502 



ME. P. HUXLEY ON THE EOCKS 



Silica = 44'76. Alumina = 16-60. Oxide of Iron = 8'43. Oxide 

 of Manganese = 0*20. Lime = 9-92. Magnesia = 8-56. Loss on 

 Ignition = 2*68. Alkalies and Loss = 8*85. 



No. 24. Swinyard's Hill. North side of highest point of ridge. — A 

 remarkably coarsely-crystalline rock composed of flesh-red felspar, 

 dark green hornblende, and quartz. This and No. 22 are perhaps 

 the most coarsely crystalline rocks in the whole of the Malvern 

 Hange. 



Under the microscope by ordinary transmitted light the horn- 

 blende appears of a greenish-brown colour, and some minute opaque 

 brown flecks, seemingly of limonite, may here and there be seen in it. 

 The felspar-crystals are mostly very large and exhibit no definite 

 crystalline form, their boundaries being extremely irregular. Some 

 of them are tolerably fresh, others considerably altered. One 

 measurement gave an extinction-angle of about 5°, another, but not 

 a trustworthy one, about 12°. They are probably microcline. The 

 quartz contains fluid-lacunae with bubbles. 



The rock is coarse hornblendic granite or quartz-syenite. 



No. 25. Swinyard's Hill, North side of highest point. — A rather 

 fine-grained, crystalline, diori tic-looking rock, apparently composed 

 of dark green hornblende and a pale grey or pinkish-grey felspar. 



Under the microscope the hornblende appears to be the principal 

 constituent (PI. XX. fig. 10). It is of a brownish-green colour when 

 viewed by transmitted light. Its pleochroism is strong, a=pale 

 brownish yellow, b= coffee-brown, c= greenish brown. 



Where moderately fresh, the extinction-angles of the felspars 

 indicate that they may be in some cases andesine, in others labra- 

 dorite ; but for the most part the felspars are greatly decomposed, 

 and no safe deductions can be formed concerning them, except that 

 they are triclinic. They appear, in most cases, to be replaced by 

 natrolite. Quartz, containing minute fluid-lacunae, is of common 

 occurrence in the section ; but the grains are small, and it forms a 

 comparatively insignificant proportion of the rock, which must be 

 regarded as a diorite. 



No. 26. Swinyard's Hill, just South of the summit. — A very dis- 

 tinctly foliated crystalline rock, the bands being alternately flesh-red 

 (or a finely crystalline admixture of flesh-red and greyish-white 

 minerals) and dark green, the constituent of the dark green bands 

 being probably hornblende. Under a pocket-lens a few minute 

 scales of silvery-looking mica are visible. The foliation reminds 

 one somewhat of that of the Schorlschiefer of Auersberg in Saxony ; 

 but in the latter rock the dark bands are intensely black instead of 

 dusky green. 



Under the microscope, quartz, magnesian mica, and, apparently, 

 some muscovite and triclinic felspars, especially microcline, are 

 seen to be the principal constituents of the rock. The cleavage- 

 planes in the mica have a general tendency to follow the foliation, 

 which in reality is due to this mineral. The quartz shows streams 

 of fluid -lacunas, which in nearly all cases run in a direction more 



