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



chabazite . I witb it, show entirely fresh 



faces. It is the lincolnite of President Hitchcock, and the 

 specimens studied by me agree exactly with those labeled 

 lincolnite by him, and coming from the old locality east of 

 Deerfield. The mineral collection at Amherst contained a few 

 crystals, also identical with the above, from the Fitchburg cut- 

 ting, and these were separated by Professor Shepard from heu- 

 landite under the name lincolnite.* 



After careful study I find all these crystals identical with 

 each other and with heulandite, both optically and crystallo- 

 graphically. 



Analcite. — Occurred (a) in a single cryst il upon prehnite ; 

 (b) in flat eight-sided plates 10-12 mm across, striated and formed 

 by the growth of the trapezohedron, in a narrow fissure ; (<?) 

 in milk-white tilms circular and octagonal, 5-10 mm across; 

 (d) in extremely fine botryoidal surfaces with crystalline struc- 

 ture, with here and there a system of curious concentric 

 depressed rings, like the siliceous annulations on sonic fossils 

 (Beckite). They are as if formed by pressing several rings 

 each smaller than the other into a soft mass, so that it should 

 rise as a series of thin concentric combs between them, (e). 

 Other pieces which seem to me to have been analcite of the 

 form (b) are now wholly decomposed into a yellow ferruginous 

 kaolin (?). 



Associated with the analcite (b) and resting against the sepa- 

 rate crystals on all sides is opaque white calcite, \R and I 6 , 

 grouped in parallel clusters, the laces all rounded and the clus- 

 ters looking as if they had been made of some soft material 

 which had "run." This grouping of the calcite around the 

 separate crystals of the analcite may explain the annulations 

 mentioned above, the two minerals having increased alternately 

 and the calcite afterward having been removed. 



Chabazite. — At Cheapside it occurs in small pellucid rhom- 

 bohedra with delicately striated faces. Crystals l mm in 

 length. It rests always upon the trap and never upon the 

 heuhmdite with which it is associated, though when they 

 come in contact the latter penetrates the chabazite and is the 

 older mineral. 



Farther south, east of Old Deerfield, it occurs in the same 

 association. Most of the specimens agree in all respects with 

 those already described but are whitened and opaque from in- 

 cipient decomposition. Rarely much larger crystals occur 

 which are 6-8 mm in length. These are quite fresh, the faces 

 of good luster but faceted in a very intricate manner, indicat- 

 ing that the twinning by which the apparent rhombohedra are 

 * C. U. Slier' a 75 miles of Amherst Col- 



