396 NOTES ON THE LIZARD ROCKS. 



Porthallow Beach. {Pumice Stone.) 

 I have occasionally found pumice stone on this beach, 

 associated with gabbro, gneiss, serpentine, and tufa, though not 

 now a floating article. The infiltration of iron into the pores gives 

 to it the colour of jasper ; the weathered parts reveal its original 

 form after bleaching out the iron, the remaining portions 

 show sufficient vesicular structure to identify it as being an 

 ancient pumice stone. 



Obsidian from Penvose. 



Here an abundance of this rock is found in situ, with H 6 5, 

 specific gr. 2*284. It is banded, possesses a fluxine structure, and 

 contains many microliths and dendritic formations, fragments 

 of felspar and other kindred minerals ; some of the glassy bands 

 are more advanced in devitrification than others ; magnetism 

 very faint. 



Native Iron from the Lizard District. 

 Fig. 16, plate D. 

 Iron in one form or another is very abundant, and is supposed 

 to be the principal element of this planet ; in its native state it 

 is very rare ; it has been found in disseminated grains in basalt 

 and kindred rocks, and also in large masses in Greenland, where 

 probably it was derived from the disintegrated basalts of that 

 region, having been found associated with them. It so closely 

 corresponds with meteoric iron as to cause in the minds of some 

 a doubt of its telluric origin. It has also been found in the 

 Western Islands of Scotland and N.E. of Ireland in similar 

 rocks, viz : tertiary lavas and basalts, and now, for the first time 

 I believe, I find it in England, in small dykes that traverse the 

 gabbros and serpentines of the Lizard district. 



Native iron is reported by Dr. Johnston-Leves, to have been 

 found in the apex of Vesuvias in April, 1888. 



In preparing some slides from the small dyke at Dean Point, 

 iron was observed that did not correspond with magnetite in 

 general. When examined under the microscope with reflected 

 light, it was found to contain a bright central core surrounded 

 with a dark margin. Tested for metallic iron with sulphate of 

 copper, each trial was not alike successful. A sample from a 

 similar dyke near Coverack, when bruised, produced much larger 



