130 J. F. Kemp — Porphyrite Bosses in New Jersey. 



Art. XYIL — On Certain Porphyrite Bosses in Northwestern 

 New Jersey • by J. F. Kemp. 



Across the northwestern portion of New Jersey the Hudson 

 River shales extend in a broad band some six miles or more in 

 width.* The general trend of the outcrop is northeast. To the 

 northwest they run under the Oneida conglomerate forming 

 Kittatinny range, and on the southeast are themselves under- 

 laid by limestone of earlier age. West of Deckertown the 

 shales have been the scene of extensive eruptive phenomena. 

 Between them and the Oneida conglomerate the great elaeo- 

 lite-syenite dikef described by Professor B. K. Emerson;}; comes 

 out, causing extensive contact metamorphism, and a mile or less 

 east of this dike and wholly in the slates are to be seen the 

 curious bosses or hillocks of eruptive rock referred to in the 

 New Jersey Report for 1882, p. 67. Also, some ten miles 

 southeast, at Franklin Furnace, we find the bed of franklinite 

 intersected by the several dikes of mica-diabase described by 

 Professor Emerson,§ and other evidences of eruptive rocks 

 were found by Dr. N. L. Britton northwest of Franklin 

 Furnace. I From these citations it will be seen that records 

 of eruptive action are numerous in this district over an area 

 ten miles or more in diameter. 



Having been engaged in studying a collection of massive 

 rocks for the N. J. Survey in 1886, the writer felt interested, 

 now that the survey has lapsed, in pursuing the subject further, 

 and was so fortunate, while doing the field work, as to have 

 the aid of Mr. William S. Vanderhuff of Deckertown, whose 

 thorough knowledge of the district it would require long 

 residence to equal. 



The accompanying map illustrates the region and has been 

 imperfectly reproduced from Sheet No. 1, of the State Survey 

 maps and afterward partly filled in with right line work to 

 show the portion formed by the Oneida Conglomerate. The 

 shales strike generally northeast where a strike can be observed, 

 but as the eruptive rocks are neared it is difficult to satisfy 

 oneself as to their bedding, for it has been largely destroyed by 

 the baking influences to which the shales have been subjected. 



There are in all some eight exposures. These are distributed 

 in an irregular north and south direction as indicated by heavy 

 lining on the map. The largest is in B2, the other seven in 

 A5, B5 and B6. The great dike of Professor Emerson runs 



*Cf. Geol. of K J., Map, 1881. fGeol. Surv. of N. J., p. 144, 1868. 



% This Journal, III, xxiii, p. 302. § Ibid., p. 376. 



|| Geol. Surv. of N. J., p. 110, 1886. 



