 

 lies under it. The presence of small but persistent dikes to the south 

 attest to the presence there of at least some igneous activity. Brookite is, 

 moreover, seemingly authentically reported from Phoenixville. 



Solutions that originated with the intrusive rocks of the Triassic 

 usually travelled upward rather than downw^ard. This is shown to a great 

 extent in the region just northwest of New Brunswick, N. J., where the 

 shales are filled with frequent small copper deposits that have come up in 

 solution from the diabase below. Such solutions travelled upward be- 

 cause there were more open cracks and fissures above the intrusive than 

 below it. Large fissures such as fault zones, as at Menlo Park, furnished 

 channels along Avhich solutions rose for thousands of feet. Mineralized 

 solutions were, however, abundantly present below the slowly cooling trap, 

 as well as above it.^® Ilmenite crystals have been noted in feldspar seams 

 just below the Palisade sill. In case a well developed series of open 

 cracks existed at the time of intrusion, or such a series were opened by 

 some widespread force acting before the intrusive had fully cooled, such 

 solutions might find their way a long distance downward. Unless such 

 action can be supposed in the vicinity of Princeton, we must look for the 

 origin of these mineral deposits in another intmsive at a lower horizon, 

 which would occupy a position beneath the Lockatong rocks of Princeton 

 and the region south for some distance. The existence of such an intru- 

 sive, while possible, finds no proof in any evidence gathered in the field. 



In some of the exposures, notably at Princeton and at Lawrenceville, 

 vertical joints are coated with a thin film of black bituminous matter. 

 This material resembles anthracite coal or one of the dense asphalts. Its 

 luster is bright and its fracture conchoidal. It has been derived from 

 disseminated organic matter of the black shales, and, circulating as liquid 

 or gaseous hydrocarbons, it has been deposited in the vertical joints, 

 which were the only available openings. Whether its concentration is 

 connected with the injection of the diabase is a question ; but as just such 

 bituminous matter is seen on vertical joints at many points throughout 

 the Newark series, any such connection is improbable. 



2« See reports of the State Geologist of New .Jersey for lOOG and 1007. 



