458 



Report of the State Geologist. 



The hornblende is brown and in irregular masses, with magnetite and apatite 

 inclusions. It is often bleached to a green variety. The augite contains the 

 same inclusions as the hornblende. The feldspar is well twinned, and 

 inclusions of magnetite and apatite are not uncommon. 



Another camptonite dike has been described by Professor Kemp from 

 the Forest-of-Dean mine. The dike is about six feet wide and cuts across the 



ore-body at an acute angle. It consists of plagioclase, hornblende and 

 magnetite, with alterations of the first two. Secondary magnetite also occurs. 

 An analysis gave : 



Si 2 48.19 



AL, 3 16.79 



Fe 2 3 18.37 



Ca O 6.85 



Mg 1.32 



K 2 l.n 



Na 8 O 5.59 



Loss on ignition 2.31 



100.53 



These two dikes are the only ones from the Orange county Highlands 

 which have been described in detail. 



The writer, during his field work this summer, found several other 

 camptonite dikes in this region, which are very similar to each other and to 

 those described by Professor Kemp. 



( >ne <>f these is at the turn of the road, south of the Forest-of-Dean mine, 

 near the east end of the reservoir pond. The dike is six feet wide and extends 

 east and west through the biotite gneiss. The latter strikes N. 10° E., and 

 dips 50° E. The dike rock is light grey and has minute acicular hornblende 

 crystals which are visible in hand specimens. Sections of the dike show it to 

 consist of hornblende on plagioclase, both much decomposed. The horn- 

 blende needles and shreds lie with their longer axes parallel. Another dike 

 cuts the gneiss at the west end of the pond. It is almost under the bridge 

 crossing the creek at this point. This, however, is an olivine-augite camptonite. 

 The section of this rock shows granular pyroxene, lath-shaped plagioclase and 

 magnetite grains in the ground-mass, with phenocrysts of olivine. There is 

 also some glassy material in the ground-mass. The olivine is altered to 

 serpentine along the cracks and around the edges, with the development of 

 curiously shaped magnetite grains. 



