2 F. L. StllhueU: 



tinuous along the whole length of the anticlinal axes at -the surface. 

 The course of a lava upward is irregular, and as it rises through 

 the different levels of a mine it wanders at times both east and west 

 of the actual " centre country," but is seldom far away. So regularly 

 do the lavas follow the centre country that they have been of gi-eat service 

 to the Geological Survey in the mapping of these anticlinal axes, and 

 Mr. H. S. Whitelaw (7) has tabulated the surface characteristics of the 

 lavas which are always decomposed and recognised by (1) the trench 

 or gutter caused by their weathering more easily than the walls of the 

 adjoining country rock, (2) their more stable decomposition product, 

 the magnesium carbonate, which at the surfa.ce occurs in thin nodules 

 or veins, and (3) the peculiar opaline aspect often induced in the quartz 

 of a reef with which they have come in contact. 



Observed in one anticline they are frequently found to branch into 

 two or more lava streams which may or may not junction again at 

 higher levels. At the New CTaristmas shaft, situated on the Christmas 

 anticlinal axis at Kangaroo Flat, six lavas are met in one small crosscut 

 of 94 feet, revealing the existence of quite a network of streams. 



In thickness they average from 9 inches to 12. Th.ree-inch seams are 

 not uncommon, and they range down to thin threads which may die 

 right out. Mr. Dunn (2) records a 5-foot lava in the Great Britain Mine. 

 The south shaft of the New Christmas Mine contains a lava 6 feet thick. 

 A 1 2-foot lava was supposed to exist in the Bird's Keef Mine, Kangaroo 

 Flat, but has been found to be in part sandstone, and is only 5 or 6 feet 

 thick. 



The trend of these dykes, north and south, is remarkably persistent, 

 and they form a parallel system of the " plateau region " type. The 

 parallelism is made particularly noticeable by its coincidence with the 

 direction of strike of the rocks. With this parallelism we do expect 

 to meet them in anticlines rather than synclines, for anticlines are 

 always in a state of relative tension to the synclines, and, therefore, 

 suffer fracturing in the relief of orustal stresses in prefei-ence to the 

 synclines. The coincidence of the strike of the rocks and the dykes 

 means that the same kind of crustal stresses have been involved in the 

 folding of the rocks, and in the injection of the igneous material. The 

 main earth movements resulting in the folding have resulted from 

 pressure fronu easterly and westerly directions. The rock stresses which 

 were relieved l)y the injection of the dyke material, and which no doul)t 

 result in rock fracturing, in part, have developed at a later date from 

 the same direction. I think this instance forms a good Victorian 

 example of Harker's principle of the intimate connection between 

 igneous action and crust movements (8), especially if we agree with T. C. 

 Chamberlain that earth movements are inheritances, and likely to lie 

 continued' in the same manner at different jieriods of the earth's history. 



