THE VICTORIAN NATURALIST. 161 



tributary of the Hopkins River. Other small creeks enter at 

 various points. The lake level is about 1,245 ^ eet above sea 

 level. 



The railway station is situated about half-way along the north 

 side. The main road from Ballarat to Ararat also skirts the 

 north side. At the north-west part of the lake good sections of 

 volcanic tuff are exposed. The first evidences are at the old 

 Picnic Hotel, where some of the buildings are built of it. The 

 culvert over a small creek is also built mainly of the same 

 material. 



Description of the Sections. — No tuff was noticed to occur 

 east of a small creek at about 13%' miles from Ballarat, near 

 Stuart's Hotel. At the back of the hotel a cliff begins which 

 continues nearly half a mile, to Stuart's Point. We may speak of 

 this as Stuart's Cliff. This cliff is composed entirely of pyro- 

 clastic materials — tuffs, with fragments and blocks of all sizes both 

 of basalt and of the granitic rocks which form the foundation on 

 which they rest. The tuffs vary in the size of the rock fragments 

 they contain, but all the beds are firmly coherent, and the 

 fragments, embedded in a finer paste, are mostly compact, not 

 scoriaceous, basalt. Blocks of very vesicular rock, much de- 

 composed, also occur, containing much aragonite, both in radiating 

 crystals and masses and in globules. Calcite also occurs similarly. 

 Both calcite and aragonite also occur in the tuff itself. .White 

 veins of calcite with a combed structure occur between the tuff 

 beds at places, and veins of gypsum at one place. Nodules of 

 very impure limestone with dendritic markings are common, and 

 in some cases appear to have been formed in the tuff. 



The blocks of granite and similar rocks especially attract atten- 

 tion, though in reality not so abundant as the basalt blocks. 

 They vary from minute fragments, recognizable as granite or 

 granitic minerals, to blocks of several tons weight ; the largest 

 measures about 8x5x4 feet, and contains at a moderate 

 estimate 10 tons. The prevailing variety is a coarse porphyritic 

 granite. Large felspars are so abundant that the rock at times 

 appears to consist of felspar with interspaces filled with granite 

 rather than of felspars scattered in a granite matrix. A feature of 

 the porphyritic felspars is the excellent examples of the character- 

 istic simple twinning of orthoclase. Mica is frequently included 

 in these large felspars. The felspar varies in colour from flesh-red 

 to pale yellowish shades and white, and the general colour of the 

 granite varies accordingly. The finer matrix in which they are 

 embedded is rich in quartz. Occasionally distinct stout prismatic 

 crystals of biotite are found. 



Non-porphyritic granites also occur, often of finer texture, 

 passing by diminution of mica into aplite. Some of the aplites 

 are distinctly pegmatitic in structure. (A variety with very 



