The Botany of Iceland - 01.12.1912, Side 40

26
H. JÓNSSON
The rocky coast is, as a rule, of solid rock, consisting of preglacial
basaltic lava. Postglacial basaltic Iava is found, nevertheless, in some
places, as for example on Snæfellsnes. In many places, large stretches
of the coast are covered with debris (Urð) from t'he mountains.
Where the debris or the new lava predominates the surface is ge-
nerally very uneven, and one then finds distinct elevations with
large and small depressions interposed; such a coast is usually
covered with an abundant and mullifarious algal vegetation, if the
conditions are in other respects favourable to the existence of algæ.
Tliere is no range of skerries (Skærgaard) as there is, for example,
on the coast of Norway. Yet a number of islands and rocks occur
in the fjords, especially in Breiðifjörður. In this fjord are found
indications of a range of skerries running parallel with the coast
and along a considerable stretch of it, and marking the outward
limit of the Zostera-\egetation.
The Sandy Coast. Almost the entire coast of S. Iceland is
sandy shore or gravel sliore. As a rule, such bottoms afford a mobile
substratum because eacli wave which breaks on the beach shifts the
particles backwards and forwards. A sandy coast is also met with,
here and there, in other parts of the country, but is then found,
as a rule, alternating with rocky parts; thus, the sandy or gravelly
shore is often predominant at the head of small indentations which
at the sides are bounded by projecting masses of rocks.
Clayey Shore is also found fairly frequently in the interior
of the fjords.
The rocky coast is, as a rule, abundantly overgrown, and this
is frequently the case also with the sublittoral gravel-bottom, while
the sand and gravel bottoms laid bare periodically by the shifting tide
are not, as a rule, overgrown, and, in any case, only with short-
lived species. On clayey and muddy bottoms, on the other hand,
algæ are seldom or never found, while Zostera often covers such a
bottom and forms submarine “green meadows.”
Despite the small “desert” areas, one may say that the coasts
are covered with a zone of continuous algal vegetation — if we ex-
clude the eastern portion of S. Iceland. This algal zone varies greatly
in width, accommodating itself to the precipitousness of the coast.
In a hay as shallow as Faxaflói the algal vegetation has a great
extension seawards, while it is far more limited, for example, on
the steeply descending submarine declivities in the fjords of the
east coast.