B. K Emerson— The Deerfield Dyke and its Minerals. 275 



Farmington be referred to the acute angles of the arrow-head, 

 to recur to the first explanation given above, they would have 

 the more complex formula i'-6£. Furthermore, the two well- 

 scribed above form by their intersections 

 diamonds with the acute angles (80°) at top and bottom, while 

 the larger angle is at the sides, while the drawing of M. Des- 

 s * shows the reverse to be the case in the crystals 

 from Farmington. 



That is, in the first they are parallel to b' and b" (fig. 1), 

 while in the second case, if they were exactly the reverse, they 

 would be parallel to the short axes a' and a" ; but they are 

 stated in the later article of M. DesCloizeaux to make an angle 

 not of 80° but of 82° with each other, so that while one is par- 

 allel to a short axis, the other is | hetical face, 

 t-6. If they made an angle of exactly 80° with each other, 

 they would represent the horizontal striation of the central 

 the faint second striation described in the Deerfield 



s as siioliilv indicated at the bottom c 

 are difficult of 



■ 



b. In am)j<i<htl<,i<h<J <:ariti<-s. — The amygdules of the trap quite 

 closely repeat in miniature the occurrences of the large fissures, 

 uliar changes the prehnite undergoes in the former 

 '', needful to discuss separately its modes of appear- 

 In the coarse diabase it occurs compact, of a bright green, as 

 if colored by copper. The pangenesis is (1) diabantite, (2) 

 chaleopyrit.e. pvnte, .u'alena, prehnite, one or all, (3) calcite. 



In the red diabase, so abundant in the upper part of the 

 dyke through Greenfield and Gill it appears in spherical and 

 spheroidal balls 12-15 mm in diameter, very fine-fibrous and 

 sati n v. and very pale green to colorless; coated, and for a 

 distance in impregnated with diabantite. \t is radiated fine- 

 fibrous, the fibers not easily separated, and diverging from 

 several centers and meeting along sharp suture lines, so that 

 only parts of spheres result, and if water-worn the grains would 

 form perfect chlorastrolites. 



In the dark urav diabase from the north side of the Deerfield 

 and on through Greenfield and Gill, cavities l0-3b mm across are 

 -•mciiiii.^ filled with tibrous prehnite, the whole blackened as 

 if it had been held in the flame of a candle. Under the micro- 

 scope the fibers are, for the most part, perfectly fresh, and up 

 through the spaces between them has penetrated a black 

 amorphous powder looking like the beard of iron filings on a 

 magnet, or like a network of soot-covered cobwebs. The 

 whole seems to be dendritic in character. 



