208 J. V. LEWIS NEWARK TRAP ROCKS OF New JERSEY 



dip steeply downward from its western flank, as Darton supposed, these 

 dikes and sheets would be much nearer it than to any probable feeding 

 fissure for the extrusive sheets. 



In like manner the dike at Bogota, the several dikes east, south, and 

 west of New Brunswick, and those scattered over the region northwest of 

 Sourland mountain are all most readily explained as thin offshoots from 

 the same sill. In fact, some of these north of Sourland mountain have 

 actually been traced by Kiimmel to a direct connection with the great 

 intrusive sheet at the outcrop, and there is little room to question that 

 the others are of the same character. 



The trap of Cushetunh and Round mountains. — These intrusive 

 masses are of the same nature as the great Palisades sill and may be a 

 contemporaneous upward protrusion of the same magma, but this ques- 

 tion can not now be definitely determined. There is an interval of less 

 than dy2 miles between Eound mountain and the dikes about Fleming- 

 ton, which are undoubtedly offshoots of the Sourland Mountain trap. 

 The structure about Cushetunk and Eound mountains is complicated, 

 and outcrops of the shales are too infrequent in the vicinity of the trap 

 masses to permit satisfactory conclusions. Darton* concluded that we 

 have here remnants of a wide intrusive sill "considerably flexed, and with 

 the form of its present outcrops mainly determined by the removal of the 

 trap from the crests of the anticlinals." Kiimmel, f on the other hand, 

 concluded that the curving outline of Cushetunk mountain "is not due, 

 primarily at least, to an anticlinal or synclinal fold in the shales, but to 

 the cxirving fracture through which the trap has come." 



As to Eound mountain, Kiimmel considered it probably intrusive, but 

 did not regard the evidence as definite as in some other cases. Meta- 

 morphic effects recently observed on the slopes of the mountain, however, 

 leave no doubt as to the intrusive character, and this is in harmony with 

 its prevailingly coarse granitic texture. The few observations possible 

 seem to favor Barton's conclusion that Eound mountain "lies in a well 

 defined synclinal, or spoon, and is separated from Cushetunk by a local 

 anticlinal" from which the intervening trap has been removed by erosion. 



In the discussion of the Sand Brook and New Germantown extrusives 

 above it has been shown that a former extension of the Watchung extru- 

 sive sheets over this region may reasonably be supposed. It is further 

 shown below that the intrusives are probably of later date than the 

 extrusives. If these conclusions are correct, it is possible that the up- 

 ward movement of the Cushetunk and Eound Mountain magma was 



* Bull. U. S. Geological Survey, no. 67, p. 64. 



t Annual Report of the State Geologist of Ne^* Jersey for 1897, p. 76. 



