666 PROF. I.G. BONNEY ON THE MICROSCOPIC 
and hornblende, both rather decomposed, with a little iron peroxide 
and chlorite. ‘The felspar is mainly plagioclastic ; but some crystals 
resemble orthoclase. It is possible that the hornblende may be of 
secondary origin ; but the rock can now only be defined as a diorite. 
It is not unlike one of the ‘“ traps” from Malvern in my collection. 
(D) The Quartzites—The first specimen, from ‘‘near the cottage on 
the Wrekin,” and thus from quite the lower part of the quartzite series, 
contains numerous rather angular fragments, some +" long, of a 
material like decomposed pumice. Microscopic examination shows 
that the rock consists of well-rounded quartz-grains and fragments 
of varying size, some rounded, but most rather angular, of a rather 
decomposed rhyolitic rock, doubtless that of the Wrekin. One frag- 
ment still exhibits perlitic structure. There is but little cementing 
material, and this appears to be quartz. The quartz-grains are 
pretty full of very minute enclosures, and bear a strong resemblance 
to those of the granitoid rock described above. 
There is a point of general interest in this rock worth noting, 
namely, that the quartz ‘‘ cement,” which is obviously of secondary 
formation, is often deposited so as to form one crystal with that in a 
grain (proved, of course, by their giving the same tint with crossing 
Nicols). The boundary of the grain, however, is clearly shown by 
the cessation of enclosures, from which this secondary quartz is 
remarkably free. 
The second specimen is from “ section 8.E. of Charlton Hill.” It 
consists of similar quartz in smaller grains, and finer fragments 
(often almost triturated and acting as cement) of a rock which 
appears to be rhyolite. The third specimen, ‘‘ W. of Rushton, N.W. 
of Wrekin,” is rather coarser than this ; of the presence of the rhyo- 
litic rock here, though in smaller grains than in the first, there can 
beno doubt: some of the quartz is very full of enclosures. Magnified 
about 70 diameters, they appear as dusky specks, about 200; some 
remain opaque, but most prove to be cavities of variable form, in the 
larger of which I sometimes detect very minute bubbles, but cannot 
distinguish any in the smaller. Some of the grains themselves 
- exhibit a compound structure, as if derived from an older quart- 
zite. 
(1) Hast Field, near Burcot.—A glassy-looking rock, with wavy 
irregular lines of opacite and ferrite, indicating a fluidal structure, 
and occasional well-preserved felspar crystals, with rather broken 
edges. Both orthoclase and plagioclase can be recognized ; with 
crossed Nicols a minute eryptocrystalline structure is visible, a con- 
siderable part of the slide being dark. The basis has once been 
glassy, and, so far as can be ascertained, a portion yet remains 
undeyitrified. The rock appears to an old rhyolite of the Wrekin 
type. 
(2) Burcot, Wrockwardine.—The microscopic structure of this 
rock comes rather near to that of no. 5, and it is not without hesita- 
tion that I place this among the sedimentary. The mineral compo- 
sition, however, is, I expect, not very different. Parts of it with 
crossed Nicols show a very similar structure; but the aspect of this 
