PLATE VI. 



SECTIONS OF AMPHIBOLITES PROBABLY DERIVED FROM IMPURE LIMESTONES. 



Silurian. Drawn with lower nicols to show pleochroism. The upper nicol is used to bring out 

 the outlines of the grains in the colorless mosaic. The jjlane of polarization is parallel to the 

 long side of the plate. The hornblende grains are generally free from grains of the plagio- 

 clase. X 30. 



Fig. 1.— Maguetite-amphibolite. Conway schist. Whately. From the north end of the large band 

 near house of Mrs. M. Taylor. A black, slaty rock, easily mistaken for a black shale. A rock 

 of very fine and even grain. Many of the ore grains are surrounded by small groups of titanite 

 grains, many grains of which are scattered evenly in the whole field. A narrow vein filled with 

 large and long plagioclase grains, like the ground, crosses the slide. (See Analysis IV, p. 303, 

 and for description p. 194. ) 



FiQ. 2. — Rutile-epidote-amphibolite. South line of Guilford, Vermont. A shining-black schist, 

 slightly larger needles, black and lustrous, appearing among the others. A limpid granular 

 mosaic, in small quantity, no multiple twinning, rarely cleavage, one probable determination 

 of albite. Hornblende ragged-bordered, but without inclosures, with strong pleochroism and 

 cleavage. Much deep-red brown rutile clustering around black ore grains. Considerable pale- 

 yellow epidote. (See Analysis V, p. 303, and for description p. 195.) 



Fig. 3. — Epidote-amphibolite. Hawley series. Heath, near E. Gleason's. With large porphyritic 

 hornblendes and feldspars. A fine-grained, limpid feldspar mosaic, thick set with minute but 

 quite well-formed hornblende and rounded epidote grains. The large hornblendes show 

 remarkably strong pleochroism when viewed with a lens without the intervention of nicols, 

 and twinning, both of which properties are indicated in the figure. They are centrally 

 filled with minute foreign bodies. The feldspar crystals are centrally filled with liighly 

 refringent, slightly yellow grains of epidote, and the same are scattered through the ground. 

 The distinctly bounded feldspar cr}'stals are mostly broken into a mosaic. One shows trace of 

 Carlsbad twinning, but no cleavage or multiple t\vinning can be seen. The abundant grains 

 of magnetite show no trace of change. The red grains are much rusted ankerite. (See p. 166.) 



Fig. 4, — Amphibolite. Chester. From the cut nearest to the station. A black rock banded with 

 white layers, which are thin and interrupted, the mass of the rock made of shining, jet-black 

 needles just visible to the eye. Under the microscope the rock is very fresh, the hornblendes 

 are in long, ragged-ended, parallel blades with few inclusions and strong pleochroism. Extinc- 

 tion 21°. The coarse, limpid ground mosaic is made up of quartz and albite grains, polarizing 

 brilliantly and hardly distinguishable from one another, except that the quartz gives the black 

 cross and the feldspar is positive and biaxial. This mosaic resembles exactly that of the 

 adjacent sericite-schist. There is no trace of any other mineral except these three. (See 

 pp, 97, 160.) 

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