240 



them to be probably Palaeozoic. The Tertiary basalts of Kan- 

 garoo Island and the Mount Gambier area have no analogy 

 to the Blinman melaphyres, but the basic dykes of the Mount 

 Lofty Ranges, many of which have become amphibolites and 

 are almost certainly Palaeozoic, have most distinct similarity 

 to the rocks under consideration. For example, a specimen 

 of the wide dyke in the gorge by the New Era Mine, near, 

 Woodside (for which I am again indebted to Mr. liowchin), is 

 porphyritic in character. Its base is composed of secondary 

 amphibole, basic plagioclase felspar, quartz biotite, magne- 

 tite, and sphene ; while the phenocrysts of felspar are almost 

 entirely altered to an aggregate of epidote and scapolite. 

 The uralite diabase of Port Elliot *i8) and the dyke by Din- 

 ham's farm, Ardrossan, may also be of this series, as well as 

 the dykes near Mount Barker and Reefton Heights (com- 

 posed of basic plagioclase, secondary hornblende, and a little 

 sphene), or that described by Dr. Chewings from Mount 

 Pleasant. (19) 



These considerations lead me to conclude that the Blin- 

 man basic igneous rocks are Palaeozoic in age. Their present 

 position, as described by Mr. Howchin, and their mineralog- 

 ical metamorphism might be due to the metamorphism they 

 had undergone under an over-burden of probably Mesozoic 

 sedimentation, now, with the exception of the Leigh Creek 

 area, completely stripped off. That they all originated 

 near the present land surface is disproved by the gabbroid 

 texture of some of the dyke rocks, which texture could have 

 been induced only under almost plutonic conditions. Should 

 any of the basic dykes by Leigh Creek be traceable up to the 

 boundary of the Mesozoic sediments, their truncation or con- 

 tinuance into these will completely prove or disprove my 

 theory, if the identity of the Leigh Creek and Blinman 

 eruption periods be allowed. I much regret that my removal 

 from South Australia prevents my obtaining this crucial evi- 

 dence. 



In conclusion, I beg to thank Mr. Howchin for the op- 

 portunity of examining these interesting rocks. 



Postscript. 



Mr. Howchin has forwarded to me a specimen of an 

 amphibolite intrusive into the Pre-Cambrian area at Mount 

 Compass, fifteen miles north-east of Yankalilla. In hand 



(18) Dr. C. Chewings, Ein Beitrag; zur Kenntniss Greologie 

 Slid- und Central-Australiens. Heidelberg, 1894. 



(19) Op. cit. supra. 



