Geology of Mount Macedon. 191 



1. The Plutonic Rocks of the Palaeozoic Platforms. 



Aplin's map marks the occurrence of three outcrops of "granite" 

 in the Macedon area. The largest exposure lies along the south- 

 eastern border of the Macedon series. An outlier occurs to the 

 north of this main outcrop, and it also is on the boundary 

 between the eruptive rocks and the Ordovician. The third 

 exposure is low in the western slope, where a " granite " dyke is 

 marked two and a half miles east-south-east from Woodend. 



The south-eastern " granite " is well exposed on a ridge crossed 

 by the road from Riddell's Creek to Cherokee's. The rock con- 

 tinues from the State school reserve at Mount TenerifFe on the 

 south, to a low saddle half a mile south of Cherokee's. The rock 

 is also well exposed on the ridge between the head of Kerr's 

 Creek, (or Running Creek) and the Cherokee Road. 



The rock, as Aplin reuiarked, varies considerably in character. 

 A specimen from the ridge three-quarters of a mile south-west 

 from Kerr's Mill, at the head of Running Creek, shows the 

 following characters. The rock is of medium grain and holo- 

 crystalline. It consists of quartz, plagioclase and biotite. The 

 quartz is in large blebs and some idiomorphic crystals ; some of 

 them have solidified before the biotite. The plagioclase is 

 mostly oligoclase and belongs to two periods of consolidation ; 

 the crystals often consist of a worn, decomposed nucleus, restored 

 by re-growth with the outer zones in optical continuity with the 

 central part. The material of the nucleus has decomposed into 

 an irregular granular aggregate, with numerous minute microlites 

 of zoisite. 



Biotite is usually abundant ; it occurs in large well defined 

 crystals, and in microliths, some of which occur in zones round 

 the idiomorphic crystals of quartz and plagioclase. 



The specific quartz of this rock is 2 -8. 



As a second example of the rock fornung the south-eastern 

 plutonic outcrop may be taken a specimen from the south-western 

 margin at Hamilton's. The quartz is somewhat more abundant, 

 but is all allotriomorphic. The predominant felspar is oligoclase, 

 mostly occurring in irregular aggregates. There are also some 

 larger, simply twinned felspar grains referable to orthoclase. 

 The biotite at this locality is often decomposed into chlorites. 



