vi NOTE 



writing the preface and the footnote on p. 45 to which his name 

 is appended. I am also under great obligations to Professor A. C. 

 Seward, F.R.S., for valuable criticism, and to Dr W. T. Gordon 

 for advice on questions relating to Scottish Geology. The por- 

 trait which forms the frontispiece of this book is reproduced by 

 kind permission of the Editor of the Geological Magazine. 



I have to express my gratitude to the Council of the Royal 

 Society for a grant in aid of the preparation and publication of 

 my husband's manuscripts. 



AGNES ARBER. 



