vi Preface. 
received from so many sources that I must leave 
the reference at the head of each locality to speak 
for itself, only acknowledging the special aid that 
has been given by Mr. James Bennie, in collecting 
the plants of the ancient silted-up lakes of the 
Scottish Lowlands. For the constant encourage- 
ment of Sir Archibald Geikie, Director-General of 
the Geological Survey, I am also very grateful. 
