352 Proceedings of the Royal Physical Society. 



itself in such spots ? In the New College Museum is a large 

 lump of rock crystal, on which the faces of the six-sided 

 pyramid are covered with a layer of iron oxide, lying wholly 

 on the surface, in the form of rough amorphous particles, and 

 destitute of this glaze. 



As I have been unable to find any published description 

 of this variety of amethyst, and as it presents some features 

 of considerable interest, I have thought it not unworthy the 

 attention of the Society. The plate is an attempt to re- 

 produce, in a rough way, the colours and the forms of some 

 of the spots shown in the section, exhibited to the Society 

 under the microscope. 



XI. On the Habits of the Water Vole (Arvicola amphibia). 

 By Professor Duns, D.D., President. 



(Read 21st April 1880.) 



The water vole is weU known under the name of the 

 water rat in most parts of Scotland. Yet, up to a com- 

 paratively recent date, much uncertainty prevailed both as 

 to its true zoological place and its habits. Its structural 

 relations may now be held fixed, but something still remains 

 to be put on record as to its habits. Bell (" British Quadru- 

 peds," p. 322) has shown good reasons for placing the water 

 vole nearer the beavers {Castoridce) than the mice (Muridce)^ 

 but it is doubtful if he has made out a case for the rejection 

 of the family designation Arvicolidm. The erroneous notion 

 that it feeds on small fishes, and even on the young of water 

 birds is still popular. This no doubt arises from its being 

 mistaken for the brown or Norway rat (Mus decumanus), 

 which takes readily to the water, and is destructive to duck- 

 lings. The water vole is a vegetable feeder, its food being 

 commonly the succulent stems and roots of aquatic plants. 

 It is thus to be regretted that Owen ("British Fossil Mam- 

 mals and Birds," p. 204) should seem to countenance the 

 notion that it feeds on animal substances. Eeferring to 

 traces of its presence in some of the British bone caves, he 

 says, '• remains of the Arvicola amphibia (lower jaws) were 



