DOI Seite / Zitierlink:
https://doi.org/10.11588/diglit.748#0210
INVESTIGATIONS AT ASSOS, 1881. 167
age it stands between the first and second trachytes. The lime-
stone conglomerate to which reference has been made is older than
the third trachyte and younger than the second, upon which it rests.
These rocks, beginning with the oldest, will be described in the
order of their occurrence.
FIRST TRACHYTE.
This trachyte is one of the most abundant in the immediate
vicinity of Assos, and yet from the fact that it leaves few fragments
upon the surface it appears to be quite rare as compared with that
which forms the Acropolis. It is exposed in two large areas, one
south and the other northwest of the Acropolis, connected by a
narrow band extending across the hill in a southeasterly direction.
The prevailing color of this trachyte is purple, but it is frequently
modified so as to become yellowish or reddish purple, or even brick
red. In the compact and uniform ground-mass are imbedded nu-
merous minute feldspars never exceeding two millimetres in length,
and generally not half that size. They are either opaque white or
glassy, and never so prominent as to greatly modify the color of
the rock. Some of the feldspars are distinctly striated, but the ma-
jority of them are too small to determine with an ordinary lens.
There are small quantities of variously colored accessory minerals
scattered in the ground-mass, and others which are frequently
found in cavities or crevices. Among the latter hyalite is the most
common, occurring in beautiful botryoidal forms.
Of all the trachytes in this region no other preserves so well the
peculiarities of its surface at the time of eruption. The upper
portion is frequently very cellular and ropy, like that of modern
lava. The cells are of all forms and sizes, but are generally elon-
gated in such a way as to show the direction of motion when the
trachyte was extruded. They are sometimes drawn out in large
curves, indicating the manner in which the molten mass rolled down
the steep slope. A yellowish-colored substance lines many of the
cells, and they decrease in size and number downwards to a distance
of several feet from the surface, where the trachyte becomes very
dense. The direction of motion is frequently indicated also by a
stream-like arrangement of the porphyritic crystals of feldspar. Oc-
casionally there are imperfectly developed joint planes parallel to
age it stands between the first and second trachytes. The lime-
stone conglomerate to which reference has been made is older than
the third trachyte and younger than the second, upon which it rests.
These rocks, beginning with the oldest, will be described in the
order of their occurrence.
FIRST TRACHYTE.
This trachyte is one of the most abundant in the immediate
vicinity of Assos, and yet from the fact that it leaves few fragments
upon the surface it appears to be quite rare as compared with that
which forms the Acropolis. It is exposed in two large areas, one
south and the other northwest of the Acropolis, connected by a
narrow band extending across the hill in a southeasterly direction.
The prevailing color of this trachyte is purple, but it is frequently
modified so as to become yellowish or reddish purple, or even brick
red. In the compact and uniform ground-mass are imbedded nu-
merous minute feldspars never exceeding two millimetres in length,
and generally not half that size. They are either opaque white or
glassy, and never so prominent as to greatly modify the color of
the rock. Some of the feldspars are distinctly striated, but the ma-
jority of them are too small to determine with an ordinary lens.
There are small quantities of variously colored accessory minerals
scattered in the ground-mass, and others which are frequently
found in cavities or crevices. Among the latter hyalite is the most
common, occurring in beautiful botryoidal forms.
Of all the trachytes in this region no other preserves so well the
peculiarities of its surface at the time of eruption. The upper
portion is frequently very cellular and ropy, like that of modern
lava. The cells are of all forms and sizes, but are generally elon-
gated in such a way as to show the direction of motion when the
trachyte was extruded. They are sometimes drawn out in large
curves, indicating the manner in which the molten mass rolled down
the steep slope. A yellowish-colored substance lines many of the
cells, and they decrease in size and number downwards to a distance
of several feet from the surface, where the trachyte becomes very
dense. The direction of motion is frequently indicated also by a
stream-like arrangement of the porphyritic crystals of feldspar. Oc-
casionally there are imperfectly developed joint planes parallel to