i893. STRUCTURE OF IGNEOUS ROCKS. 221 



In Ischia, on the east coast of the island, is a lava in which two 

 magmas seem to have issued and flowed together, almost reproducing 

 that kind of structure of earthenware, of mottled design, made by 

 working together different coloured clay. From that we pass to the 

 banded trachytes of Palmarola and the so-called felsites (because they 

 are old) of the neighbourhood of Dresden, or the liparites of Basiluzzo. 



The vitreous crust of some of the flackers, the peculiar conforma- 

 tion around foreign enclosures, the nature of these latter, and many 

 other points might be discussed as confirming this- explanation. At 

 any rate, I hope to have cleared up a knotty point in lithology by 

 showing that my theory of volcanic action is able to explain even an 

 intricate rock structure, such as that which I have called " pipernoid," 

 from its remarkably perfect illustration in the piperno, and which I 

 have frequently seen exhibited in rocks from Iceland to Sicily. 



H. J. Johnston-Lavis. 



