390 Leonard Hawkes—Building up the North Atlantie 
from subaerial denudation of the vesicular basalt surface like the 
laterite in India, because in Iceland they are very often found between 
basalts which have been poured out under the severest arctic climatic 
conditions.” 
The want of water and consequently plant, and animal en is 
forcibly brought home to the traveller in the Oda%ahraun, as the 
food which has to be taken for the horses seriously increases the size 
of the caravan and prevents any long absence from the grass lands. 
The lack -of plant and animal remains in the Tertiary red partings, 
which before had presented a rather pnzzling feature, is quite 
understood. Rivers hardly exist on the Oda%ahraun proper. The 
snows of the Dyngjufjoll, a ring of tuff mountains arising out of the 
desert, give birth to a few streams which soon lose themselves 
in the holes and gjds of the lava. The general absence of river 
courses and deposits in the Icelandic series, and indeed of the North 
Atlantic Tertiary volcanic series, is to be expected. Sir A. Geikie 
has described deposits and cuttings in the plateau of Western 
Scotland, due to rivers which are compared with those traversing the 
Icelandic desert of the present day (1, p. 229). In this connexion it 
must be remembered that practically all these rivers originate in the 
great Jokulls, and we have little evidence that ice-caps existed in 
Iceland in Tertiary times.'!. Even these Jokull rivers flow, not over 
the lava deserts, but rather over the sand and glacial deposits covering 
large tracts in the interior of the island, regions more representative 
of the thick interbasaltic series than of the red partings. The rivers 
which flowed over the Scottish plateau had their sources in the 
Western Highland mountains, which provided a large catchment 
basin sending forth rivers of such a size that they did not readily 
peter out on reaching the lava plains, but there is no evidence of any 
such high land bordering the Iceland region. 
During the building up of the greater part of the North Atlantic 
volcanic series-we conceive of immense lava plains, covered in places 
by loose fragmental products. These latter did not always remain 
stationary, but were liable to be caught up by the wind and carried 
long distances before being redeposited as a thin mantle covering 
large areas. This loose material was thrown up during the eruptions 
and also originated through abrasion of the tuff cones scattered over 
the plain, and in a subordinate degree from weathering of the 
scoriaceous surfaces of the lavas. In all probability these plains 
connected the New and Old Worlds, but commonly there was a dearth 
of rivers, plants, and animals, and no migration of these latter. 
At rare intervals vegetation gained a foothold, and ‘‘it is not _ 
improbable that the basalt plateaux might even be densely wooded ”’ 
1 Dr. Pjetursson has grouped the top series of the Tertiary basalts together 
as a ‘‘Graa Etage’’, and in them he has discovered ice-scratched surfaces 
which have led him to advocate the hypothesis of a ‘‘ Tertiary, possibly early 
Miocene Ice Age” (7, p. 99) The evidence is as yet too meagre for this 
hypothesis to be accepted with any certainty, though without postulating 
a change in absolute mean temperature it would be quite reasonable to 
imagine that glaciers were formed during the latter part of the volcanic period, 
eoneeunene upon the elevation of the plateau through successive outpourings 
of lava. 
