724 



MISS C. A. RAISIN" ON THE 



colourless microliths, somewhat dichroie, if I could trust my not 

 very clear observation ; they may possibly be a secondary acti- 

 nolite. In these micaceo-chloritic slides mica plates at parts form 

 level and continuous layers, at others they constitute bent or wavy 

 laminae. Occasionally there is an example of a breaking and 

 slipping of the layers at the folds, which I will indicate later, when 

 I speak of similar structures in other schists. 



3. Mica-Schist. — True mica-schists form the dark massive cliffs 

 which extend towards Bolt Head, with a kind of black-lead sheen, 

 and the paler, more silvery rock of the cliffs near the Start. In 

 the Bolt specimens I identified the constituents described by Pro- 

 fessor Bonney, and found one fragment showing good examples 

 of what I believe to be kyanite. The grains are visible without 

 magnifying, and, thus looked at, they are seen to be about T \ inch 

 in diameter, to be blackish in colour, and to have somewhat of a 

 prismatic form. Under the microscope the grains, some of them, 

 show clear kyanite-like cleavages, and in one is a good example of 

 twinning. Where this clear mineral occurs, it abruptly interrupts 



Pig. 2. — Crystal of Kyanite in Mica-Schist near Bolt Head. 

 (Enlarged 70 diameters.) 



The schist ccmsists mainly of chlorite, white mica, and " black mineral," and its 

 layers pass on through the kyanite. The kyanite shows one good cleavage, 

 with interrupted planes, and is twinned. 



the micaceous and chloritic layers ; but the ferro-carbonaceous 

 material (as I infer it to be from Professor Bonney's description) 

 seems to continue on in its own wavy laminae through the kyanite 

 (fig. 2). Here, therefore, where the grains are larger, they contain 

 more foreign deposit, some of them being almost full of the black 

 dust ; but its arrangement seems only explicable by supposing the 

 growth of the kyanite-grain in situ in the rock. The schist from 

 Start Point seems to have in it less of the black mineral, its mica- 



