Physiography of Bulla Area. 333^ 



(b) In C: the pebbles lie regularly on their flat faces. 

 • (c) Pebbly, sandy and clay bands alternate. 



(d) Most of the stones are small. Not one large stone is seen. 



If it were glacial you would expect to find some boulders.. 



(e) Facetted and striated pebbles are extremely rare, 

 (fj Many strata contain pebbles of only one size. 



(g) The conglomerate is almost certainly of Silurian age, and 

 no other evidence of Silurian glaciation has been reported. 

 in Australia. 

 For the reasons above it seems more likely that the conglomerate 

 Ci is the basal conglomerate of, the Silurian rather than an Ordo- 

 vician glacial deposit. 



The material of which the pebbles are composed is similar to that 

 of the Kerri conglomerate found along Conglomerate Creek, near 

 Macedon (10). There are quartz, quartzite, black chert, quartz 

 porphyry, greisen and diabase pebbles. The Kerri conglomerate 

 contains a large percentage of dimpled and squeezed pebbles, whose- 

 state it has been shown is probably due to solution under pressure 

 (10). Many similar pebbles are found in C^ but most of the 

 dimples have not been made in situ, for frequently the dimples 

 are opposed not to a pebble, but to the clay matrix. A few of 

 the dimples may have been made in situ. 



Met amorphic Rochs. 

 These are exposed along Deep Creek to the north, west, and 

 south of the granodiorite. At and near the junction the sediments 

 have been converted into hornfels, Avhile further away they occur 

 as spotted shales, or as indurated sandstones or shales. The- 

 width of the aureole varies considerably, probably owing to the 

 irregular junction of the granodiorite, with the sediments beneath 

 the surface. As far as can be judged from the bedrock exposed 

 along the creeks the hornfels belt on the average appears to be- 

 about a quarter of a mile wide, and it gradually merges into 

 spotted slate, which is not uniform in its distribution. The ind\i- 

 rated sediments have abundant secondary mica. 



In the hand hornfels is a hard, dense, dark rock,- in which indi- 

 vidual crystals cannot be seen with the naked eye. ^ Under the- 

 , miscroscope, however, it is seen to have abundant secondary brown 

 biotite. Near the contact there is a considerable amount of cordie- 

 rite produced, but further away andalusite, biotite, and secondary 

 quartz predominate. The cordierite can be distinguished fromi 



