308 



small fibres, scales or granules." This substance the author designates 

 micro-felsite or micro-felsitic base. It occurs intimately interwoven with 

 micro-crystalline and crypto-crystalline aggregates. He regards it as a 

 definite chemical compound allied to felspar so far as the relations of the 

 alkalies and alumina are concerned, but containing a higher percentage of 

 silica. This substance, according to the author referred to, forms some of 

 the spherulitic aggregations so characteristic of many felsites and liparites. 

 When the fibres and scales are irregularly arranged the substance appears 

 isotropic ; when they assume parallelism, as in the case of the spherulitic 

 aggregations, they exhibit weak double-refraction. From what has been 

 stated above it appears that felsite is a macroscopic term used to include 

 substances which present very different microscopic characters. Some 

 felsites may be resolved into micro-crystalline aggregates of definitely 

 recognizable minerals (quartz and felspar or mica), others appear crypto- 

 crystalline, and others again are isotropic, but without that entire absence 

 of structure which distinguishes a glass. In addition to the above we find 

 felsites which break up under crossed nicols into aggregates O f double 



-I- OO O 



refracting grains or patches, often of extreme irregularity, but of consider- 

 able size. The different varieties of felsite above referred to are intimately 

 related to each other, and often coexist in the same rock. Flecks and specks 

 of black, red and green substances are very common in felsitic matter 

 VOGELSANG introduced the terms opacite, ferrite and viridite for these 

 substances. 



Spherulitic structures are very common in the trachytic rocks of acid 

 composition. The larger structures are often complex^ 1 ) in character and 

 will not be referred to at length in what follows. 



VOGELSANG separated spherulitic (spherical) bodies into five groups. 

 I. Cumulites. These consist of more or less spherical aggregations of 



globulites without radial structure. 

 II. Globospkerites. Aggregations of globulites or small cunmlites with 



radial structure. 



III. Bdonosplierites. These include aggregates with radial or concentric 

 structures in which the elements are definitely recognizable 

 crystals. 

 IV. Felsospkerites. These include more or less spherical bodies not 



definitely recognizable as belonging to any of the other classes. 

 V. Qra/no&pheritee. Spherical aggregates of definitely recognizable 



crystalline grains without radial or concentric structure. 

 The belonospherites of VOGELSANG are represented in the present group 

 of rocks by more or less spherical aggregations of quartz and felspar the 

 pseudo-spherulites of ROSENBUSCH. The outlines of these aggregates are 

 generally ill-defined. They are well-developed in certain portions of the 

 Armboth dyke and in the granophyre of Carrock Fell. The felsospherites of 

 VOGELSANG include many spherical bodies which present very different 

 appearances under the microscope. The relations of these different bodies to 



(1) See DELESSE, Recherclies sur les roohes globuleuses. Son. Geol. '.hid. Se. T. IV". Mom. 

 Xo. o. 



