NOKTII-AVrST RKUION OF CIIAllNWOOD FOREST. 91 



with numerous (micaceous ?) films, giving bright colours with polar- 

 ized light. These arc accompanied by irregularly outlined patches of 

 a green mineral, now a mass of flakes, acting little on polarized 

 light, perhaps belonging to the chlorite group : tliey are scattered in 

 a groundmass of felted and slightly foliated structure, composed 

 chiefly of brown earthy material and filmy viridite. 



If this rock had a fragmental origin, the materials must have been 

 volcanic, and the felspar and pyroxene chiefly clastic, but it bears 

 some resemblance to the rock of a dyke which occurs at no g'reat 

 distance in the bed of the neighbouring stream. This, if much 

 crushed and subjected to more micro-mineralogical change, might, 

 we think, present a very similar appearance. We have also compared 

 the rock with an undoubted slate-band which occurs at a distance 

 of a few feet to the south. The latter has a very difterent structure. 

 It consists of tiny fragments of clear quartz more or less angular, 

 felspar (?), mica, and iron-oxide, embedded in an earthy granular 

 matrix, stained more or less with ferrite and a little viridite. Some 

 ciilorite which occurs here and there in streaky patches is authi- 

 genous, but the white mica, at any rate, is allothigenous. In 

 short, the rock is like many very old slates, and, according to 

 Professor Bonney, resembles the workable slate of Groby Quarry 

 more closely than any other one in his collection from Charnwood 

 Forest. 



From the above considerations, it seems probable that we were 

 wrong in attributing the peculiarity of the " spotted slate " to 

 contact-metamorphism, and that it is more likely to be a dyke, 

 which has been exceptionally crushed and subsequently altered; 

 but it is impossible, with our present knowledge, to speak more 

 positively. 



7. The Igneous Junctions. — AVe described, in 1877 *, some sections 

 in Steward's Hay Wood, as proving the intrusive character of the 

 syenite. We have nothing of moment to alter in our description, 

 though it would be easy to add to the minor details ; but it must be 

 admitted that the supposed altered slate presents some resemblances 

 to the rock at the Stable Quarry, which we are now inclined to 

 consider an altered dyke, and its structure cannot be exactly 

 compared with that exhibited by any other case of contact-meta- 

 morphism which we have examined in other districts. Unfortunately, 

 we have had very few opportunities of studying the efiects of 

 intrusive rocks on a tine-grained ash, such as we supposed this to have 

 been, so that the apparent anomaly might disappear under more 

 favourable circumstances. Certainly, if the supposed altered slate 

 be a crushed dyke which has undergone much mineral change — the 

 only alternative, — there are some serious difficulties in the micro- 

 scopic structure and in the relations of the two rocks which call for 

 explanation. However, though we do not abandon our former view, 

 we think it right to say that it now presents difficulties which at 

 that time we did not feel. 



* Quart. Journ. Geol. Soc. vol. xxxiii. p. 78B. 



