CURRENT PRE-CAMBRIAN LITERATURE 531 
ore deposits occur in white crystalline limestone, which is cut in 
numerous places by dikes of granite, trap, and a rock taken to be 
altered gabbro. The white limestone is closely involved throughout 
its extent with a blue limestone of Cambrian or Cambro-Silurian age. 
Wolff! briefly describes the eruptive rocks of Sussex county, New 
Jersey, with reference to their economic value. ‘These include granite, 
elaeolite-syenite, elaeolite-porphyry, and camptonite, and are treated 
under the head of Archean. 
Westgate’ describes and maps the geology of the northern part of 
Jenny Jump Mountain, in Warren county, N. J. The main ridge of 
the mountain is formed chiefly of gneisses, comprising many varieties. 
These are, from northwest to southeast, and also, according to the 
banding, from base to top (1) granitoid-biotite-hornblende-gneiss, 
containing narrow bands of biotite-hornblende-gneiss ; (2) hornblende- 
pyroxene-gneiss ; (3) biotite-gneiss ; (4) dark biotite-hornblende-gneiss ; 
(5s) granitoid-biotite-hornblende-gneiss ; and (6) dark biotite-horn- 
blende-gneiss, and gray micaceous gneiss. Certain of the dark horn- 
blende-gneisses have been so extensively altered as to be called epidote 
rocks. The gneisses are in general granitoid and massive, and there 
“is a conspicuous absence of schistose rocks and crumpling of the 
banding, the banding over wide areas having uniform strike and dip. 
Along the southeast side of the mountain, at the northeast end of 
the mountain, and in two isolated outcrops within the gneisses of the 
main ridge, are areas of white crystalline limestone. The limestone is 
in all cases closely associated, and perhaps interbanded, with the dark 
biotite-hornblende-gneiss and gray micaceous gneiss (Nos. 4 and 6 
above), and at the northeast end of the mountain also with quartz- 
pyroxene rock. 
Cutting both gneisses and limestone are pegmatite, diabase, and 
amphibolite or granular diorite. 
The origin and age of the gneisses are doubtful. The presence of 
limestone belts closely associated, and perhaps interbanded with the 
‘Report on Archean geology, by J. E. WoLFF: Ann. Rept. Geol. Surv. New 
Jersey, 1896, pp. 91-94. With map. 
2 The geology of the northern part of Jenny Jump Mountain, in Warren county, 
N. J., by Lewis C. WESTGATE: Geol. Surv. of New Jersey, Ann. Rept. for 1895, pp 
21-61, 1896. With geol. map. 
