HAWKINS, LOCKATONG FORMATION OF THE TRIASSIG 169 



Dr. E. T. Wherr}'.^'^ With the tourmaline, in some stage of its formation, 

 ilmenite crystals were produced, some of which are inside the tourmaline, 

 but most of them in shallow pits on its outer surface. There is good rea- 

 son for thinking that the diahase sill at Bvram w^as produced by the same 

 igneous outburst wliich gave rise to the Palisade sill and its supposed ex- 

 tension, the diabase at Xew Hope. The Byram and Xew Hope ilmenites, 

 and also those at Princeton, are probably very nearly or quite contempora- 

 neous. At the time of the expulsion of the titanium from the trap, the 

 tension joints were formed by horizontal heave, as is shown by the By- 

 ram deposit in one of them. The trap also was affected by this move- 

 ment, and joints in the same direction were strongly developed on its 

 margins, but as the central part of the mass was perhaps still fluid, it 

 did not develop the same joint system, but curving joints appeared later, 

 which show only in a general way a tendency to take the same direction. 

 Several fault planes of similar nature in the Pennsylvania Triassic are 

 filled by diabase dikes, which shows that some fluid diabase was probably 

 present at that period. The ilmenite, analcite, etc., in these joints were 

 hence undoubtedly derived from the trap rocks in their cooling stages. 



This system of joints is notably parallel to the Flemington-Hopewell 

 fault series. It is not, however, strictly of the same age, since the move- 

 ment of the above named faults has been strongly vertical, without any 

 kno^^^l horizontal component. Such a fault as the Flemington-Hopewell 

 one, with a throw of 17,000 feet, indicates a disturbance of large dimen- 

 sions in the basement rocks below. The resulting strain effects upon the 

 Triassic must have been widespread and thoroughly distributed. This 

 faulting did not, of course, take place all at one time. The great Flem- 

 ington fault has probably been of very gradual production. Movement 

 along this line is evidently still taking place, as shown by the not infre- 

 quent earthquakes experienced in Doylestown. Probably the first indica- 

 tion of this movement was a little sagging under the center of the basin, 

 accompanied by the formation of a slight s}Ticline in the later rocks 

 above. In the formation of this svncline, the lower layers of the Triassic 

 were stretched. The most brittle layers, among which were the Lockatong 

 beds, gave way first, and tension joints were formed. As the disturbance 

 increased, the movement was changed, wholly to vertical, taking place 

 along a few major lines of fracture, represented by the Flemington and 

 Hopewell faults. The almost total freedom of the Lockatong formation 

 in Pennsylvania from vertical faults of any considerable magnitude is 



2* "Contributions to the miner. Newark group of Pennsylvania." Trans. Wag. Free 

 nst. Sci. of Philadelphia. Vol. VII, Feb., 1910. 



