OP THE MALVERN" HILLS. 



497 



ing, on a cut surface, small reddish-brown and greyish-white 

 blotches on a dark bluish-grey ground. 



Hornblende, triclinic felspars, quartz, epidote, apatite, and a little 

 pyrites and chlorite appear, under the microscope, to be the principal 

 constituents of this rock. 



Some of the felspars, judging from their extinction-angles, are 

 labradorite, while others occasionally give an extinction -angle of 

 89°, and must consequently be referred to anorthite. The horn- 

 blende appears of a pale green colour by transmitted light ; it occurs 

 in irregularly bounded crystals which show the characteristic cleavage. 

 The epidote occurs in moderate-sized crystals and in small grains. 

 The quartz has segregated so as to form distinct bands, which 

 alternate with the very irregular bands of hornblende, epidote, &c, 

 through which more or less quartz is also disseminated. 



It is difficult to assign any precise origin to this rock ; it might 

 quite well have resulted from the degradation of syenitic rocks or 

 hornblendic gneiss. It may even be regarded as a fine-grained 

 hornblendic gneiss, and it is to the latter rock that I am inclined pro- 

 visionally to refer it. Its general appearance by ordinary transmitted 

 light under an amplification of 18 linear is shown in PL XX. fig. 7. 



No. 18. Herefordshire Beacon. Close to and on the west of the 

 Cave. — Rather coarsely crystalline dark greenish-grey rock resem- 

 bling basalt. 



Under the microscope the constituents are seen to be augite, 

 triclinic felspars, apatite, pyrites, and serpentine (PI. XX. fig. 8). 

 The crystals of augite are occasionally over -fa inch in length. The 

 characteristic, almost rectangularly-intersecting cleavages may be 

 seen in the basal sections. The crystals are intersected by strong 

 and very irregular fissures, frequently accompanied by peroxide 

 of iron, which communicates a rusty stain to the augite for 

 a slight distance bordering the cracks. Here and there minute 

 scales of specular iron may also be seen lying within the substance 

 of the augite. In sections parallel to 010 the measurements of the 

 extinction c : c vary but little from 38°. These augite-crystals 

 barely exhibit a trace of pleochroism. The felspars show by their 

 extinction-angles that some of them are labradorite, while others, 

 and those perhaps the more numerous, are anorthite. The latter 

 show, as a rule, less twin-lamellation than the labradorite, and the 

 extinction-angle measured in four or five sections is 37° and some- 

 times 38°. Pale green patches of serpentine are common in the rock 

 and probably result from the alteration of olivine. No distinct forms 

 which can be referred to crystals of olivine, however, are to be met 

 with in the preparation. The pyrites occur in very irregularly-shaped 

 patches often traversed by a labyrinth of channels and generally 

 very much cut up by branching cracks, which, when seen by reflected 

 light, appear to be filled with haematite, while the pyrites is very 

 frequently seen to be intimately associated with magnetite, the 

 latter mineral always enveloping the pyrites. Prom its mineral 

 constitution the rock appears to be related to eucrite. 



An analysis of a rock from the same locality, no doubt the same 



