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 pipevno, and which I 

 have frequently seen exhibited in rocks from Iceland to Sicily. 



H. J. Johnston-Lavis. 



