73 



well acquainted with this material, it is of wind-blown 

 origin, and of recent age. 



(h) Miocene (?). — The more conspicuous peneplains de- 

 scribed are probably of Micocene age, as the aggraded areas 

 are formed of fresh-water sediments, similar to those better 

 known in the vicinity of Adelaide. Pebble beds are fre- 

 quently interbedded with the clays, indicating proximity of 

 origin. On account of their soft nature these beds are much 

 cut into by the erosive action of the sea. 



(c) The Pre-Camhrian Complex. — With the exception of 

 the minor developments already described, all the rock ex- 

 posures known to us are probably of Pre-Cambrian age. The 

 data leading to this conclusion rests on petrological and litho- 

 logical grounds, as palgeontological evidence, except for nega- 

 tive information, is entirely wanting. The resemblance 

 which the Port Lincoln series of rocks bears to that classed 

 as Pre-Cambrian in Southern Yorke Peninsula is the main 

 support for this decision. In addition, the absence of any 

 beds of the recognized Cambrian series of the Mount Lofty 

 Ranges, and the extreme metamorphism displayed, aids in 

 this same conclusion. 



At Port Lincoln the strata trend uniformly in an almost 

 north and south direction, with a tendency to east of north. 



At Tumby Bay the rocks are chiefly meta-sedimentary, 

 and preserve a uniform N. 55° E. direction. There is a 

 distinct possibility, therefore, that these are two separate 

 series, the Port Lincoln rock being referable to an older 

 period. A careful survey of the intervening country will 

 alone settle this point. 



At Port Lincoln a great series of schistose rocks, chiefly 

 gneisses, is well exposed at Point Kirton, where quarrying 

 operations are in progress for the railway jetty under con- 

 struction. Here pure white, coarse-grained quartz-felspar 

 gneiss passes into a typical augen variety, with biotite de- 

 veloped? along the lines of crush. In places it is intricately 

 folded. Dark-g^rey basic bands, of fine-grained amphibole 

 granulite, sometimes many feet in thickness, run parallel with 

 the gneiss, sometimes isolated in the midst of the latter. 

 Occasional coarse acid pegmatite veins can be traced passing 

 obliquely across the foliation. One of the most notable fea- 

 tures in the vicinity is the occurrence of a biotite-bearing 

 pilotaxitic dolerite dyke, about 30 feet wide, running with 

 the series. For the most part this rock is entirely fresh, 

 thou8:h along certain cracks uralitization was noted to have 

 commenced. No clue to its agje is forthcoming. It cannot 

 be very ancient, certainly not comparable in this respect with 

 the intruded rocks. 



