6 
INTRODUCTION 
BOOK I 
ineasiu’e those ot eruptions under the sea. In studying them we are per- 
mitted, as it were, to explore the sea-bottom. We can trace how sheets of 
coral and groves of crinoids were buried under showers of aslies and stones, 
and how the ooze and silt of the sea-floor were overspread with streams of 
lava. We are thus, in some degree, enabled to realize what must now 
happen over many parts of the bed of the existing ocean. 
The geologist wlio undertakes an investigation into tlie history of 
volcanic action within the area of the British Isles during past time, with a 
view to the better comprehension of this department of terrestrial phy-sics, 
finds himself in a situation of peculiar advantage. I’robably no region on 
tlie face of the globe is better fitted than these islands to furnish a large 
and varied body of evidence regarding the progress of volcanic energy in 
former ages. This special fitness may be traced to four causes — 1st, The re- 
markable completeness of the geological record in Britain ; 2nd, The geographical 
}iosition of the region on the oceanic border of a continent; :5rd. The singu- 
larly ample development to be found there of volcanic rocks belonging to a 
long succession of geological ages ; and 4th, The extent to which this full 
chronicle of volcanic activity has been laid bare by denudation. 
1. In the first place, the geological record of Britain is singularly com- 
plete. It has often been remai'ked how largely all the great periods of 
geological time are represented within the narrow confines of these islands. 
The gaps in the chronicle are comparatively few, and for the most part are 
not of great moment. 
Thanks to the restricted area of the country anil to the large number of 
observers, this remarkably full record of geological history has been studied 
with a minute care which lias hardly been equalled in any other country. 
The detailed succession of all tlio formations has been so fully determined 
in Britain that the very names first applied here to them and to their sub- 
divisions have in large measure passed into the familiar language of geology 
all over the globe. Every definite platform in the stratigraphical series 
lias been more or less fully worked out. A basis has thus been laid for 
referring each incident in the geological liistory of the region to its proper 
relative date. 
2. In the second place, the geographical position of Britain gives it 
a notable advantage in regard to the manifestations of volcanic energy. 
Basing from the margin of a great ocean -basin and extending along the edge 
of a continent, these islands have lain on that critical border-zone of the 
terrestrial surface, where volcanic action is apt to be most vigorous and 
continuous. It has long been remarked that volcanoes are generally jilaced 
not far from the sea. From the earliest geological periods the site of 
Britain, even when submerged below the sea, has never Iain far from the 
land which supplied the vast accumulations of sediment that went to form 
the Bakeozoic and later formations, while, on the other hand, it frequently 
formed part of the land of former geological periods. It was thus most 
favourably situated as a theatre for lioth terrestrial and submarine volcanic 
activity. 
