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capacity, dropping across a quartzite band in a highly metamor- 

 phosed condition would be very apt to ascribe it to a Plutonic 

 origin, as being the more simple explanation. Having no 

 intention whatever to gainsay the opinion of so able an 

 authority as Mr. Selwyn has proved himself to be in other 

 respects relative to South Australian geology, yet after a 

 careful investigation of any given band for a considerable 

 distance, the invariable conclusion has been favourable to its 

 sedimentary origin. Proof of their sedimentary origin can be 

 adduced as follows : — 1. Because of their uniform interstrati- 

 cation with the surrounding clay-slate. 2. Though fractured 

 extensively by lateral pressure, they still retain the outlines of 

 original beddings. 3. The quartz grains building up the lesser 

 metamorphosed specimens invariably bear a water - worn 

 appearance. 4. Though not abundant, characteristic water- 

 worn pebbles of a pre-existing quartzite have been found 

 imbedded within them ; also, on one occasion I found an 

 enclosed fragment of considerable size of a pre-existing clay- 

 slate. 



The foregoing, to my mind at least, fully establish the 

 sedimentary origin of the quartzites, and from the nature of 

 the deposits it is inferred that dry land existed not far away, 

 but in what direction it is scarcely possible to hazard an 

 opinion. This much might be inferred, from the small per- 

 centage of embedded pebbles within them, that in whatever 

 direction this ancient land was situate it did not present a 

 bold coastline. 



Clat-Slate. 



This class of rocks constitutes by far the largest moiety 

 of the fundamental rock system of the district. In some 

 cases the beds are found gradually passing from a fine 

 gritty quartzite to that of the characteristic slate. In others 

 the slates are divided from the quartzites or marbles simply bj 

 a flaky parting. Frequently metamorphism (which in no case 

 throughout the district of Munno Para has acted intensely) 

 has most powerfully affected the slates near their junction with 

 the quartzites, quartz reefs, nests, and strings of quartz. Near 

 their junction with the latter, frequently the slate has become 

 chloritised in character, slippery to the touch, and greenish in 

 colour. Where metamorphism has acted moderately, especially 

 where soda and other allied chemicals are present, the slate beds 

 are in a state of rapid decay. Thirty years' observation has led 

 me to believe that in situations where these allied influences 

 are in unison abrasion of the clay-slate is going on at the rate 

 of several inches per century. 



