ELIZABETHTOWN AND PORT HENRY QUADRANGLES 



53 



irregular masses of moderate size, and are sometimes demonstrably 

 in dikes. More often they seem to be irregular, eroded sheets, 

 knobs, or perhaps laccoliths. The abundant vegetation, the wide- 

 spread faulting, the extended erosion and the metamorphism, have 

 all served to mask the details. 



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AviOTtlra3Lte G&bbro 



^Syielss 



Fig^S Gabbro dike intruded in anorthosite and faulted. The gneiss is either an 

 inclusion or a dike older than the gabbro, and greatly sheared. The locality is in Lewis in 

 the northeast corner of Elizabethtown quadrangle. 



The rocks are greenish black in color and rough upon weathered 

 surfaces. The pitting from the decay and disappearance of the 

 feldspar has left the augite and ever present magnetite projecting 

 in little lumps. Where the gabbros appear in the beds of streams 

 and beneath cascades, the rock is a rich green and affords most 

 beautiful and instructive exhibitions of rock texture. It is com- 

 paratively rare that the gabbros are free from the effects of crush- 

 ing and shearing. When, however, such specimens are found they 

 present a coarse diabasic texture. The plagioclase crystals are tabu- 

 lar and on the fractured surfaces exhibit thin rectangular cross 

 sections within whose network the dark silicates and the iron ores 



