276 



Christmas Island. 



by talus. The surface of this rock in contact with the limestone 

 seems to have been greatly altered before the latter was deposited. 

 In the centre of the mass the rock (No. 929) is light- grey, fine- 

 grained, and made up of a felt of small lath-shaped felspar crystals, 

 giving straight extinctions and showing flow structure round 

 vesicular cavities which themselves show a more or less linear 

 arrangement. There are some traces of a much altered ferro- 

 magnesian mineral between the meshes of the felspars. Professor 

 Judd has kindly had the specific gravity of this rock determined 

 for me ; it is 2-45. 



-SOO FT 



-■f^SO 



Figure 5. 



Sections shoaving the Structure of the Cliff at Flying Fish Cove. 



A. At middle of section B, Fig. 2. 



B. At right-hand end of section B, Fig. 2. 



For explanation of lettering see Fig. 2 (p. 272). 



A few chains farther north trachytic rock again appears, but 

 in this case under peculiar conditions. Here the trachyte forms 

 two or three large masses, apparently completely included in the 

 great bed of basalt which there immediately underlies the yellow 

 limestone. The trachyte is here much altered, and consists of 

 angular nodules separated by a brown powdery substance, apparently 

 produced by the decomposition of the rock along cracks. In one 

 place the basalt sends a finger-like process into the midst of one of 

 the trachytic masses, and in another it appears to have penetrated 

 the trachyte horizontally for some distance, so as to appear to be 

 interbedded with it. The whole structure seems to be the result 



