B. K. Emerson— The Deerfield Dyke and its Minerals. 359 



built up has reached here an unusual complexity. The crys- 

 tals are commonly twinned on 0, and in three cases very per- 

 fect twins, composition face i?, occur, both halves being devel- 

 oped to perfect rhombohedra. In a single instance the apex of 

 a crystal is replaced by three large deeply striated faces of a 

 'latter rhombohedron apparently -J. The s'trise run parallel to 

 the combination edge of R and i, and arc piainlv formed by 

 the oscillatory combination of \ and 0. The character of the 

 face did not allow accurate measurement. In thin fissures it 

 encrusts broad areas producing a tessellated surface made up 

 of a great number of flattened crystals showing each a single 

 face of i?, the adjacent ones being in twin position and the 

 whole reflecting the light together like a single face of a very 

 large crystal. 



The paragenesis of the stilbile-chabazite veins is— 



•Below is a general table of the paragenesis oi I 

 found. The oldest is first, and the overlap of the 

 sponds approximately to the overlap of the minera 



% 



