274 Scientific Intelligence. 



The melanocratic rocks described are camptonites, kersantites, 

 vogesltes and monchiquitea of various types; together with 

 minettes, rich in soda and containing aegirite, and farrisite. 

 Farrisite is a new type, consisting of barkevikite, colorless 

 pyroxene, a little lepidomelane and traces of olivine, iron ore, 

 apatite, etc., mixed with a colorless tabular tetragonal mineral of 

 the scapolite group which plays the part of the feldspathoid and 

 makes up about 35 per cent of the rock. The structure is fine- 

 granular and megascopically the rock is deep chocolate-brown in 

 color and very compact. Another new type belonging to this 

 class is heumite y a dark-colored, compact hue-granular rock corn- 

 posed of barkevikite and biotite with alkali feldspars as chief 

 components and with smaller amounts of nephelite, sodalite and 

 cliopside. 



The leucocratic rocks are nephelite-porphyry \ tinguaile, sdlvs- 

 bergite, bostonite, foyaite (Brogger uses this term to designate 

 normal nephelite-syenites with trachytic structure while those 

 with hypidiomorphic granular structure he terms " ditroites") and 

 hedrumite. The last-named rock type is defined as the chemical 

 and mineralogical hypabyssal equivalent of pulaskite, possessing 

 trachytic structure and therefore composed chiefly of alkali feld- 

 spar and poor in nephelite. In addition syenitic aplites are 

 described under this group of alkaline type — the lestiwarites of 

 Rosenbusch. Of all these types chemical aualyses are given and 

 the mineral composition and systematic position are thoroughly 

 treated. 



In the concluding portion of the work the bearing of the facts 

 observed on theoretical petrology is discussed and it is shown 

 that these dike magmas are to be regarded as derived from the 

 laurdalite magma by differentiation, the melanocratic and leuco- 

 cratic types being complementary derivatives. Many questions 

 of general interest are handled including a masterly discussion of 

 the "kern" hypothesis of Rosenbusch which it is shown can be 

 only accepted in a modified form. The latter portion of the 

 memoir is indeed full of suggestions and will furnish material for 

 thought to all petrologists. l. v. p. 



4. Haddeckite, a neic variety of Muscovite ; by G. C. Hoff- 

 mann. (Communicated.) — This interesting variety of muscovite 

 was met with about half a mile from the town of Baddeck, 

 Victoria County, in the province of Nova Scotia, where it occurs, 

 in the form of minute isolated scales, small scaly aggregations, 

 and thin scaly layers, distributed through a highly plastic clay ; 

 which also contains a large proportion of fine crystalline, white, 

 pearly scales of kaolinite, some minute crystals of white quartz 

 and small particles of pyrite and calcite. 



The mineral has a fine copper-red color, a pearly luster, and 

 affords a tile-red streak. With water it forms a highly plastic 

 mass. Its specific gravity, at lob C, is 3-252. Before the 

 blow-pipe it fuses, at about 4*5, to a shiny black slag, which on 

 continued heating in the reducing flame becomes magnetic. It 



