^0^' 57'] ALTERED EOCKS EEOM NEAR EASTOGNE. 59 



of * the proximity of a granite.' ^ I examined from this place many 

 specimens, among which I could trace under the microscope stages 

 of increased alteration. In two adjacent quarries, I found veins of 

 quartz, felspar, and mica. If these are not connected with a 

 granite but are only mineral veins, their occurrence among the 

 fine-grained mudstones is at least singular. 



Specimens of the sedimentary rocks (taken at various distances 

 from the veins) are sometimes slightly spotted, but do not otherwise 

 suggest contact-alteration, although such effects may be masked 

 by the dusty decomposed condition of the material. The microscopic 

 constituents, however, are mostly recrystallized. Among the speci- 

 mens from one quarry,' I find : — Firstly : at about 16 feet from the 

 vein, a brown-stained argillite, slightly indurated in one band. The 

 groundmass, crowded with narrow plates of iron-oxide, is composed 

 mainly of matted micaceous flakes of uniformly small size (average 

 often '03 mm. in length), generally with an orientation. Occasionally 

 a prism of hornblende or tourmaline occurs. Secondly : at about 

 2 feet from the vein occurs an iron-stained mudstone with minute 

 dark spots. A thin slice shows rather large quartz-grains irregular 

 and agglutinated, large mica without orientation (often about "05 mm. 

 long), and, in a finer-grained band, minute garnets. Thirdly : at 

 about 1 foot from the vein comes a dark, strong, ferruginous grit, of 

 clear quartz, pale green chlorite (probably altered biotite) in larger 

 flakes, generally grouped (often '2 mm. in length), and numerous 

 minute garnets. The latter are partly rounded, and much cracked 

 within. Some iron-oxide and an occasional grain of (?) staurolite 

 occur. Thus the abundant development of minute 

 garnets and the coarser-grained crystallization are 

 found nearer to the vein. 



In a neighbouring quarry I observed, on my first visit, branching 

 veins resembling rotten granite, which, however, in 1899 were no 

 longer visible. Specimens taken from this pit are much weathered ; 

 but on examining thin slices under the microscope, it is seen that 

 the flakes transitional from biotite to chlorite (brown or greenish to 

 almost colourless) are very large and frequently in clusters. One 

 specimen (to which a fragment of a vein adheres) contains flakes 

 often "15 mm. long, embedded in a clear quartz-felspar mosaic in- 

 cluding some grains of (?) corundum. "With this, we may compare 

 two other specimens from a third quarry close at hand. One consists 

 of clear grains parted by thin micaceous strings, and contains some 

 iron-oxide and a few minute garnets. A second specimen, traversed 

 by three subparallel veins (about ^ inch broad), consists mainly of 

 minute mica-flakes at right angles to the veins, and contains abun- 

 dant minute garnets. All these facts at any rate show increasing 

 alteration such as granite produces, as one approaches the veins. 



^ E, Dupont, 'Sur I'Existence de Roches Macliferes dans le Terrain Devonien 

 Inferieur de I'Ardenne Beige ' Bull. Acad. Eoy, Belg. ser. 3, vol. ix (1885) 

 pp. 110-14, Andalusite was described also from veins in the Cambrian rocks 

 of Stavelot, from strata near Laifour (Cambrian), and from ejectamenta in the 

 agglomerates of the Eifel. 



