162 



the lake. In the hills of Cabo Blanco, angular 

 masses of opake quartz, scarcely translucid on 

 the edges, and varying from gray to deep black, 

 are found amid the gneiss. It passes some- 

 times into hornstein, sometimes into kiesel- 

 schiefer (schistoid jasper). I do not think it 

 constitutes a vein. The waters of the lake* 

 decompose the gneiss by erosion in a very extra- 

 ordinary manner. I have found parts of it 

 porous, almost cellular, and split in the form of 

 cauliflowers, fixed on gneiss perfectly compact. 

 Perhaps the action ceases with the movement of 

 the waves, and the alternate contact of air and 

 water. 



The island of Chamberg is remarkable for it's 

 height. It is a rock of gneiss, with two summits 

 joined in the form of a saddle, and raised two hun- 

 dred feet above the surface of the water. The slope 

 of this rock is barren, and can scarcely support 

 a few plants of clusia with large white flowers. 

 But the view of the lake, and of the richly cul- 

 tivated neighbouring valleys, is admirable ; par- 

 ticularly after sunset, when thousands of aqua- 



* The water of the lake is not salt, as is asserted at Ca- 

 raccas. It may be drunk without having been filtered. Oiv 

 evaporation it leaves a very small residuum of carbonat of 

 lime, and perhaps a little nitrat of potash. It is even sur- 

 prising, that an inland lake should not be richer in alcaline 

 and earthy salts, acquired from the neighbouring soils* 

 HdUey. 'Phil. Trans, 1715, p. 295* 



