OP THE MAEVEEX HUES. 



495 



irregular in form and appear to be bound together by a crvpto- 

 crystalline cementing material. The felspar appears to be orthoclase ; 

 the garnets are only to be recognized by their isotropy, while the 

 quartz contains numerous fluid lacunae, some of them with bubbles 

 which exhibit spontaneous movement when examined under a power 

 of about 800 linear. 



The rock is a granulite and, in common with rocks of this class, 

 is remarkably tough under the hammer. Portion of a thin section 

 as it appears between crossed nicols and magnified 55 linear is 

 shown in PI. XIX. fig. 8. 



No. 12. Worcestershire Beacon. North side near summit. — A 

 granitic-looking rock, coarsely crystalline and apparently composed 

 of quartz, pink felspar, and mica. 



Under the microscope the constituents are seen to be microcline, 

 quartz, biotite, and apatite. Here and there a little limonite and 

 specular iron occurs ; one or two small crystals of hornblende may 

 be seen, in which the angle c : c is exceptionally large, being over 

 30°. The pleochroism is somewhat distinct. The biotite, when 

 examined under a tolerably high power, is found to be spotted with 

 stains and patches of ferric oxide, and in some places scales of 

 specular iron are developed. In other cases spicular bodies which, 

 when magnified about 800 diameters, are seen to consist of strings 

 of globulites massed in small fasciculi appear dark and opaque 

 except towards their ends, where their component globulitic strings 

 are frayed out and the globulites are seen to be translucent. These 

 globulitic crystals, for as such they may be regarded, probably 

 represent an early stage in the development of some such mineral 

 as hornblende. Furthermore, they intersect at angles of 60° in 

 basal sections of the biotite, and evidently lie in the directions of 

 the three lines which form the percussion-figure of this mica. In 

 sections normal or oblique to the cleavage of the biotite they appear 

 merely as dark lines which follow the cleavage-planes. There is a 

 certain resemblance in this arrangement which recalls the well- 

 known crystals of specular iron in the Pennsbury mica, but the 

 latter have sharply defined boundaries. Crystals and scales of 

 specular iron also occur in the biotite of this Malvern rock, asso- 

 ciated and sometimes in contact with the globulitic crystallites 

 just described ; but here, too, the specular iron exhibits sharply 

 defined boundaries, and there is no doubt that whatever the globulitic 

 bodies may be, they represent the incipient development of some 

 mineral which retains any iron it may contain in the protoxide 

 state, since the globulites are either colourless or pale green : but, 

 since the surrounding biotite is of a green colour, it is difficult to 

 say what their colour would be by transmitted light, if isolated. By 

 reflected light the opaque portions of these crystallites, where the 

 globulites have become densely packed, appear of a pale green or 

 greenish white. A drawing of some of them, as seen by substage 

 illumination and magnified 850 linear, is given in PI. XXI. fig. 6. 



The rock is granite. Portion of the section magnified 18 linear 

 is shown in PI. XX. fig. 2. 



2l2 



