120 



If solely guided by geographical demarcation, tins band com- 

 pletes the Munno Para series to tbe east. As it happens in 

 this case the geographer's line of demarcation coincides badly 

 with the geologist's. Consequently, I have extended the cross 

 section rather over one mile into Para Wirra, embracing a 

 limestone band, an extensively developed series of quartzite 

 bands, and thus constituting a geological line of demarcation 

 between the less metamorphosed clay slates of Munno Para, 

 and the mica-schists of Para Wirra. 



Origin. — A singular coincidence, one that has not escaped 

 the keen eye of Professor Tate — see his Presidential address 

 for 1879 — is that the fundamental rocks when followed 

 easterly in the direction of their prevailing dip become more 

 highly metamorphosed ; for it is true that vast accumulations 

 of granite and granitoid rocks, whether of Plutonic or Meta- 

 morphic origin, are distributed throughout the old sedimentary 

 rocks constituting the range on the west of the River Murray. 

 That the superabundant heat arising from what we see of these 

 outbursts conveyed direct should have effected the condition of 

 the strata so far west as the western boundary of Para "Wirra 

 is very improbable. Nevertheless, I am of opinion that the 

 same fiery energy which produced the granite and granitoid 

 rocks of the Murray Range, effected at the same time the 

 metamorphism of the Para Wirra beds from a deeper seated 

 point. A bed of rock on the surface in Para Wirra, from its 

 natural inclination, as it extends east becomes deeper buried 

 beneath succeeding beds, and also nearer the seat of Plutonic 

 energy. Therefore, the bed which at the surface in Para Wirra 

 represents a mica-slate, in all probability at a moderate depth 

 represents gniess, at a greater granitoid, and at still greater 

 depths, and also proceeding into closer proximity to the super- 

 heated mass, a true granite. In this manner, though youngest 

 in the series, the Para Wirra rocks may have been affected by 

 capillary conduction of heat directed through the plane of 

 original bedding, though placed at considerable distance from 

 the scene of actual fiery activity. Another theory might be 

 propounded, which is also the most probable, that the fiery 

 energy that produced the granite and granitoid rocks to the 

 east occupied a deeper-seated horizon in the west as it 

 extended beneath the Para Wii'ra beds, and thus affected them 

 vertically upwards. 



Mr. A. R. C. Selwyn, in his valuable " Geological Notes of 

 South Australia," suggests that some at least, if not all, of our 

 quartzite bands might be looked upon as being metamorphosed 

 Plutonic rocks — a theory which cannot be applied to any of 

 the Munno Parra bands, unless possibly to one of them. A 

 flying excursionist, as Mr. Selwyn was whilst here in official 



