1 14 NATURE NOTES 
exposed, then its “ igneous character can of course be 
detected. 
Numerous beds or strata of various kinds of igneous rocks 
are found to be alternating with clays, &c., pointing to the fact 
that the volcanoes which poured them forth were under the sea ; 
so that the clays were afterwards deposited upon the beds of 
lava. Then the whole became subsequently upheaved, forming 
dry land, so that the old sites of the volcanoes can now be 
discovered by geologists. As examples of elevated igneous 
rocks, Cader Idris, near Barmouth, has its summit composed 
of consolidated rocks, once molten ; but the actual formation 
of the crater is all gone. 
Existing volcanoes may be either isolated as gigantic cones, 
with smaller ones formed on their sides, as Vesuvius ; or they 
may be clustered and sm^all, called Buys. These were soon 
burnt out and are now extinct. They have often converted their 
craters into lakes. Such may be seen in the Eiffel district near 
Coblenz. 
Vast plateaux formed by the out-pouring of lava constitute 
a distinct feature in some modern volcanic districts, such as 
Iceland. Nothing of the nature of a conical volcano now exists 
in the British Isles. \Vho would suspect that Devonshire was 
once and for long ages the scene of great and numerous active 
volcanoes ? So completely have they disappeared that it is only 
the harder rocks which have resisted denudation to a rather 
greater extent than others, so that elevations are left, forming 
an undulating country, covered with orchards, beneath which 
lie the remnants of the old vents. 
Similarly in Scotland numerous submarine volcanoes poured 
out their lavas, now recognisable in the uplands and moorland 
districts, &c. 
As examples of old “ necks ” of volcanoes, Arthur’s Seat, near 
Edinburgh, is one ; the Bass-rock, near the shore of Canty Bay, 
and Penmaenmawr, are others. 
One of the most remarkable features of volcanic rock is the 
columnar character of basalt, which is lava cooled slowly. It 
is well seen in Fingal’s Cave, and clusters of pillars arise out of 
the ground near the top of Cader Idris. A large quarry is full 
of them near the Rhine, and the pillars are used for posts all 
along the bank near Coblenz. 
Although ancient volcanoes, as far as they are preserved in 
our islands, afford no striking or characteristic features, the 
causes which gave rise to the explosive outbursts forming 
volcanoes, may play a very important part in the upheaval of 
rocks, crumpling and contorting them, and so finally making 
important scenic effects, as we all know in Switzerland. 
It may, therefore, be desirable to explain briefly why vol- 
canoes arise at all. 
* From the Latin i^nis, fire. 
