284 Geology of 



Sometimes the melaphyres, principally where they occur in higher 

 positions, lie directly upon the edges of the palaeozoic rocks, but in 

 most instances, they are preceded by beds of tufa, which often are so 

 intermixed and blend so thoroughly with the decomposed sedimentary 

 rocks below them, that it is impossible to fix the exact line of contact 

 between them. These lowest beds are mostly wacke, more or less 

 amygdaloidal, of brown and reddish tints, in some localities they are 

 traversed by dykes of melaphyre of a compact texture. They are 

 overlaid by regular coulees or streams of melaphyre. We may consider 

 that some of the wacke and some of the amygdaloids are either ashes 

 deposited during submarine eruptions on the sea bottom, or if, at 

 least, some of them were formed by regular coulees they have after- 

 wards been so much exposed to hydrothermal action, that they have 

 undergone great alterations and changes in their structure, whilst the 

 melaphyres proper have been ejected during larger submarine erup- 

 tions, following each other in quicker succession than the former, by 

 which the whole series became more protected. Some of the streams 

 are of great thickness and extent, as I was enabled to trace them for 

 from five to six miles continuously. Their number is also very great, 

 into which fact the G-awler Downs, amongst other localities, give us a 

 splendid insight. There, streams of melaphyres, many of them standing 

 nearly vertical— a dip of 79 Q to 82°, generally to the E.S.E., being 

 common — alternate for several miles in an almost endless succession 

 with tufas of various character. Some of them, full of concretions of 

 green earth, are true amygdaloids, or are full of geodes of agate, 

 chalcedony, and all the numerous varieties of quartz usually found in 

 these old basic rocks, vividly reminding me of Oberstein, in G-ermany. 



The lithological character of the rocks under review is very varied. 

 "We find some of which the component parts are so distinctly 

 crystallized that they could be mistaken for dolerites, others are more 

 porphyritic, others so compact that they appear like basalts, whilst a 

 few of them have a pitehstone-like appearance. "When in an unde- 

 composed state, they are generally black, with greenish, bluish, or 

 reddish hues. They contain numerous minerals as accessories, such as 

 agate, chalcedony, amethyst, jasper, calcareous spar, sphaerosiderite, 

 delessite, and epidote, but I was unable to find any traces of ores, and 

 the different localities which were pointed out to me as containing 

 copper ores proved unfortunately to consist only of masses of green 

 earth, as accessories to the rocks, or colouring them intensely. 

 Concerning their position, they are invariably found to be below the 



