180 



district. There can be little doubt, from its mode of occurrence 

 in each case, that this mineral represents a secondary product 

 resulting from the decomposition of other ores of zinc, and the 

 rearrangement of the material in another compound. The Rowtin 

 Gill specimens are generally of a most beautiful blue tint, due, it 

 is said, to the presence of blue carbonate of copper. It is the 

 presence of this mineral that has earned for the Rowtin Gill variety 

 of Hemimorphite the name of Cupreous Silicate of Zinc. 



Chrysocolla, the amorphous form of Hydrous Copper monosili- 

 cate, is another mineral occurring in the Caldbeck Fells. Like the 

 mineral last-named it occurs exclusively in connection with the fault- 

 breccia, or rider, of the mineral veins ; and it is also in like manner 

 probably a secondary product resulting from the decomposi';i"n of 

 other ores. The Caldbeck Fell Chrysocolla usually occurs in the 

 form of resinous, or sub-vitreous, masses filling the interstices in 

 the vein-stuff, but sometimes it occurs in the form of small 

 encrusting spheroids grouped together on the faces of the vein 

 stuff in such a manner as to remind one of cauliflower heads rather 

 than of anything else. The mineral varies in colour from a clear 

 whitish green to a beautiful turquoise. Chrysocolla occurs at 

 several other localities than Rowtin Gill. I have seen it at the 

 old mines in the Glenderattera; and Mr. Bryce M. Wright mentions 

 Newlands, besides one or two other localities in the neighbourhood 

 of Carrick. 



Another series of silicates is formed by the species wherein 

 monoxides and sesquioxides are associated in the same mineral. 

 The first of these in our list is Idocrase, or Vesuvianite. It is 

 a fact of some interest that, although Idocrase is one of the best 

 known minerals formed in connection with the products of modern 

 volcanoes, yet the whole of the enormous accumulation of volcanic 

 material that forms our Lake District mountains has, so far, not 

 yielded even a trace of this mineral in the form of an original 

 constituent of the rock. In the only locality where its existence 

 has yet been made known, Wastdale Head, near the Shap Granite 

 Quarries, it occurs, it is true, in a group of rocks that are partly of 



