Fróðskaparrit - 01.01.1977, Blaðsíða 168

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Glacial striae, roches moutonnees and ice movements
Tertiary. The total thickness of the basalt plateau is about
3000 m., and it may be divided into 6 sections which reflect
the progress of volcanic activity and the chronological age of
the series: 1. the lower basalt series (ca. 900 m.), 2. the coal-
bearing sequence, 3. the tuff-agglomerate zone, 4. the middle
basalt series (ca. 1350 m.), 5. the upper basalt series (ca. 675
m.), and 6. minor intrusions (Rasmussen & Noe-Nygaard
1969, 1970).
The major landscape features are strongly influenced by the
structures in the three basalt series mentioned above, so that
each of them has its characteristic landscape type.
The lower basalt series is built up of thick, compact lava
flows with an average thickness of ca. 20 m. The flows are
separated by intercalated, less resistant tuff-clay strata. Weath-
ering thus produces a broad step-like landscape, with steep
terminations of exposed basalt flows and evenly-sloping vege-
tation-clad surfaces.
In the middle basalt series the lava streams are thin, with
extremely porous intermediate zones, and the series is thus
very little resistant to weathering processes. As these pro-
cesses are more severe at higher altitudes, the washing-down of
weathered material will result in a smooth, convex land form,
since the streams are usually so thin that they rarely occur as
lava benches.
In the upper basalt series we again find the structure of the
lower series: alternating layers of basalt and tuff, but since
neither the basalt nor the tuff layers are as thick here as in the
lower series, the step-like landscape here is made up of smaller
steps.
Where they occur, the coal-bearing sequence and the tuff-
agglomerates form uniform, vegetation-clad slopes between the
lower and the middle basalt series.
Suðuroy.
Suðuroy is the most southerly of the Faeroe Islands, about
32 km. long, with a maximum breadth of about 13 km. It has
an area of about 166 km2.