DOI Seite / Zitierlink:
https://doi.org/10.11588/diglit.748#0220
INVESTIGATIONS AT ASSOS, 1881. 177
THIRD TRACHYTE.
The third trachyte, which appears to be the prevailing rock in the
southern part of the Troad, is represented in the immediate vicinity
of Assos by an area southeast of the Acropolis so small that it
scarcely appears upon the map.
It is usually dense, and of a reddish or purplish-brown color.
The groundmass, as in the first trachyte, forms the greater portion
of the rock. In it are imbedded numerous small crystals of feld-
spar, many of which are glassy, while others are opaque white and
irregular in outline. A few small flakes of mica are scattered
throughout the rock, and apparently also a few grains of quartz.
The formation is frequently cellular, but not because of the expan-
sion of gases, as in the first trachyte. The cells are elongated and
irregular in outline, having rough surfaces, as if produced either by
the decomposition of minerals or by the flowing of the mass at the
time of its extrusion. These cavities are frequently of considerable
size, especially where the trachyte contains many fragments arranged
parallel to a well-marked fluidal structure. Associated with this
trachyte is a very interesting glassy rock, containing more or less of
a black substance quite like obsidian in its general aspect, but dull,
softer, and breaking easily into small pieces. Occasionally the
formation is almost wholly composed of this vitreous material, con-
taining opaque white crystals arranged in parallel lines.
The relation of the second and third trachytes is not so readily
determined as that of the first and second. The superposition of
the third trachyte upon the second was clearly seen at a locality
Fig. 2.
1. --"~"~
I. Third Trachyte. II. Second Trachyte.
about one kilometre east of Assos. At this place the fluidal struc-
ture of the third trachyte is well developed. The annexed figure
12
THIRD TRACHYTE.
The third trachyte, which appears to be the prevailing rock in the
southern part of the Troad, is represented in the immediate vicinity
of Assos by an area southeast of the Acropolis so small that it
scarcely appears upon the map.
It is usually dense, and of a reddish or purplish-brown color.
The groundmass, as in the first trachyte, forms the greater portion
of the rock. In it are imbedded numerous small crystals of feld-
spar, many of which are glassy, while others are opaque white and
irregular in outline. A few small flakes of mica are scattered
throughout the rock, and apparently also a few grains of quartz.
The formation is frequently cellular, but not because of the expan-
sion of gases, as in the first trachyte. The cells are elongated and
irregular in outline, having rough surfaces, as if produced either by
the decomposition of minerals or by the flowing of the mass at the
time of its extrusion. These cavities are frequently of considerable
size, especially where the trachyte contains many fragments arranged
parallel to a well-marked fluidal structure. Associated with this
trachyte is a very interesting glassy rock, containing more or less of
a black substance quite like obsidian in its general aspect, but dull,
softer, and breaking easily into small pieces. Occasionally the
formation is almost wholly composed of this vitreous material, con-
taining opaque white crystals arranged in parallel lines.
The relation of the second and third trachytes is not so readily
determined as that of the first and second. The superposition of
the third trachyte upon the second was clearly seen at a locality
Fig. 2.
1. --"~"~
I. Third Trachyte. II. Second Trachyte.
about one kilometre east of Assos. At this place the fluidal struc-
ture of the third trachyte is well developed. The annexed figure
12