THE ANCIENT VOLCANOES OF GREA T BRITAIN 
xii 
cailic areas, and have now expanded the two Addresses by the incorporation 
of a large amount of new matter and of portions of my published 
papers. 
In the onward march of science a book which is abreast of our know- 
ledge to-day begins to be left behind to-morrow. Nevertheless it may 
serve a useful purpose if it does no more than make a definite presentation 
of the condition of that knowledge at a particular time. Such a statement 
becomes a kind of landmark by which subsequent progress may be measured. 
It may also be of service in indicating the gaps that have to be filled up, 
and the fields where fresh research may most hopefully be undertaken. 
I have to thank the Councils of the Eoyal Society of Edinburgh and 
the G-eological Society for their permission to use a number of the illustra- 
tions which have accompanied my papers published in their Trmisactions 
and Joimial. To Colonel Evans and Miss Thom of Canna I am indebted 
for the photographs which they have kindly taken for me. To those of 
my colleagues in the Geological Survey who have furnished me with informa- 
tion my best thanks are due. Their contributions are acknowledged 
where they have been made use of in the text. 
The illustrations of these volumes are chiefly from my own note-books 
and sketch-books. But besides the photographs just referred to, I have 
availed myself of a series taken by Mr. Eobert Lunn for the Geological 
Survey among the volcanic districts of Central Scotland. 
Geologioai, Survey Office, 
28 Jeemyx Stu,ef.t, London, 
Jamuiry 1897. 
