?. K. Emerson — The Deerfield Dyke and its Minerals. 



dules in this rock i 



albite, with datolite, pyrite or globules of zinc blende. 



Historical— Already in 1818* President Hitchcock noticed 

 several of the zeolitic minerals enumerated below, with a word 

 in each case as to mode of occurrence, and mentions as locali- 

 ties one mile E. 2° 15' S. from Deerfield Academy, and the 

 copper veins opposite Turner's Falls. In 1826f he described 

 a mineral from the mouth of Fall River near Turner's Falls 

 as the chlorophaeite of Macculloch. In the final report on the 

 Geology of M ssacl isetts. pp. 203, 660, he enumerates the min- 

 erals there known without increasing the former list: barite, 

 copper, malachite, chalcocite, chaleopyrite. chluritc. chioivpha - 

 . augite, quartz and varieties, selenite, chab- 



A few years ago railroad cuttings on the north side of the 

 Deerfield River at Cheapside exposed veins of massive datolite 

 3 to 4 cra wide, which showed no distinct crystals and occurred 

 without the minerals which commonly accompany it, excepting 



During the summer of 1880, a heavy cut was- made through 

 the corresponding portion of the dyke on the south side of the 

 river for the extension of the Canal Railroad, and opened up 

 veins carrying the usual trap minerals in great abundance and 

 beauty. These veins run nearly vertically, with a thickness 

 not above 10 cm , and were exposed to a depth of above 18 mm . I 

 propose to describe the minerals in the order of their occur- 

 rence in the veins and to discuss at some length their paragene- 

 sis and the crystallography of several of them. 



Diabantite.— The chloritic mineral, so uniformly and abund- 

 antly disseminated in the diabase of the valley, was entered in 

 the catalogue of the State collection by Dr. Hitchcock as foli- 

 ated chlorite, Turner's Falls, and a paler pulverulent variety, 

 as earthy chlorite, Springfield. A third mineral, intimately 

 associated with these follows them in the collection under the 

 name chlorophocite, a misprint for chlorophasite, Gill. The 

 latter is for the sake of symmetry made to follow prehnite, it 

 being a product of the decomposition of the latter mineral. 

 That the former mineral is chemically identical with that ana- 

 lyzed by Hawes and named diabantite by him, is extremely 

 probable in view of their identity in all physical and especially 

 optical properties, and of the monotonous similarity of the 

 many diabase dykes of the Connecticut basin, in which both 

 occur. That the mineral is distil as the word 



is used by Zirkel, Rosenbusch and Heddle, is much less certain. 



* This Journal, i, 115, 116. + This Journal, x, 393. 



