The Author desires to acknowledge gratefully the assistance 

 of the Carnegie Trustees, in the illustration of this concluding 

 volume of his work. Readers will see how extensive the 

 illustration of the three volumes has necessarily been, and will 

 share the author's gratitude in proportion as they find the 

 figures to aid the text. 



F. O. B. 



Jnne^ 1928. 



