470 PROCEEDINGS OF SECTION C. 



rocks generally seem to require that the Cox's Bight series be placed 

 among the Algonldans. A possible exception is the muscovite schist 

 of the Black Point, which may prove to be a gneissified schist. 



There are some slates and sandstones in the same area, and the 

 fact of the processes of regional metamorphism having impressed on 

 the rocks, clearly of sedimentary origin, characters so different from, 

 those which we see in the mica schists might lead us to attribute an 

 eruptive origin to the latter. But repeated alternations of schist and 

 quartzite sometimes take place every few inches in such a way that, 

 if we consider the one to have been a sediment, we must say the same 

 of the other. 



The mica schist has probably been formed from an altered sedi- 

 ment such as clay, and the quartzite evidently represents sandstones. 

 Those sediments we may imagine were from the decomposition of 

 Archaean rocks, of which now no trace remains. This series of crystal- 

 line schists and quartzite continues westward to South- West Cape, 

 and eastwards certainly as far as Louisa Bay, if not as far as the New 

 River. But, taking the minimum width as 15 miles, and assuming 

 that no large anticlinals exist, the least thickness of the beds must 

 exceed 13,000ft., if the average dip is not less than 10 degrees. 



QUARTZITE AT ROCKY CAPE. 



A series of quartzites and quartz schists is exposed along the 

 north-west coast of Tasmania, from Jacob's Boat Harbor west of Wyn- 

 yard to Rocky Cape, which forms a promontory on the east side of the 

 bay extending to Circular Head. 



The Rocky Hills constitute a high range of quartzite which trends 

 south or a little east of south to about a mile south of the main road, 

 when it sinks rather abruptly and subsides in the geologically un- 

 known country which extends south across the Arthur River towards 

 the Heazlewood and Long Plain. Immediately west of the cape are 

 contorted quartz schists, which apparently belong to the complex of 

 schists and quartzites which are seen succeeding each other on this 

 part of the coast. 



The Rocky Cape quartzites resemble those of Cox's Bight, but that 

 in itself gives no very decisive help in correlating them, except that we 

 cannot match them in our known Silurian or Ordovician strata. Their 

 strike, however, is east of north and dip north of west. There is some 

 reason for doubting that they belong to our Palseozic series ; they have 

 been looked upon as of Pre-Cambrian age. 



The above have come under my notice since the last meeting of 

 the Association. There are other occurrences in the island which 

 most probably belong to the same system, but too little is known of 

 them as yet to hazard any statement on the subject. 



The conclusions in this paper are based mainly on lithological 

 and analogical considerations, and it must be admitted lack the strength 

 and certainty which can only be given by stratigraphical evidence, 

 for the present, unfortunately, not attainable. 



