B. K. Emerson — The Deerfield Dyke and its Minerals. 355 



Tourmaline. — A single minute greenish-brown, hexagonal 

 rism with trihedral termination, which seemed to agree exactly 

 ith the sharper one, common in tourmaline, rested upon epi- 



Chalcopyrite. — Small particles of chalcopyrite and pyritec 

 plete the list, the datolite being generally exceptionally free 

 from enclosures. 



Botryolite. — One large cavity of the trap and nearly globu- 

 lar, with vesicular walls, was filled with datolite, which was 

 compact in the vesicles of the trap, above fine granular, like loaf 

 sugar and much gashed, and at the surface coated with a layer 

 ' Hilar botryolite, which would 

 , __ j had not proved fusible with ^ 

 flame before the blow-pipe. 



Hematite. — Occurs rarely in extremely minute, flat crys- 

 tals, blood-red by trans >n prehnite, and quite 

 tintadantly, as the coloring matter of the red diabase. 



Wad.— Occurs scattered over much of the prehnite in dots 

 often massed together over a surface otherwise clean, in long 

 diamond shapes, the shadows of elongated ealcite scalenohedra 

 which have disappeared. 



Cuprite.— In minute octahedra superficially altered into 

 malachite occurs on datolite and in a single case stains of mala- 

 chite upon prehnite. 



Hyalite. — A colorless hyalite of fine botryoidal structure 

 covers with a thick layer broad surfaces in the dark-gray dia- 

 base from the cuttings for the new road from Greenfield to 

 Turner's Falls, where also pearly- white botryoidal layers are 

 very abundant and seem in many cases to be of very recent 

 origin, and to have coated minute rootlets which had pene- 

 trated the fissures and lay across the botryoidal surface. 



The minerals of the third group, natrolite, stilbite, heulandite, 

 chabazite, analcite mid p\ rite, issocintcd still with ealeite and 

 fluor, appear after the forma 

 ceased entirely, and after n 

 veins by the action of water. 



Natrolite.-- -This mineral occurs in loose tufts of very 

 "iiiiat.c needles -01 to •|M»t""" in diameter, coating prehnite, 

 especially in those specimens whore epidote was abundant. It 

 was not found associated with datolite or any of the succeeding 

 minerals. The needles were colorless when fresh, but large 

 pieces of the rock were thickly covered with brown tufts of 

 apparently the same mineral which gave a black bead with the 

 Wow-pipe and seemed to be nearly transformed into limonite. 



