128 Proceedings of the Royal Society of Victoria. 



Creek, near its junction with Sawpit Crully, are some huimiiocks- 

 of contorted gneiss. The rock [57; PI. XX., Fig. IJ examined 

 microscopically is shown to be highly contorted and traversed by 

 a series of small faults ; some bands in the rock are dark, owing 

 to the abundance of biotite, and they are separated by layers of 

 white quartz mosaic. 



Another type of the metamorphic rocks is represented at the 

 head of Twist Creek by some bands of contorted mica schists. 

 The rock [61] consists of alternations of quartz mosaic and of 

 greenish-white layers, which are intensely contorted, folded and 

 faulted ; the whitish layers are composed of packed crystals of 

 white mica with some indeterminable argillaceous material. The 

 rock originally contained many large simple grains of quartz ; 

 but the metamorphic action has altered most of them into 

 secondary mosaic. This change, in some cases, has only affected, 

 the margin of the quartz grains. 



The dykes in the metamorphic rocks are mostly coarse peg- 

 matites. A specimen [65] collected half way up the hill 

 above the stone quarry on the right bank of Commissioner's 

 Creek, is composed of large coarse grains of quartz, intergrown 

 with crystals of comparatively fresh orthociase. There are some 

 old felspar grains and abundant u)uscovite. The pegmatite 

 is traversing a fine schist of quartz and muscovite. A second 

 dyke [63] is of much coarser grain ; it consists of quartz, musco- 

 vite and orthociase, and contains abundant needles of tourmaline.. 



The rock of the ordovician series in closest contact with the 

 gneiss is a dark reddish-brown indurated slate [55] with len- 

 ticular bands of quartz. Most of the quartz occurs as a tine 

 mosaic, in which larger grains under polarized light show strain 

 effects. The bulk of the rock is a brown crumpled slate, iron 

 stained along lines which are roughly parallel. The constituents 

 of the base are small quartz grains in a cleaved argillaceous base, 

 containing minute crystals of authigenous mica. They appear 

 to have been developed owing to the re-arrangement of the 

 argillaceous material of the ordovician series. A less altered 

 member occurs at the junction between Sawpit Gully and Twist 

 Creek. It [62] is a crushed quartzose grit. Some of the 

 quartz grains have obviously been crushed in sifu, and there is 

 one thin band of quartz mosaic. There are numerous flakes of 



