352 B. K. Emerson — The Deer field- Dyke and its Minerals. 



CALCITE. — Of the minerals which succeed to the prehnite, cal- 

 cite and datolite are the most important and most abundant 

 and generally replace each other in different veins. In some a 

 large development of calcite occurs with much axinite, in 

 others an equally large development of datolite. The axinite 

 shows that boracic acid was not wanting during the formation 

 of the prehnite and during the subsequent increase of the 

 calcite in the veins where the datolite fails to appear, and the 

 presence of epidote and the more abundant development of 

 prehnite indicate more elevated temperature in the latter, while 

 in the other veins the supply of boracic acid was greatly in- 

 creased so that nearly all the calcite was absorbed in the for- 

 mation of datolite. 



Excepting quartz all the minerals enumerated above as 

 enclosures in prehnite occur as enclosures in the calcite which 

 follows it, and when pieces where the latter is abundantly de- 

 veloped are thrown in acid and the calcite nearly dissolved 

 away, specimens of great beauty are obtained, the delicate 

 frost-work of prehnite, chalcopyrite, epidote, and the black 

 stout axinite being set off against the brilliant luster of the 

 etched calcite, the whole being sprinkled over with minute 

 pale green dodecahedra of flu or. It occurs abundantly in dis- 

 tinct crystals and drusy surfaces over the prehnite; -£R small 

 with rounded edges; V bristling over large surfaces; T, 0, 

 411 /, I s , with curved and striated faces; l 12 with deeply striated 

 faces and often distorted ; 1', ~\\ the lirst striated parallel to 

 - { ,\i. and the form either acuminate or truncated by a single 

 face of K. Other delicately suspended forms had at one end 

 a single broad face of R and rose in a group of sharp scaleno- 

 hedra at the other end. Every where the crystals were small 

 and affected the most elongate forms with rounded edges and 

 rounded, striated and distorted faces, as if to imitate as closely 

 as possible the prehnite with which they were associated, 

 while on the datolite the forms 2R or -2R, R invaria >U a] - 

 pear in large perfect I v transparent crvstais up to 18 mm in 

 length, and with a luster e<iual to that of the datolite itself. 



IUtolitk.— The datuliie is second or.lv to prehnite in 

 abundance at the new cutting and mi, p <sm- all the ..uncials 



the light gray diabase. The mineral 



pletely with a white saccharoidal deposit from 10 to 50 mm 



thick,' with only here and there cavities in which line crvstais 

 have come to development It rests sometimes upon the trap 



