Vol. 57.] ALTERED KOCKS FROM NEAR BASTOGNE. 65 



They are sometimes imperfect, and cr3'stallized against a patch of 

 ottr elite. 



The interior of the nodule consists of the same minerals with 

 s6me small sharp-edged crystals, probably white mica, some of 

 mineral No. 17 (see p. 61), small epidote, and patches of haematite 

 or limonite sometimes embedded in the ottrelite. In a squeezed 

 part, the sheaves of ottrelite grow across the planes of schistosity. 



This garnetiferous nodule appears isolated ; but about 2 feet 

 away, an irregular step left in quarrying shows altered rock, which 

 may have been previously a prolongation of the ' nodule.' The 

 mass is a compact greyish grit (with silvery mica along pressure- 

 2)lanes) forming indurated, dark, somewhat speckled bands above 

 and below ; while the central portion (about 1 foot thick) is more 

 altered, crowded with the supposed ottrelite, and similar to the 

 rock last described. 



Thin slices of the upper and lower bands are crowded with 

 minute greenish films and carbonaceous dust, and contain ilmenite 

 or haematite, with occasionally a minute flake of biotite. This 

 opacite is especially abundant along certain blacker layers. The 

 altered central band contains much carbon, crystals of iron-oxide, 

 sheaves of ottrelite, and small crystals of white mica which termi- 

 nate irregularly and fit on to adjacent grains, and thus evidently 

 are of secondary origin ; garnets, however, are absent. 



The cutting along the road extends for 100 yards or more, and 

 exhibits grits, often banded and very fine-grained, containing some- 

 times (in various specimens) filmy chloritic patches, iron-oxide, 

 white mica, possible scapolite, and a little biotite. The ground- 

 mass occasionally forms a clear recrystallized mosaic containing 

 rounded grains of corundum (?), and sometimes lath-shaped crystals 

 of mineral No. 17 or possibly a carbonate, which in one slice have 

 grown across the cleavage of included wedges of slate. 



In the quarries along the line to Gouvy, the strike of the rocks 

 is roughly parallel to the railway. The rock is a greyish compact 

 grit or an imperfect slate, developing structure-planes only in 

 weathering. On examination with the microscope it is seen to 

 have similar characters to that by the Longwilly road. The general 

 dip is about 20° north-westward or west-no ith- westward. 



Towards the south, above a slope of debris, is a boss somewhat 

 trapezoidal in shape, partly isolated by quarrying (fig. 4, p. 66), its 

 stratification dipping gently south-eastward. Here the mineral 

 changes are mainly restricted to a band roughly about 1 foot thick, 

 while the adjoining layers are hardly more than indurated and of 

 flinty appearance, with a greyish mudstone beyond, which at one 

 part below is jointed into small rhomboids. In the hard bands, 

 nearly vertical joints together with the almost horizontal bedding- 

 planes form cuboidal, or, in the upper part, imperfectly spheroidal 

 blocks which weather externally into platy flakes. 



Taking a section across the layers from above downward, one 

 finds : — A fine-grained quartz-felspar grit crowded with microliths, 



Q. J. G. S. No. 225. F 



