178 



mineral under notice occurs in crystals ranging up to about a 

 quarter of an inch in length. These crystals exhibit well-defined 

 faces of cleavage, which have a somewhat horny-looking texture, 

 and a sub-metallic lustre. In each case the Diallage is associated 

 with Oligoclase Felspar, and with more or less titaniferous iron. 



Hornblende, again, belongs to the same raineralogical group 

 as the species already enumerated ; but it differs from any of them 

 in its crystalline form, as well as in its angles of cleavage, and, to 

 some extent, also in its chemical composition. Hornblende in 

 Cumberland and Westmorland occurs almost exclusively as an 

 original constituent of the eruptive rocks of Older Paleozoic age ; 

 and it is found rarely or not at all as a product of metamorphism. 

 It forms an important constituent in the crystalline rocks of the 

 Buttermere and Ennerdale " Syenite " or Hornblendic Granite, 

 and of the Diorite of Carrick Fell, as well as of several other 

 crystalline eruptive rocks occurring in the two counties. The 

 more important of these will be found described in detail in Mr. 

 Ward's various papers on the Petrology of Cumberland and West- 

 morland.* 



Crystals of Hornblende rarely attain to any considerable dimen- 

 sions in the area under notice ; and indeed it has not been possible 

 to prove the existence of this mineral at all in the case of many 

 varieties of rocks, except by means of an examination of thin slices 

 of rock with the aid of the microscope. Detailed descriptions of 

 these observations will eventually appear in the official publications 

 of the Geological Survey ; where the subject will be treated in a 

 fuller manner than is possible here. 



AcTiNOLiTE, one of the fibrous sub-species of Hornblende, 

 occurs in a few locahties; generally in association with one or 

 other of the Older Palseozoic eruptive rocks. Near Melmerby it 

 is found in the form of narrow veins traversing an altered and 

 much-decomposed intrusive mass of "greenstone" — using that 

 term in its old, and very convenient, generic sense, as meaning a 

 crystalline eruptive rock containing one or other species of either 

 the Augite or the Hornblende group. The Actinolite at Melmerby 

 * A list of tliese is given in Number VII. of our Transactions. 



