lo THE AMERICAN MUSEUM JOURNAL 



opportunity for the formation from circulating waters of inter- 

 esting little globules of sphaerosiderite and several members of 

 the group of zeolites, such as heulandite, harmotome, stilbite 

 and chabazite. The stilbite occurs in noteworthy rosettes of 

 slender, blade-like yellowish brown crystals upon the surface of 

 the rock. These zeolites are particularly interesting for study 

 in comparison with the remarkable specimens of the same spe- 

 cies which have come from the cavities in the trap rock (diabase) 

 of the neighboring Palisades. 



The chief cabinet mineral of the hornblende schists is sphene, 

 which occurs in showy groups of yellowish green, flattened crys- 

 tals. The principal constituent of the schists, however, is black 

 hornblende, which occurs in needle-like crystals. Epidote- too 

 and actinolite are often found in this rock. Exposures may be 

 seen in Momingside Park and the Fort Washington Heights 

 section of the city, but most other localities have been covered 

 with buildings or streets. 



The granite and pegmatite veins or dikes are the principal 

 contributors to the local mineral collection. The origin of these 

 rocks is still a mooted point, but probably some of them are acid 

 igneous intrusions, while others, particularly the pegmatites 

 (characterized by their coarseness of crystallization), are the 

 result of chemical precipitation from circulating waters. First 

 to be mentioned are orthoclase, microline, oligoclase and albite 

 among the feldspars ; muscovite and biotite among the micas, and 

 quartz. Garnets of small size are scattered all through the 

 schists, but gigantic crystals of this mineral have been found in 

 the pegmatite veins, the largest of which came from an excava- 

 tion in West 35th Street between Broadway and Seventh Avenue. 

 This garnet is a nearly perfect crystal six inches in diameter and 

 weighs nine pounds ten ounces. 



Black tourmaline is an abundant constituent of the schists, 

 and it occurs in beautiful crystals in the pegmatites. Some- 

 times the minute, flattened crystals imbedded between plates of 

 muscovite have been mistaken for the rare mineral dumortierite. 

 Large crystals too have been found. An imperfect one, twelve 

 inches long and five inches across, is in the Club collection, while 

 a crystal of almost ideal development, about ten inches long and 



