236 BULLETIN OF THE 



cavity and are distinctly separated from it. They are filled with epi- 

 dote, chlorite, calcite, quartz, and a fibrous chalcedouic (1) material : 

 the epidote is generally on the outside, the chlorite inside. Consider- 

 able epidote is scattered through tlie section, generally outside of the 

 feldspars, and also talc, calcite, and quartz. These decomposition prod- 

 ucts often occur in the groundmass in rounded areas, but are not true 

 amygdaloids. Patches of reddish opaque ferrite also occur in a similar 

 manner, constituting the red spots seen macroscopically. 



[".5.] Western Ridge of the Dike on the West Side of a Road which crosses 

 it, — to.ken towards the Centre of the Mass. 



Lens. A greenish groundmass containing porphyritic feldspars, red- 

 dish and greenish areas of alteration, and rounded masses of quartz. 

 The groundmass has intruded into some of the large feldspars. — 

 Section. Crystals of feldspar and areas of decomposition or infiltration 

 surrounded by a greenish chloritic mass. The large feldspars are occa- 

 sionally Carlsbad twins ; the small ones of the groundmass principally 

 plagioclase, although some are twinned sanidin crystals. The (original) 

 base, carrying small feldspars, has bent some of the large feldspars, and 

 pushed into them. Others contain in the centre square zonal inclusions 

 of the greenish mass, while the outer zone of the crystal is free from 

 it. These phenomena are similar to those so frequently observed in the 

 unaltered basalts with a glassy base. Many of the larger feldspar crystals 

 are partly filled with epidote grains, chloritic material, and light-green 

 needles, which have a yellowish-white polarization. Rounded areas, com- 

 posed of greenish chloritic fibres, with sometimes a deep violet blue 

 color between crossed nicols, occur in the groundmass, mingled occa- 

 sionally with talc, and bordered by epidote. Some of these areas, en- 

 closing the remains of the small feldspars, arise from the decomposition 

 of the groundmass ; others are either true amygdulcs, as described above, 

 or some might be pseudomoi-phs after some mineral, — for instance, oli- 

 vine. Between the feldspars lies the gi-een mixture of chlorite, viridite, 

 and greenish needles similar to those described in the feldspars, beside 

 some epidote, calcite, and quartz. 



[6.] Western Ridge of the Amygdaloid, about fifty feet east of a Road 

 crossing it, — the Specimen taken from a long Dike crossing the 

 Amygdaloid obliquely to its Main Trend. 



Lens. A grayish-green groundmass, holding crystals of greenish 

 feldspar and grains of pyrite. The groundmass has pushed into some of 



