Q. A. Lebour— Notes on Staurolite. 103 



ever, not seen at this particular spot. In the immediate neigh- 

 bourhood of Coadry the junction between the mica-schist group and 

 the granitic mass is well seen and easily followed. It is shown 

 tolerably correctly in the " Carte Geologique du Finistere." 



At and near this junction the rock is true mica-schist, of a dark 

 greenish-grey colour, with spangles of mica of large size. In these 

 beds none but a few very small specimens of Staurolite were met 

 with, but these were all beautifully perfect, double, and crossed at 

 right-angles. A little further from the junction the crystals (still 

 perfect and crossed at right-angles) are to be found in great 

 abundance and of large size, some as much as 2 in. x 2 in., studding 

 the rock (which is here less micaceous and more quartzose) by 

 hundreds. A stream cuts through this portion of the series, and its 

 bed is naturally full of those large twin crystals, which are very 

 easily detached from their parent rock, and it is evidently here that 

 the " Pierres de croix " are found. The band in which these fine 

 specimens abound is about thirty or forty yards in breadth, and near 

 its inner margin (that furthest from the granite) there is a large pro- 

 portion of crystals, crossed in the manner of a St. Andrew's cross. 

 Beyond this band, in a very similar rock, but of a rather lighter 

 colour and more friable, the number of crystals of the latter kind is 

 much smaller, and with few exceptions the majority of the others, 

 although crossed at right-angles, are formed of unequal prisms, one 

 of them being in length smaller than the width of the other. This 

 is also the case with the diagonally-crossed crystals, though more 

 rarely. This last band of rock is about twice the breadth of the 

 preceding one, and is succeeded by a large area of less micaceous 

 clayey schists of a light yellow colour, sometimes hard enough to be 

 used for building purposes, sometimes crumbling like earth in the 

 hand. As we enter this region, the double crystals become rarer and 

 rarer, and soon die out altogether, giving place to single prisms of 

 all sizes, some reaching a length of from three to four inches. These 

 single crystals are much softer than the double ones, and, when found 

 in the more earthy parts of the schists, seem to form the nuclei of 

 clayey concretions, distinguishable chiefly by their colour, which is 

 of a darker tint than the rest of the rock. I was not able to ascer- 

 tain where this " single crystal " zone ends, either in the Coadry 

 district or at Lhomine, but about a mile from the junction with the 

 granite no traces of Staurolite ever rej)aid my search, although, in 

 several instances, brownish clayey nodular-looking patches were 

 seen very similar to those just mentioned.^ 



Without attaching any undue importance to the facts I have just 

 described, the connexion between them and those brought forward 

 by Fuchs appears to be sufficiently obvious. The gradual indica- 

 tions of metamorphism which he observed in the Pyrenees to be 

 accompanied by the formation of Andalusite and Chiastolite, are 

 apparently repeated to some extent in Brittany, with the substitution 

 of a mineral nearly allied to the two last-named ones in chemical 



1 All the specimens are when found in situ of a light rusty-brown colour, the black 

 colour of those bought at fairs being due to polishing with oil. 



