422 



GEOLOGY OF OLD HAMPSHIRE COCTXTY, MASS. 



well-tbrraed plagioclase twins of earliest cousolidatioii, Avliich are, as usual, 

 dusted with impurities, or decomposition products, and a few fine rods of 

 later growth, and these constituents are entirely like those found in the 

 normal trap. They are, however, not accompanied by magnetite and augite. 





.-> 





^'^"-'--s^ 

 ■■-* * -m:' 



-'^ 



Fio. 24. — Thin sections of sand and glass breccia {A, B) from the base of tlie Greenfield sheet at the city quarry and of 

 trap (0) from Cheapside. Drawn by Charlotte F. Emerson. A X 30. J? X 85. 0X30. 



as in the normal trap, but are included in an olive-green streaky and hardly 

 differentiated magma, which is often thrust in among the sand grains where 

 the feldspar can not follow. Large trap fragments appear at the right of 

 A and B. 



The third constituent of the rock, and a most interesting one, is of 

 aqueous or igneo-aqueous origin, it being plainly formed by the action 



