Acta naturalia Islandica - 01.02.1946, Síða 43

ORIGIN OF THE BASIC TUFFS OF ICELAND
37
bottom of the valley was swept like a floor, and was left without
stumps or roots to indicate its previous forest cover. It was hard
to find even a pebble in that area greater than a few iriches in dia-
meter. In the lower reaches of the valley this floor still carries its
covering of baked mud flow, sometimes 2 or 3, sometimes 5 or 6 feet
deep, and it is only when one arrives at the far end of the devastated
region that the disposition of the boulders from the summit and
the timber which once covered the valley begins to be evident. Here
are giant trees broken and twisted into fantastic groups, with here
and there a boulder weighing up to 15 tons or more. As statcd above
this cleaning-out of the timber cover of the valley was not accom-
plished in the first instance by the mucl flow, because the valley walls
are clean far above any point reached by the mud. It requires hardly
more than a glance, however, to show what the agent must have been,
for higher up on the inclosing sides of the valley, a little at the side
of the main axis of the blast, we find the forest trees down but not
removed, and in particular we find them lying in parallel rows for
nearly 2 miles, with their tops pointing uniformly away from the
crater”. “Another interesting observation may be made in the outer
zone at side of the blast. Most of the trees which line these
corridors were uprooted, but some were broken off a few feet above
the ground instead. The standing stumps of such bear unmistak-
able, direct evidence of the bombardment which they received. With-
out exception, their bark is gone on the side toward the mountain,
while fully retained on the protected side. Similarly, the exposed
wood on the side toward the mountain is completely peppered with
fine sand, oftentimes driven in for a considerable fraction of an
inch. Indeed, as one nears the source of the outburst the intensity
of this bombardment was that of a fierce sand-blast which rounded
off the stumps themselves.” (p. 22—24).
It would seem a very reasonable conclusion that a blast laden with
sand and rock fragments such as this one would file and scratch
the surface of a basaltic lava and create a surface which locally
might show striking similarities to a glacially striated surface.
Furthermore, it would not be surprising to find in a subsequent
mud flow a low percentage of scratched blocks.
Summing up, we see that the Icelandic conglomerates possibly have
analogues of volcanic origin, either consisting of directly erupted
material or of material which was worked and depositecl as a second-