Bone Clay and Associated Basalts. 11 



Another possible explanation is that the abrupt conclusion 

 of the wash is due to subsequent movement and a lowering 

 of the volcanic materials bodily. The slight disturbance of the 

 clay and ash beds in the intermediate level, and the greater 

 disturbance and apparent drag at the boundary of the Ordo- 

 vician, would favour this, though the superincumbent weight 

 of basalt might account for much movement and compression 

 of the underlying soft material. The occurrence at the No. 8 

 workings of a lead dipping both ways also indicates changes of 

 relative levels. If that lead falls north naturally to the 

 Devonshire lead, it would indicate a subsidence to the south. 



The abrupt conclusion of the wash and the position of the 

 ejectamenta are then referable either to an actual vent, and 

 succession of vents, or to local subsidences in the neighbour- 

 hood of a volcanic vent. 



The depth of the bottom level does not preclude the possi- 

 bility of a valley with an outlet to the Yarrowee lead e.xisting 

 below it, even apart from any movement. The surface level 

 is here 1337ft. above sea level, and the bottom level 1017ft. 

 At the No. 3 shaft of the old company the surface level is 

 1227ft. and the main gutter 280ft. below, or 947ft. above sea 

 level. 



Surface Materials. — The surface directly over the mine, is a 

 basalt strip, which extends from Buninyong southward and 

 slightly westward, to the south-west corner of the Buninyong 

 Estate. It is bounded on the east, through the Buninyong 

 Estate, by the Devonshire Creek, which nowhere crosses it on 

 the surface. The surface of the basalt is somewhat uneven, 

 but has a general and considerable fall of almost 100ft. to the 

 mile southward. East of the creek the surface is for the most 

 part Ordovician, more or loss covered by recent alluvium, but 

 to the south-east of the No. 1 shaft is a hill marked by Mr. 

 Murray as a point of eruption and known as Webb's Hill. 

 From it two spurs run to the north-west and west, covered by 

 volcanic ejectamenta, in which blocks of the Ordovician bed 

 rock, usually micaceous, predominate on the north-west spur. 

 On the other is an outcrop of vesicular lava, perhaps a dyke. 

 There is no visible olivine present in any of the vesicular lavas 

 and scoria on this hill, whicli is in striking contrast to the 



