542 



Report of the State Geologist. 



character of the gneiss, as exhibited in the township, is well shown. The 

 main 'portion is a well foliated rock of microperthitie mierocline and 

 orthoclase, with quartz and a variable, but commonly considerable amount of 

 hornblende, biotite and magnetite. Much basic hornblende gneiss is 

 interbanded with it. A mile and a half a little east of north of the Falls, in 

 a field a few rods back from the road, is a considerable exposure of a brown 

 gneiss which contains an orthorhombic pyroxene of too slight pleochroism 

 and too weak double refraction for hypersthene, and which is probably 

 enstatite. It is the only occurrence of this mineral yet noted in the county. 



A short distance to the east is a well foliated microperthitie gneiss holding 

 numerous garnets, a mineral which, as a rule, is quite rare in the gneisses. 

 Gneiss is well exposed for several miles along the valley of Great Black 

 brook, the best exposures being at Black Brook village. This gneiss is, for 

 the most part, a well-foliated plagioclase gneiss, containing also orthoclase, 

 some quartz and a considerable amount of hornblende, biotite and magnetite. 



The long ridge called Leggett mountain, w hich lies in the extreme south- 

 west and extends into Wilmington, Kssex county, shows frequent exposures 

 of red and lilac-grey mierocline gneiss at its northeastern extremity. Along 



