PRE CARBONIFEROUS ROCKS OF CHARNWOOD FOREST. 203 



•013 inch long, others glassy ; ilmenite appears to be present as 

 well as magnetite. 



As stated in Part I. (p. 784), there are stratigraphic reasons for 

 thinking these two rocks nearly on the same horizon, and the 

 microscopic examination is not unfavourable to this correlation. 



MarTcfield Breccia by Copt-Oalc Road (p. 770). — Quartz grains are 

 rare in this, and broken felspar crystals less common than usual. 

 Some fragments of an altered slaty rock with lapilli of slaggy, 

 trachytic, and andesitic rock, generally minutely crystalline, and so 

 somewhat more difficult to distinguish than usual ; still some frag- 

 ments of the last cannot be mistaken. 



Breccia from Old- John Hill (p. 764). — Ground-mass in parts very 

 streaky ; broken felspar crystals here also less common than usual, 

 the majority plagioclase. Though this breccia contains huge frag- 

 ments of slate, most of the smaller are lapilli, and these are mainly 

 andesitic. 



Breccia from Ulverscroft Mill (p. 767). — As in the last, felspar 

 crystals are not very abundant ; a small number of angular and sub- 

 angular quartz grains ; lapilli of andesite very abundant, some also 

 trachytic, and a few perhaps are altered slate. 



As stated in Part I. (p. 784) there is reason to think these three 

 rocks about the same horizon. The microscopic examination, espe- 

 cially in the case of the first and second, is decidedly favourable to 

 the correlation. The rock of the spinney north of Old John described 

 above seems also very similar to them. Its position on the map 

 shows it to be probably intermediate between these and the rocks 

 described below, so that we may venture to include it also in 

 horizon 2. 



Timberwood Hill (p. 772). — The ground-mass is variable and 

 streaky ; there are the usual felspar crystals and occasional quartz 

 grains ; undoubted lapilli are rare ; one rather large fragment is 

 more like a clastic mass of small felspar crystals (i. e. a fragment of 

 an ash) than a true igneous rock. One fragment of quartz appears 

 to have split up into several pieces, between which the ground-mass 

 has made its way. 



Green Mill, Woodhouse (p. 766).-— Rather similar to the last, but 

 there is more subangular quartz, and the lapilli are more distinctly 

 marked, mostly not definitely andesitic. A large pinkish fragment, 

 included in the slide, shows the trachytic structure. 



Barnby Wood (p. 771). — The lapilli are still more distinctly marked 

 than in the last, and of the same character. 



Agglomerate under Slate near Cottages east of Monastery (p. 776). 

 — Felspars as usual ; lapilli rather numerous, some certainly ande- 

 sitic, one, besides plagioclase, showing a little hornblende, crystals 

 black-bordered*; quartz grains rather numerous; some ilmenite of 

 fair size, and viridite as usual. 



Coarse Agglomerate, Kite Hill (p. 775). — Felspar a good deal de- 



* Said by Zirkel (Report of Geol. Expl. of 40th Par. U.SA. vol. vi. p. 1)1) to 

 be very characteristic of the hornblendes of andesites and trachytes. Doubting 

 whether the black mineral is magnetite, he calls it provisionally opacite. 



r 2 



