and their Contact Zones. 57 



mass. This mica is colourless, and reacts like nmscovite. 

 No hornfel that I have examined is without more or less 

 magnesia mica as brown dichroic plates, which, however, 

 are usually confined to the ground mass. I have not any- 

 where observed the interlacing thorn-like microliths which 

 are so plentiful in the true nodular schists near at hand, 

 excepting in one instance at the lower part of Sheep Station 

 Creek, where I observed a few. Other microliths are pro- 

 bably minute mica plates, apatite needles, and colourless, 

 imperfect crystals, whose nature I am unable to determine. 

 In one example of hornfels taken from the immediate con- 

 tact at that place where the amphibole granites have trun- 

 cated the strata, I also observed very many minute black, 

 dark green, or dark brown microliths, having brush-like 

 terminations at one or both ends. These occurred generally 

 in such manner that two or three crossed each other, thus 

 forming a radiating group. On a very small scale, but 

 much darker in colour, they bear much resemblance to 

 bladed and also radiating amphibole (actinolite ?), which I 

 have observed in a compact diorite near Bright. Perhaps 

 these may be referred to the same class.* In another 

 sample of schistose hornfels taken from near the same place, 

 I observed spaces which were perfectly clear and colourless 

 by ordinary light, but which, by polarised light, seemed at 

 first sight to be mainly isotropic. On, however, using a 

 higher magnifying power I found these spaces to break up 

 into slightly discordant plates, which were certainly, 

 although slightly, doubly refracting. The quartzose horn- 

 fel is composed, more or less, of irregular granules of quartz 

 of the character of those of the normal sandstones. I 

 observed no fragments of the felspars intermixed with them. 

 The quartz granules composing this kind of hornfels are set 

 in what was once a more or less plentiful paste, which, in 

 the least-altered examples, resembles that which I have 

 observed similarly placed in the Silurian quartzose sand- 

 stones of the district. The changes which have taken 

 place in this paste are analogous to those I have 



* See as to these microliths Zirket Mikrosliopische Beschaffenlieit der 

 31ineralien, 1870, p. 491. In an example of nodular schist from Swift's 

 Creek I have also found numbers of these acicular microliths; examined 

 with a power of 350 linear, I found the larger ones to be yellowish brown 

 in colour, and distinctly dichroic. The minute size, '0015 x "0003 inch, 

 rendered it impossible to observe whether the plane of vibration coincided 

 or not with the direction of the sides. The smaller individuals still 

 appeared merely as black lines. 



F 



