^ol- 57'] ALTEEED EOCKS EEOM NEAE BASTOGNE. 61 



planes and often between the laths.^ The characteristics on the whole agree 

 best with ottrelite, by which name it is hereafter designated. ^ The 

 hornblende in the slides is usually green, shows distinct pleochroism from green 

 to pale straw, and gives bright colours with crossed nicols ; it is sometimes 

 intercrystallized with the mineral described above as ' ottrelite.' 



(16) Grains which show with crossed nicols the rich colours or bluish tints 

 usual in epidote. 



(17) Small grains, colourless, with high refraction, showing with crossed 

 nicols a drab colour or pale pink and green. They have no marked cleavage, 

 but sometimes a parallel twinning, are usually irregular in outline, with a 

 tendency to a wedge-shape or scalenohedron, are undoubtedly secondary, and 

 have even formed an irregular border along certain faces on one or two garnets. 

 I have failed to identify this mineral.^ 



The next two minerals occur in a few cases in rock adjacent to 

 the nodules : — 



(18) Grains, colourless, not highly refractive, with bright polarization- 

 colours, having one marked cleavage, and extinguishing straight ; these may be 

 scapolite. 



(19) Grains (some rounded), colourless, crossed by two cleavages, highly 

 refractive, showing often low interference-colours, extinguishing parallel to the 

 long axis of the grain. I incline to identify this mineral as probably corundum, 

 occurring often in what resemble fragmental grains. 



The examples of garnetiferous and hornblendic rock to be 

 described are from near Bastogne. Korth or north-east of that 

 town, a rounded ridge formed of a flattened anticlinal has been 

 cut, by both the road to Long willy and the railway to Kautenbach, 

 and quarried extensively for ballast along the railway to Gouvy. 

 The quarries at the last-named locality have been probably cut 

 back since Prof. Gosselet made a drawing of one nodular mass,"^ but 

 I found in them two examples of the garnetiferous or hornblendic 

 rock ; and by the road to Longwilly, three. 



1 will begin by describing one of the last-named instances. This 

 occurs in a craglet about 5 or 6 feet high, which consists of compact 

 sedimentary rock with almost horizontal greyish bands and blackish 



^ I presume this mineral to be that figured by Prof. Renard in the ' Taunusian 

 garnetiferous rocks' Bull. Mus. Eoy. Hist. Nat. Belg. vol. i (1882) pi. i, fig. 2, and 

 included by him in the variety of amphibole. In his earlier paper, Ann. Soc. 

 Geol. Belg. vol. vi (1879) pp. 55, 65-67, he gives a full description of it and 

 reasons for referring it to ottrelite rather than hornblende ; but in 1882 (Bull. 

 Mus. Roy. Hist, Nat. Belg. vol. i, pp. 19-22) he withdraws the previous 

 identification, and accepts Dumont's reference to actinolite, remarking, however, 

 that the large amount of alumina present in it is a difficulty. 



2 The mineral agrees with the ottrelite of Dana, and differs from chloritoid 

 in being feebly or not at all pleochroic. But the distinction of closely allied 

 species is not clear : — Prof. Iddings places chloritoid under the ottrelite-group ; 

 M. Michel-Levy and Dana (in an earlier text-book) place ottrelite under the 

 chloritoid-group ; Dana (in his ' System of Mineralogy,' 6th ed. 1892, following 

 Tschermak) describes chloritoid and ottrelite as two species of the. clintonite- 

 group, but, speaking of the chloritoid in schists or phyllites, occurring in fan- 

 shaped or sheaf- like forms, says that ' most of what has been called ottrelite 

 probably belongs here ' {pjp. cit. p. 642) ; Mr. G. Barrow, ' On the Occui^rence 

 of Chloritoid in Kincardineshire ' Quart. Journ. Geol. Soc. vol. liv (1898) p. 154, 



suggests 'that chloritoid, ottrelite, etc have really the same composition, 



if we could only obtain pure material to work upon.' 



^ It has been suggested to me that this might be sphene. We ha:l considered 

 the possibility, but were not very satisfied with that identification. 

 * ' L'Ardenne ' (1888) p. 769 & fig. 208. 



