4 J. CLIFTON WARD ON THE GRANITIC, GRANITOID, AND 



of which the rock is composed standing out with sufficient distinctness ; 

 but in other parts the granular structure is more or less obscured by a 

 wavy and indistinct meshwork of greenish and brown matter, among 

 w T hich small mica particles are pretty generally diffused. 



The crystals of chiastolite are variously developed and are cut in 

 every direction, thus yielding many different forms (see figure), 

 the sections being longitudinal, transverse, or oblique to the principal 

 axis. They invariably contain small particles of carbon, grouped 

 mostly, and often exclusively, at the centre ; and associated with 

 these and also occurring in the base, are short black bars, probably 

 of pyrites. 



The crystal- sections have a narrow edging with a netted appear- 

 ance, which appears as a minute coloured mosaic in polarized light, 

 while under the same conditions the interior is either coloured or 

 dark in spaces separated from one another by minute canals. Some- 

 times, as in the case of the crystal the pointed end of which is seen 

 at the bottom of the figure, when the interior appears dark under 

 crossed prisms, the margins and canals stand out brightly illuminated. 

 In ordinary light the interior has a general light-brown tint between 

 the canals. 



In the figure it would almost seem as if the long crystal had been 

 broken and its parts severed by the formation of the central lozenge- 

 shaped one ; and it is curious to observe how markedly wavy the base 

 is at the upper end of one of the long fragments. There also occur 

 a few very minute scattered prisms of a mineral which may be anda- 

 lusite, showing mostly red and green colours in polarized light. 



2. Spotted Schist (Knotenschiefer). (Plate I. figs. 2, 3, & 4.) — 

 The chief points to be noted in the microscopic examination of this 

 rock are the great number of the rectangular spots and the crystalline 

 nature of the base. From fig. 2 an idea may be gathered of the 

 distribution of the spots, frequently much along the planes of cleavage, 

 which now become more or less distinct planes of foliation. Some- 

 times the spots are long and narrow ; but the more general form is 

 rectangular or oblong. When viewed with polarized light, most of 

 them distinctly exhibit shades of colour arranged in the form of a 

 cross, as shown in fig. 3 ; and there seems to be little doubt that the 

 spots are undeveloped chiastolite crystals. Particles of carbon (?) 

 frequently occur in connexion with them as well as in the base, as- 

 sociated with bars of pyrites. In some specimens the numerous 

 decomposing pyrite particles are very evident upon the weathered 

 outside as well as under the microscope. The base around these spots 

 is made up of very minute prisms, showing red and green colours 

 under polarized light, and frequently taking a flowing arrangement 

 (fig. 4), whilst mingled with them are numerous flakes of mica, black 

 bars and dark patches, and some quartz. The prisms, which appear 

 to be rhombic and show no dichroism, are possibly andalusite. The 

 light-yellowish parts near the upper edges of figs. 3 and 4 are quartz, 

 and contain some few liquid-cavities with vacuities. Fine brown 

 cracks frequently traverse the mass. 



3. Mica-schist. (Plate I. fig. 5, right-hand side.) — The passage from 



