340 J. F. Kemp — Leu cite in Sussex Co., N. J. 



■with some smaller offshoots, but with a strike in the large one 

 of N. 45° W. and a dip of 75° N. The dike had been opened 

 up to a depth of 20 feet or more below the surface and ap- 

 peared quite fresh. Most interesting of all, it was copiously 

 provided with the leucitic spheroids, of which an abundant 

 supply was gathered for investigation. It should be stated 

 that it is the same dike as the one mentioned by F. L. Nason 

 in the Annual Report of the N. J. State Geologist, 1890, 

 p. 35, and determined by Dr. G\ H. Williams as mica-diabase 

 in an altered condition, Dr. Williams evidently recognizing its 

 affinities with the one in the mines at Franklin Furnace. In 

 the fresh condition it is, in the specimens with the spheroids, 

 precisely like the earlier mentioned Hamburg dike. Although 

 this is three miles away, and not exactly in the same line of 

 strike, the two dikes are so near it as to give ground for the 

 suspicion that they are the same rock body. Ten sections were 

 prepared in three of which there appeared some apparently 

 unaltered material in the midst of the analcite and other sec- 

 ondary products. One of these was cleaned of balsam, and 

 on one-half the gelatinizing and staining test was tried. The 

 secondary products gelatinized and stained readily ; the sup- 

 posed fresh material was not affected. On the other portion 

 in small, carefully selected grains, the test for fluo-silicates was 

 tried. Abundant cubes of potassium fluo-silicate* were ob- 

 tained, with but little of the hexagonal sodium salt, much less, 

 in fact of the latter, than the bausch-analysis of the altered 

 spheroids, published in the writer's previous paper (p. 303) 

 would indicate for their general mass. In one of the slides 

 the characteristic twinning of leucite is also developed. 



It would seem therefore to be quite certain that there actu- 

 ally is in Sussex Co., !N\ J., a leucite dike rock, associated with 

 the elaeolite-syenite, and that the determination of a piece of 

 the earlier described dike, by Dr. E. Hussak,f as leucite-teph- 

 rite, although based on altered material and thought by the 

 writer at the time to be premature, really is substantiated by 

 the discovery of satisfactorily fresh material. But it is also 

 quite true that similar spheroids formed entirely of feldspar 

 have developed in the mica-diabase dike at Franklin Furnace, 

 showing thus that instability of the leucite molecule, which 

 has been elsewhere met. 



* These do not appear at once and are only to be obtained by redissolving the 

 first crop in water or dilute HF, and recrystallizing. 



f Neues Jahrbuch, 1892, II. 153. The material was derived from J. F. K. 

 through 0. A. Derby. 



