Dykes of Marble and Quartz. 203 



stated to be 47 yards; its dip, 50° SW.; and its strike, 

 S. 22° E. Alternations of quartz rock and crystalline white 

 and grey marble compose this dyke ; innumerable lines and 

 scratches mark the edges and face of the marble ; and the 

 quartz has also been subject to a semicrystalline action, the 

 surface being crumpled or doubled up into parallel anticlinal 

 ridges." There appears to be no line of demarcation trace- 

 able between the quartz and marble ; and the two together, 

 after descending into the bed of the river, suddenly curve 

 round and re-enter the granite as a second dyke. Traces of 

 green carbonate of copper are found associated with the other 

 minerals of this dyke. 



The author considers that the scratches and furrows 

 which he has observed, and other phenomena in the line of 

 dip, could not have been in existence before the formation of 

 the present river channel. 



A second dyke is then described, in a place where the rocks 

 are thrown into great disorder, and the author details some 

 changes which have produced singular conditions of mineral 

 structure. He also supposes that they exhibit marks of a 

 gradation existing between limestone and quartz. A third 

 dyke of the same character is then mentioned, in which the 

 constituents of the granite are mixed up with the calcareous 

 rock ; and the author states, that, near these dykes, the gra- 

 nite assumes a distinct character, a greater proportion of fel- 

 spar, and less mica, being present. 



At Jaoramin, higher up the river than the spot just al- 

 luded to, the structure of the rocks is described as somewhat 

 different, the felspar being less completely mingled with the 

 other minerals, but the rock occasionally passing into por- 

 phyry. Where it is not denuded, the rock, however, is here 

 overlaid by a mass of conglomerate, from 200 to 300 feet 

 thick, through which the river makes its way. At St Peters 

 are low hills, more decidedly granitic. T*Jear Stuckeys farm 

 are numerous fragments of crystalline rock, the surface of 

 which is much worn, as is the case with other calcareous 

 rocks all over New South Wales. No traces of fossils have 

 been found in these limestones. 



The author remarks, that the greenstone becomes compact 



