324 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



casual couuectiou with fuinarole activity, using the term in a wide sense, 

 and indicates that the pegmatite dikes were tlie later products in the com- 

 plex series of granitic types present in the region. It has some analogy 

 with the fumarole products accompanying the trap eruptions in which, as I 

 have described (p. 423), albite, clearly water-deposited, rests on delessite in 

 amygdaloid cavities, as do also datolite, axinite, and rarely tourmaline — 

 boracic acid minerals. The cleavelandite, which is a variety of albite, and 

 abundant tourmaline match the minerals named above, but the analogy 

 does not extend to the rarer elements. 



DISTRIBUTION AND DESCRIPTION. 



Because of several ^peculiarities in the separate occuri'ences, I have 

 given below a description of each, commencing at the northwest and 

 going around the area by the south. 



I. THE (iREAT TOURMALINE-SPODITMENE DIKE. 



Macomber's spodumene ledge, Clarke's tourmaline ledge, the West 

 Chesterfield Hollow, and the well-known Walnut Hill spodumene ledges 

 (the last in what is now Huntington, the others in Chesterfield) are all 

 portions of one continuous or nearly continuous, A^ertical, interbedded dike 

 of coarse pegmatite, which is faulted and its south half thrown east at 

 West Chestei-field Hollow. 



A. A. Julien' says : 



At Macomber's ledge the coarse orthoclase granite of the main vein contains 

 films of margarodite and few imperfect green beryls, while in the secondary vein 

 the succession seems to have been, first, quartz, muscovite, granular albite, tourma- 

 line, and spodumene; then cleavelandite, quartz, manganese, garnet, and zircon; 

 and. finally, smoky quartz with green and blue tourmaline. The larger crystals of 

 most of these minerals penetrate through all the layers and their growth seems to 

 have been continuous. 



At Clarke's ledge the main granite vein is of the same general constitution 

 as at Macomber's, rarely showing a few large beryls. In the secondary vein no 

 sjiodumene occurs, but the succession is in the same order. First, on either wall a 

 saccharoidal albitic granite, with little quartz and mica and a few scattered, imper- 

 fect black tourmalines and garnets, then coarse cleavelandite, with blue, green, red, 

 and rarely brown tourmaline, and small quantities of the rarer minerals, microlite, 

 columbite, cassiterite, zircon, cookeite, lepidolite; all these, especially the tourmaline, 

 increase in quantity toward the center of the vein, which is filled up by an irregular 

 sheet of smoky quartz. 



' Spodumene and its alterations: Annals N. Y. Acad. Sci., Vol. I, p. 351. 



