SURROUNDING THE LAND's-END MASS OF GRANITE. 409 



almost exclusively of brown tourmaline (dark shade in figure), 

 together with good examples of its micaceous or chloritic pseudo- 

 morphs ; and the intervening layers are composed of finely granular 

 quartz, sometimes clear and colourless, but more frequently stained 

 by a brown colouring matter, also disposed in parallel bands. We 

 have here, therefore, an example of the conversion of a clay-slate 

 into a somewhat micaceous tourmaline-schist. Another specimen, 

 also taken close to the granite, and within twenty yards from the 

 one just described, is a still more characteristic example of a tour- 

 maline-schist ; it consists wholly of folia of crystalline granular 

 tourmaline alternating with others of quartz, as seen in PI. XXIII. 

 fig. 3. The entire section is drawn twice the natural size, and 

 represents accurately the relative proportions of the two minerals. 

 The tourmaline does not occur in distinct crystals, but appears to 

 have run in among the grains of quartz, and to be moulded on to 

 them, as shown in fig. 4, which is a small portion of the same sec- 

 tion magnified 50 times. 



Mica-schist. — In the same locality, and at a distance of a few yards 

 only, a different bed of slate has been converted into mica-schist. 



The mica is a reddish-brown lepidolite, the crystals of which occa- 

 sionally contain laminae of a pale green colour ; a little schorl also 

 occurs here and there along the line of junction ; and in one slice 

 there are three small veins of well-crystallized tourmaline showing 

 the prisms arranged nearly at right angles to the sides. 



In a very fine-grained compact schist, also in contact with the 

 granite, the mass of the rock is crowded with innumerable minute 

 scales of lepidolite arranged in undulating lines interspersed with 

 narrow stripes of clear quartz. 



The junction of the two rocks is here very sharp and well defined. 



A section of the fine-grained schist, at about 15 feet from the 

 granite, exhibits a most remarkable arrangement of both quartz and 

 mica, as shown in Plate XXIII. fig. 5. The general appearance is 

 that of an irregular foliation produced by the linear grouping of nume- 

 rous red spots, each surrounded by a clear ring, and alternating with 

 narrow bands of red mica and strings of quartz. In the figure, the 

 clear spaces are quartz containing either extremely minute specks of 

 mica, or none whatever ; the granular parts consist of numerous 

 larger flakes, thickly crowded together, with small grains of mag- 

 netite disseminated here and there among them. In this case the 

 two constituents are not merely foliated in the usual way, but have 

 also undergone a further process of segregation into spheroidal and 

 elliptical nodules. This structure is well brought out in polarized 

 light ; for the clear crystalline quartz forming the oval rings then 

 exhibits colours differing from that of the surrounding parts, and 

 the nodules thus appear to be distinctly separated from them. 

 Concurrently with this process of rearrangement and partial crys- 

 tallization of the silica, some of the flakes of mica became crowded 

 together in clusters towards the centre, while others were at the 

 same time pressed outwards so as to occupy the angular spaces and 

 lines between the numerous adjacent nodules. Moreover all the 



