122 REPORT ON THE GEOLOGY OF ESSEX CO., MASS. 



is much biotite. There are also local variations in color 

 due to inclusion of other minerals in the feldspars. The 

 Pigeon Hill and Lanesville granitites are of a greenish 

 color, while the granitite from Wenham and Ipswich is 

 grayish white. In a few areas the quartz is in excess 

 while in others there is little quartz which is of a smoky 

 color. Examples of this are seenin the upper opening of 

 the Rockport Granite Company's quarry at Rockport. 

 Thin sections of this hornblendic-granitite when stuclied 

 with the microscope show it to be composed of thefollow- 

 ing minerals : orthoclase, microcline, microperthite which 

 is composed of simple twinned albite crystals intergrown 

 across the twinning plane of the microcline, hornblende 

 of the green variety, sometimes altered to glaucophane, 

 much quartz and biotite ; with biotite, fluorite, garnet, 

 zircons, actinolite and magnetite as accessory minerals in 

 the feldspars. Nearly all of the rocks of this formation 

 show evidence ot snbjection to a great strain or crushing 

 force, as most of the original minerals have numerous 

 cracks which have been filled with a secondary formation, 

 either biotite or glaucophane. 



Minerals in the thin sections from the Cape Ann Gran- 

 ite Company's qnarries are as follows : quartz in large 

 patches which is greatly cracked and crnshed, orthoclase, 

 microcline, some plagioclase, microperthite, hornblende, 

 a little biotite, some muscovite, large patches of mag- 

 netite, some quite large microscopic zircons, epidote and 

 limonite. The feldspars are much decomposed. This 

 section is nearly identical with sections of the same rock 

 from Wenham, Hamilton and Ipswich. 



No. 2. Granophyric-Granitite ; Contact Zone. 



This rock formation is quite variable in texture accord- 

 ing to its position in the rock-mass. Near the exact con- 



