xlvi. 



by fossiliferous limestones of the Lower Silurian epoch. And 

 though the lower series underlying the fossiliferous limestones 

 and associated strata about Ardrossan cannot be brought into 

 direct relationship with the fundamental rocks on this side of 

 St. Vincent's Gulf, yet their mineral character and sequence 

 place them in accord. And the same may be said of the rocks 

 constituting the high lands on Eyre's Peninsula. 



Evidences of a missing chapter in the geological history of 

 this province are afforded by the occurrence of rolled pebbles of 

 stratified rocks in the oldest known of our sedimentary deposits. 

 These are well-rounded quartzite pebbles, discovered by Mr. 

 Scoular in the grit bands in the basal beds of the Gawler hills, 

 and subangular pebbles of gneiss in the siliceous clay-slates at 

 Hallett's Cove. 



Associated Eruptive Hocks. — Though I have expressed the 

 opinion that the great masses of granites, eurites, and syenites 

 associated with the metamorphic strata of the Adelaide chain 

 are probably altered sedimentary rocks, yet I do not wish it 

 to be understood that all South Australian granites are to be 

 included in that category. One undoubted dyke of granite is 

 that which forms the headland of Rosetta Head, and Granite 

 Island, and is continued to Port Elliot ; its intrusive origin is 

 obvious by the veins passing from it into the adjacent mica 

 slate, fragments of which are also found entangled in it, and 

 particularly by the circumstance that its course cuts directly 

 across the line of strike of the mica slate and clay-slates. 

 According to Mr. Burr, a similar granite is visible above water 

 at Cape Jaffa and at Cape Morard de Galles. 



Granite dykes of small dimensions, but numerous, traverse 

 the sandstones and metamorphic rocks as you approach the 

 extensive granite area at Palmer from the west ; but the two 

 rocks are mineralogically very different. 



Intrusive rocks are, however, infrequent in the Adelaide 

 chain ; Mr. Selwyn noticed felspathic granite at Mount Bryant. 

 In the Elinders Range he observed a small greenstone dyke on 

 the east flank of Mount Remarkable, and Mr. Ulrich has 

 described dioritic dykes at three other places in the Elinders 

 Range to the north of Port Augusta. 



Lower Silurian Rocks. 

 Mr. Selwyn describes the whole of the country from Mount 

 Remarkable and Port Augusta, north-east of Mount Serle, as 

 occupied by sandstones, purple and grey shales, and siliceo- 

 calcareous beds resting unconformably on the more slaty series 

 which covers the surface to the southward. This unconformity 

 is illustrated by a sketch section of Mount Remarkable, the 

 description of which runs as follows : — " At Mount Remarkable 



