186 



Beryl, the Alumino-glucinum Silicate. So far as I know at 

 present, the claim of the Beryl to be counted as a mineral from 

 this locality rests on the identification of specimens now in the 

 Museum at Keswick. These specimens are from a vein traversing 

 the volcanic rocks at Walla Crag, on the east side of Derwentwater, 

 and are in the form of slender prisms about an inch and a quarter 

 in length, by an eighth of an inch in diameter, and varying in 

 colour from whitish grey to dark milk-blue. There is no reason 

 whatever why the Beryl should not be found here, as it has been 

 found in similar rocks in other parts of the kingdom. 



The Hydrous section of minerals belonging to the last series of 

 silicates come next, and includes the Zeolites and Chlorites. 

 This section will, doubtless, hereafter prove to contain many more 

 mineral species than present knowledge enables me to enumerate 

 here now. It is perhaps not unfair to previous observers to say 

 that a critical examination of the rocks of the Lake District has 

 only just been commenced, and that we .yet have much to learn 

 on this subject and others allied to it. 



Pectolite is occasionally found as a vein-mineral in some of 

 the fissures traversing the sheet of basalt intruded into the Carbon- 

 iferous rocks lying on the north-east side of the Pennine Fault. 

 This is the black rock so well-known under the name of the Whin 

 Sill.* Pectolite occurs in the form of close-set aggregations of 

 silky-looking acicular crystals of a light-grey colour, which extend 

 from side to side ot the vein, in the same way as Actinolite does. 

 Calcite occurs in association with it ; perhaps because limestones 

 at no very remote period, once covered the Whin where this 

 mineral occurs. 



One of the most important and most widely-diffused of the 

 hydrated silicates, at least in the Older Palseozoic rocks of Cum- 

 berland and Westmorland, is the mineral Chlorite. It is to the 

 presence of this mineral in a diffused state that the peculiar pale 

 grey-green colour of so many of our volcanic rocks is due. The 



* Whin, ill the North of England, means any rock hard enough to be em- 

 ployed as road-metal, and is by no means restricted to Easalt. Sill is used 

 as an equivalent texni for sti-atum. 



