587 



idomorpliie tourmaline and garnet and also of quartz and felspar. 

 No ground-mass is observed here, tlie larger felspars closely adjoining 

 each other and the small crystals of the other minerals and of felspar ' 

 are disseminated in those larger crystals. The garnets are idiomorphic 

 and microscopically colourless (in thicker sections they show a 

 light rose colour). Exceptionally they are partly surrounded by a 

 tourmaline-crystal, tourmaline-crystals enclosed by garnet also occurring 

 occasionally. As a rule, tourmaline in the granites shows a beautiful 

 zonar structure, with often rather distinct light-blue central pait 

 and a brown margin. Sometimes, between these zones an equally 

 distinct one of intermediate colour is found, or the colours graduate 

 into each other. Sometimes in zonar crystals a bluish central part 

 is seen with a pale-blue margin and an intermediate zone of light- 

 brown colour, differently coloured and repeatedly alternating zones 

 also being observed in some crystals. It is remarkable that in the 

 contiguous horiifels only brown and almost always homogeneously 

 coloured tourmalines occur. In the pieces of hornfels of the S'"' Lau 

 the zonar tourmalines were also found. 



The contact-rocks have been examined near the contact with the 

 granites. There they are dark to nearly black-coloured, and often 

 even macroscopically a high percentage of mica can be seen, whereas 

 between the granites and these rocks sometimes a rather narrow 

 transition zone is found which is rich in tourmaline. At the very 

 contact we often see a zone which for the greater part consists of 

 tourmaline. Farther away from the granites, biotite occurs more 

 frequently, the percentage of tourmaline decreasing at the same time. 

 The biotitehornfels at the contact of the larger intrusion contain, as 

 a rule, much tourmaline, whereas along the contact of a narrow 

 tourmaline-bearing vein in the upper-Lau no tourmaline but only 

 traces of biotite could be obberved as a contactphenomenon in 

 the schists, which for the rest were unaltered. The tourmaline of 

 the hornfels is almost always of homogeneous structure and of a 

 brown colour, exceptionally a marginal zone of daiker brown colour 

 also occurs, but zones of blue tourmaline like those found in the 

 adjoining granites do not occur here. Garnet is often found in con- 

 siderable quantity in the contact-rocks, especially near the granites. 



Sometimes between the quartztourmaline-rocks and the biotite- 

 hornfels a quartz-muscovite-zone was found of some mm.'s breadth 

 containing a small quantity of tourmaline, the muscovite of the zone 

 graduating farther from the contact into a mica of a pale brown 

 colour. 



