Rocks of Noyang. 67 



and the relations of the palaeozoic formations in it, cause me 

 to believe that these intrusive masses date from the great 

 age of plutonic disturbance that embraces the close of the 

 Silurian and the greater part of the Devonian period. Thus 

 the formation of these rocks would have taken place in an 

 age which, in Gippsland, was one of great volcanic activity. * 

 The occurrence of dykes and masses of quartz-porphyrites 

 radiating from the same place where subsequently other 

 masses of felsophyrite rocks (lavas) appeared, together with 

 breccias, suggest that this spot formed one of the vents of a 

 paleeozoic volcano, whose site is now indicated by the great 

 mountain mass of the Mount Elizabeth Range. It is not at 

 all improbable that the enormous masses of ejected volcanic 

 materials between Noyang and the Buchan River, some of 

 which are within a distance of fifteen miles of the place I 

 describe, may have in part been derived from this source. 



The igneous rock masses of Noyang, as a whole, cover a 

 far larger area than that which I have mapped and described, 

 and are encircled, and I doubt not were once wholly 

 enveloped, by the more or less altered Silurian sediments. 

 These have evidently been subject to violent strains and 

 compression, so that the bedding now lies in places at more 

 than 45° to the normal strike of the district. These dis- 

 turbed sediments have been invaded by the igneous rocks, 

 which have not only truncated their horizontal exten- 

 sions and have sent into them dykes and masses, but have 

 also melted off and absorbed an unknown amount of the 

 vertical extension downwards of the folded and compressed 

 strata. 



The igneous rocks which at Noyang thus intruded into the 

 sediments varied as to their structure, but they all belong, 

 with one exception, to the same petrological group, although 

 formed at different and successive parts of the same period 

 over which the invasion and metamorphism of the sediments 

 extended and the subsequent cooling and crystallisation took 

 place. The igneous rocks of Noyang must be considered as 

 a whole. The several varieties of rock have been, no doubt, 

 produced at different times, but these times have been merely 

 parts of a great series of periods of activity and quiescence, 

 and the difference in the composition and structure of the 

 rocks thus formed must necessarily have depended in great 



* " The Devonian Eocks of North Gippsland," Progress Report, Geological 

 Survey of Victoria, Part III. 



