466 PROCEEDINGS OF SECTto>J c. 



18.— THE DYKES IN TOWNSVILLE DISTRICT (NORTH 

 QUEENSLAND), AND THEIR RELATION TO SUR- 

 ROUNDING ROCKS. 



By JOHN FEWTBELL. 



19.— PROBABLE PRE-CAMBRIAN STRATA IN TASMANIA. 



By W. H. TWELVETREES, F.G.S., Government Geologist, Tasmania. 



Progress in our knowledge of tlie geological systems as developed 

 in Tasmania is made slowly, partly on account of the difficult nature 

 of the country, much of the island being uninhabited and covered with 

 dense forest broken by mountain ranges and scarred by deep ravines ; 

 partly, however, owing to State financial considerations, in consequence 

 of which State geological investigations are chiefly restricted to economic 

 and industrial matters. Now and again visitors, as well as resident 

 geologists, contribute some valuable papers to our literature, and some 

 distinct advance is made outside the range of official work ; but we 

 have to deplore the absence of continuous organised effort in pure 

 geology. Hence much of our knowledge is necessarily scrappy, the 

 large tracts which exist between mining centre are neglected, and 

 geological information accumulates in a desultory piecemeal fashion. 

 This must be accepted as an excuse for the somewhat disconnected 

 nature of the following remarks. 



PRE-CAMBRIAN. 



The stratigTaphical succession of the more ancient strata has not 

 been worked out, and great caution is advisable in giving definite ex- 

 pression to opinions. It is not certain that exposures exist of rocks 

 belonging to the Archaean complex, i.e., Pre-Algonkian. 



Rocks generally referred to the Pre-Cambrian are the following : — 



1. Gneissoid hornblendic schists at the Rocky River. 



2. Hornblendic schist, on the Forth River. 



3. Quartzite and mica schist, at Cox's Bight and in the Port 



Davey district generally. 



4. Quartzite,' at Rocky Cape, North- West Coast. 



1. Rochj River Schist. — These strata are met with on the Waratah- 

 Corinna Road, at 26 miles from Waratah, and continue to the 31| 

 miles, with a strike about N. 20° W. and a N.E. dip. 



The observed width of this zone is about a mile and a half. On 

 the east side they are bounded by the Pre-Silurian Long Plains series 

 of quartzite talcose and graphitic schists. The country to the west 

 has not been examined carefully, but slate and quartz schist 'are known 

 to occur. 



The Rocky River schists continue north-west for 10 miles to the 

 Rio Tinto Mines on the Savage River, and perhaps three or four miles 



