For the right to reproduce the photographs I am much indebted to the following gentlemen, to whom I express my warm thanks: viz. to the Rev. J. S. Lea, of Kirkby Lonsdale, for Plate VII. and fig. 149; to Prof. F. W. Oliver, of London, for Plate VI.; to Dr. O. V. Darbishire, of Manchester, for Plate IV. and fig. 130; to Prof. K. Fujii, of Tokio, for Plate III.; to Dr. F. F. Blackman, of Cambridge, for fig. 144; to Mr. Crump, of Halifax, for fig. 140; to Mr. R. Welch, of Belfast, for Plates I. and V., and fig. 138; to Dr. H. Bassett for figs. 154 and 155.

To Dr. W. E. Hoyle of Manchester, and to Miss Mary McNicol, B.Sc., I am also much indebted for their kindness in reading the proof-sheets.

I have drawn all the text illustrations specially for this book.

M. C. S.