434 JULIEN 



hattan Island and their association with micaceous gneisses/ 

 Thinly foliated hornblende-schist and gneiss are of common 

 occurrence (Rand, p. 261), and have been thus described by 

 Rogers : ** Metamorphosed with characteristic white streaks of 

 imperfectly developed crystallized feldspar and hard hornblendic 

 material, with roundish specks of semi-crystallized feldspar. . . . 

 Remarkable for the regular parallelism of its lamination and 

 bedding ; the laminae alternately light and dark, being exceed- 

 ingly thin, many of them usually packing within the thickness 

 of an inch. In some of the layers certain laminae are studded 

 with isolated crystallizations of hornblende." "Occasionally the 

 rock approaches a porphyritic gneiss in aspect. . . . This has 

 much to suggest an igneous origin ; much of it is a true augen- 

 gneiss. ... It seems to resemble very closely the augen-gneiss 

 near Bedford, New York" (Rand, p. 278). 



The close association of groups of thin layers of hornblendic 

 schist, like sheared apophyses from a dike, observed on Man- 

 hattan Island,^ finds its analogues in this region : "Alternations 

 were observed of very soft schistose layers, one to eight inches 

 thick, of decomposed gneiss and mica schist, with layers of 

 small hard angular blocks of very hard, gneissoid gabbro- 

 diorite. Of the latter sixteen were observed in a space of eight 

 feet. . . . One dike (?) of it is about four feet in width " (Rand, 

 p. 288). 



These hornblendic schists show the same transitions as on 

 Manhattan Island to epidotic varieties ; biotitic granite ; highly 

 feldspathic gneiss, containing but little biotite or hornblende 

 (Frankford gneiss) ; biotitic gneiss, rich in black biotite, passing 

 into " a very quartzose biotite-schist, the layers being very well 

 defined and often 20 or 30 to the inch, and these layers exces- 

 sively plicated " (Rand, pp. 2^"] , 302). 



As to the serpentinoids, observations have shown that they 

 are all of the same geological horizon and mostly derived from 

 alteration of peridotite, amphibolite or pyroxenite (bronzite or 



' Rep. Prog., Second Geol. Surv. Penn., C6, pp. 28, 30, 92, 93, loi, 102, 114, 

 132. 



2Julien, loc. at., 471-474, 493. 



