PLATE Vlllr. 



THIN SECTIONS OF MATERIAL FROM GREENFIELD AND MERIDEN "ASH BED." 



, 1. — Red hcmatitic trap with secondary albite in perfect twinned crystals lining the iuterior of 

 steam holes. Two large half-filled cavities and three smaller ones, wholly filled, appear. 

 The large porphyritic plagioclase to the right is mottled from decomposition. Green- 

 field, near Cheapside Village, at the electric railroad cut. See page 442. Magnified 20 

 times ; crossed nicols. 



, 2. — The interstitial aqueous deposit of plagioclase (probably albite), diopside, and a'gerine- 

 augite. The plagioclase has a dusty, altered center, caused by an early change to calcite 

 and a limpid exterior of later formation, which resembles the secondary plagioclase 

 of fig. 1. The diopside is marked by strong boundaries and distant cleavage. The 

 :cgeriue-augite is in dark patches. The darker bordering porti(ms are altered to serpen- 

 tine with development of cleavage. At the lower border patches of the black sand ajipcar. 

 At the top and right edge are isolated spherulites. Greenfield quarry, 20 feet above base 

 of bed. See page 434. Magnified 35 times ; crossed nicols. 



. 3. — Scoriaceous sandstone. The dark parts are the rusty sandstone, red in the interior of the 

 bands, and blackened by heat exteriorly. They show mud flow. The light parts are 

 irregular, limpid, plagioclase grains. The mud has shrunk away at the top from a first 

 growth of this kind, leaving a thin film of black grains, and in the narrow space a more 

 limpid, plagioclase growth occurs. In the center of the older growth is a highly refring- 

 ent mineral (datolite?), showing a micropegmatitic structure with the plagioclase. See 

 page 435. Greenfield, Cheapside cut. Magnified 20 times. 



. 4. — Greenish-brown glass with yellow borders, which are devitrified in series of small spherulites 

 with dark centers. The glass has been shattered, while the fragments were slightly 

 plastic. The fragments are in place in the slide, and the cavities are partly filled by a 

 secondary water-deposited albite growth. See page 432. From Meriden "ash bed," near 

 top on south path. Magnified 35 times. 



.5. — Hyalopilitic diabase from the Meriden "ash bed." Base formed of tufted, feathery, and 

 fasciculate groups of beaded threads. Large olivine at right, large augite full of glass 

 inclusions on left. Contact of basal bed on glass breccia. See page 436. Magnified 35 

 times. 



430 



