on Qjiartz Rock. 271 



rhomboidal tables. In this respect it bears a considerable analogy 

 to the clay slates with w r hich it is so often associated. 



Among the varieties found in Ben Cloe T. remarked some others 

 worthy of notice, considering the novelty of this subject and the 

 necessity of describing every remarkable feature of a rock so long 

 overlooked or confounded with others. The most singular of these 

 is of a beautiful pink colour, equal to that of the well known rose 

 quartz, with the semi-transparency and fine grain of the most highly 

 refined sugar : it forms interesting specimens for collectors of mi- 

 nerals. I have mentioned it in describing Glen Tilt. Another is of 

 a dark brown colour, apparently from containing much carbonate of 

 iron, but when it is exposed to the weather the surface is bleached 

 to the depth of a quarter of an inch and becomes of a snowy 

 whiteness. A third is of an ochre yellow colour and loose texture, 

 and in hand specimens not to be distinguished from a common 

 secondary sandstone, while at the same time it contains distinct con- 

 cretions of crystallized carbonate of lime irregularly dispersed through 

 it. A variety equally resembling some of the secondary sandstones 

 which occur among the coal strata in the vicinity of Glasgow and 

 elsewhere, is found near Balahulish. It is distinguished by the fre- 

 quent alternation of black laminse, of which the cross fracture repre- 

 sents delicate lines, and it serves with others already enumerated to 

 confirm the strong affinity of the recent sandstones with quartz rock, 

 the sandstone of former ages. 



Among the various modifications of quartz rock which I have 

 observed in the different districts now described, a great many exhibit 

 the characters of the avanturine, the quartz avanturine of Brongniart. 

 I have frequently noticed the transition which takes place between 

 quartz rock and mica slate, a transition so gradual and so perfect 

 that it is often impossible to assign the limits of the two. The quartz 



2m 2 



