390 PROCEEDINGS OF THE AMERICAN ACADEMY. 



b. It may be regarded as assured, although the values for the two obser- 

 vations differ rather widely. 



w (025) was found on three crystals as a narrow face between o and c 

 and may be regarded as established. 



v (035) was observed but once as a faint line face between o and c. 

 Its position is fairly good, but it needs confirmation. 



Of the pyramids, p (111) was measured on two crystals and observed 

 on several others. It is always a distinct face giving brilliant reflections, 

 and is well established by the close agreement of measured and calculated 

 angles. 



t (112) and i (TI2) were each measured but once as narrow trunca- 

 tions of the edges between d and o and s and n respectively. The reflec- 

 tions were poor and the angular positions are not very close to calculated 

 values, but their positions in the zones and the fact that each was observed 

 several times, although with faces too narrow to give measurable reflec- 

 tions, seem to assure both of these forms. 



The drawings, each presenting a plan and a clinographic projection of a 

 crystal, illustrate the various habits of the Somerville babingtonite and 

 especially the occurrence of the new forms. Figure 3 is a simple combi- 

 nation particularly characteristic of the larger crystals. Figures 4, 5, and 

 6 are as nearly as possible in the proportions of the crystals on which the 

 various new forms were found. Figure 6, with the omission of the planes 

 u, x, and w, would reproduce very well the appearance of the majority of 

 the smaller crystals. Figure 7 is an ideal combination of all the forms 

 here described, and is represented as terminated below by the perfect 

 basal cleavage, which is very commonly developed. The gnomonic 

 projection, Figure 1, also brings out well the relations of the forms. 



Chemical Analysis. 



The material for analysis was obtained from a single large pocket of 

 prehnite in which the babingtonite was embedded in fine granular form. 

 The whole mass was roughly hand-picked, and the babingtonite crushed 

 and passed through a coarse sieve, washed to remove dust, and treated 

 with dilute acid to remove traces of calcite present. It was quite free 

 from limonite. It was then separated with an electro-magnet, which 

 readily attracted the babingtonite, leaving behind the prehnite and almost 

 all of the epidote, of which a very small quantity was present. After a 

 second treatment under the magnet with a slightly less powerful field, 

 the material was placed in methylene iodide at its maximum density, 3.34, 



