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smaller quantities it is met with also in the highly-altered tuffs of 

 Bala age that form the deep rock-cutting on the London and 

 North Western Railway at Shap summit. As disseminated crystals 

 of small size it seems to be pretty generally diffused through most 

 of the Older Palseozoic eruptive rocks of Cumberland and West- 

 morland. It has not, so far as I am at present aware, yet been 

 found in our district in connection with any other rocks than those 

 specified. 



The important group of the Felspars falls next to be noticed. 

 To describe the mode of occurrence and the locality of each 

 species would require many pages of description; and, seeing 

 that the subject can be treated in a manner adequate to its im- 

 portance only in such publications as the Memoirs of the Geological 

 Survey, I shall confine my remarks on the present occasion to little 

 more than a mere list of the species observed. As native products, 

 that is to say, as minerals that have originated in the rocks where 

 they occur, as distinguished from such as have been derived from 

 pre-existing crystalline rocks, all the Felspars we have belong to 

 to one or other of the eruptive rocks. They have either been 

 brought into their present position as crystals when the rocks that 

 contain them were in process of formation, or else owe their 

 existence to a rearrangement of constituents already in the rocks, 

 which rearrangement has been brought about through the agency 

 of the causes comprised under the general term metamorphism. 

 Under the first, may be included the crystals of Felspar floated to 

 the surface in the old lava flows, or that, in association with other 

 mineral matter, have been intruded amongst prior-formed rocks in 

 the form of dykes. The fine series of porphyrite lavas of Bala age 

 at Rake Brow, Melmerby ; (which have been well represented by 

 specimens publicly exhibited in the Geological Survey Rock 

 Collection since 1881 ;) or, again, the equivalent rocks of Berrier 

 Nittles, near Greystoke, well exemplify the mode of occurrence of 

 Felspar crystals in lavas. The relation of the same minerals to 

 granitic rocks, and to plutonic rocks in general, is well exhibited in 

 such granites as that of Shap, where crystals of Orthoclase, often 



