PBECABBONIFEROITS KOCKS OF CHARNWOOD FOEEST. 207 



pact purplish rock with whitish felspar crystals, the other a light 

 greyish red with pale green spots. A rock much resembling the 

 former occurs in the middle part of Bardon-Hill Quarry, and one 

 resembling the latter is common in the upper breccias of the same 

 place. 



(A) Purple Porphyritic Bock. — The following specimens of this 

 rock have been examined : — 



Ratchet Hill (p. 777). — With transmitted light the ground-mass 

 appears a tolerably clear glass full of minute black granules and 

 trichites ; there are occasionally small spaces clear of the granules, 

 like ill-defined felspar crystals, larger microliths of magnetite, larger 

 felspar crystals and grains of quartz, with a little epidote, and occa- 

 sionally viridite. With crossed Nicols most of the ground-mass 

 remains dark, but is crowded with small clear specks and long 

 narrow felspar crystals. The larger felspar crystals show both 

 orthoclase and plagioclase fairly well preserved ; some have a rather 

 broken outline, others a sharp linear boundary ; one or two quartz 

 grains show an approach to a crystalline form ; microliths and small 

 portions of ground-mass are occasionally included. A fragment 

 analyzed under the superintendence of Prof. Liveing gave, according 

 to one observer, Si0 2 =77*6 ; according to another, =77*9. 



Fragment from south of Peldar Tor (p. 775). — This rock has a 

 general resemblance to the last, except that the microliths are rather 

 more definitely aggregated, giving the slide a more granulated 

 structure. With crossed Nicols, however, many of the granules dis- 

 appear, and the rock resembles the last, except that minute acicular 

 felspar is more distinct ; several of the granules prove, by rotating 

 the prisms, to be minute spherulites. The same minerals are pre- 

 sent porphyritically as in the last, but they are not quite so 

 numerous. 



Breccia, Bardon Hill, Upper Quarry. — This rock so closely re- 

 sembles the last that a detailed description is unnecessary; the 

 larger felspar crystals, however, are decidedly more numerous, and 

 there is little or no free quartz, but more viridite and epidote. Its 

 structure seems to justify the correlation suggested in Part I. 

 (p. 782). 



Though the microscopic structure of the above rocks differs a little 

 from that of any recent igneous rock which we have hitherto seen, it 

 corresponds rather closely with that of both some quartz-trachytes 

 and some quartz-andesites from Hungary, so that they are doubtless 

 either rhyolites or belong to that large class of trachytes intermediate 

 between typical rhyolites and dacites. They correspond very closely 

 in the structure of the ground-mass with some of the devitrified 

 pitchs tones from the Wrekin. 



(B) Pinkish Felsitic Fragments in Breccias. — The following speci- 

 mens of this rock have been examined : — 



From Middle Exposure, High Towers (p. 774). — Ground-mass of 

 this slide seems to be a glass full of granular earthy dust. Crossing 

 tho Nicols shows the glass to be partly devitrified, with many bright 

 microliths in the dust, probably epidote, which is also abundant in 



