viii THE VOYAGE OF H.M.S. CHALLENGER. 



Appendix B. consists of a paper by Professor Renard on the Petrology of 

 St. Paul's Rocks (Atlantic). 



A peculiar interest has been attached to these rocks since Mr. Darwin 

 expressed a belief that they were not volcanic. 



Shortly after the return of the Challenger, I formed the opinion that 

 they were of eruptive origin, chiefly because I believed fluxion structure could 

 be observed in many of the microscopic sections of the rocks. 



As it was of great importance to have the opinion of an experienced 

 Petrologist, all the materials and observations were placed in the hands of 

 Professor A. Renard, who has discussed the whole question with great ability. 

 In the narrative volume several photographs of the rocks will be given. 



It was originally intended to issue this volume at the same time as 

 Volume I., containing the narrative proper of the voyage. Since, however, 

 Vol I. cannot, for various reasons, now appear within the present year, 

 I have considered it better to issue the two volumes of the narrative 



separately. 



JOHN MURRAY. 



