446 



Report of the State Geologist. 



The Highland Aeea of Gneissic Rooks. The following notes on the 

 Highland region are to be considered as merely preliminary and in the nature 

 of a reconnaissance. The crystalline rocks of this region present a most 

 interesting field for study, and it is hoped that opportunity will be afforded for 

 a further and more detailed consideration of their relations. Such detailed 

 work requires a most careful examination of all the outcrops and careful petro- 

 graphic examination with the microscope. Considerable has been published 

 hereupon in the report of Mather,* and certain portions of his work will be 

 referred to further on. Britton and Merrill also refer frequently to these 

 rocks in connection with their work on the Highland area in New Jersey.f 



Excluding the areas of gneiss forming the western half of Pochuck 

 mountain and another strip along the northwestern side of Bellvale mountain, 

 the gneissic rocks cover all of the townships of Tuxedo and Highland, and 

 about one-half each of those of Monroe, Woodbury and Cornwall. 



Tuxedo Township. The gneiss rises steeply along the eastern side of 

 Greenwood lake with a dip of 60° E. It is often massive, and sometimes 

 much shattered by joints at right angles to the stratification. These joints 

 not uncommonly represent fault planes. The gneiss is a mixture of quartz, 

 red orthoclase and hornblende. Specimens of this same gneiss, collected 

 from a point on the New York and New Jersey state line, were examined by 

 Professor Kemp in 1885 (JV. J. Geoi '. Surr., 1886, p. 102), and the orthoclase 

 found to be full of curious little inclusions. 



Northeast of Greenwood lake, the gneiss is strongly laminated and is com- 

 posed of biotite, feldspar and much quartz. The region between Greenwood 

 and Sterling lakes is heavily wooded and has not yet been examined. On 

 its eastern edge the rock along the shore of Sterling lake (346) is a dark- 

 colored, fine-grained basic gneiss. A section of the fine-grained portion of 

 this gneiss, from half way up the west side of the lake, shows it to consist of 

 plagioclase, hypersthene and magnetite. The plagioclase is in large plates, 

 fiesh. and full of beautiful apatite crystals. The hypersthene is strongly 

 pleochroic and the magnetite grains associated with it are large and rounded. 

 The dark, massive gneiss, one and one-half miles north of Sterling lake, may 

 be a continuation of this area (301). Sections of it afford much microperthite 

 and some quartz. 



The dark hornblendic gneiss surrounds most of Sterling lake and contains 

 the ore-bodies at the southeastern end of the lake. At this point are two 



♦Geology of New York, First District, 184'2. 

 t Geological Survey of New Jersey, 1885. 



