240 DR JAMES GEIKIE ON 
merates but with other varieties of lava. But as this is not the case, it may be 
supposed that the whole vast series of basalt-beds and tuffs (13,000 feet or 
14,000 feet in thickness) accumulated upon the outskirts of an old volcanic 
area, They would, in this view, represent the heavier and more fluid lavas, 
derived from foci which may also have ejected agglomerates and many lavas of 
lighter specific gravity—these last having been unable to reach the great 
distances attained by the basalts. This would only be upon a larger scale than 
what we know has taken place in regions like Auvergne, where, as “in the Mont 
Dore, the trachytic currents,” according to Scropg, “ have in no instance flowed 
more than from 4 or 5 miles from the central heights of the volcanoes ; 
the basaltic currents, on the contrary, have reached a distance of 15 miles or 
more.” 
3. Miocene Age of the Strata: Physical Conditions under which they were 
amassed.—Although, as I have said, the plant-remains of Suderde have not been 
specifically determined, there is no reason to doubt that geologists are right in 
referring the igneous rocks of the Feerde Islands to the Miocene period. They 
almost certainly belong to the same great series of which the basalt-plateaux of 
Iceland, Greenland, Spitzbergen, and our own islands form separate portions. 
Such being the case, it may be allowable to offer a few remarks on the physical 
conditions under which the rocks of the Ferée Islands would seem to have 
been accumulated. 
We know that during the Miocene period there existed a very wide extent 
of land in northern regions. It is even highly probable that America and 
Europe were at that time connected, so that plants could migrate freely across 
broad areas which now lie drowned beneath the waters of the Arctic Ocean. 
It is not unlikely that during Miocene times land may have stretched con- 
tinuously westward from what are now the Ferde Islands to Iceland and 
Greenland. This belt of land must have been the scene of great volcanic 
activity, and we may conceive how after many successive sheets of lava had 
been poured out from one or more vents, or from long fissures, all the hollows 
of the old land-surface would be filled up for as great a distance as the molten 
rock flowed. If the lavas flowed from orifices like those of ordinary volcanoes, 
there may have been one or more central cones, rising probably to a consider- 
able elevation, and surrounded by vast plains that sloped outwards with a 
diminishing inclination in all directions. The cones themselves would be 
built up of irregular masses of different kinds of lava and heaps of more or less 
loose scorize, lapilli, bombs, and tuff. The same materials would also enter 
largely into the composition of the immediately adjacent low grounds. But 
the further one travelled from the centre of dispersion, the less abundant would 
lapilli and other loose ejecta become. Highly porous and scoriaceous lavas 
and clinkers would in like manner abound in the vicinity of the volcanic centre, 
