BY L. KEITH WARD, B.A., B.E. 



139 



With regard to the development of the&e rocks on 

 the South Coast of Tasmania, Mr. W. H. Twelvetrees 

 has estimated the thickness at 13,000 feet as a minimum 

 (i). This calculation is based on the assumption thai 

 no large anticlinal folds exist, and that the average dip 

 is not less than 10 degrees. 



During the recent western exploration work in the 

 neighbourhood of the Frenchman's Cap, the writer was 

 enabled to make some observations which should here 

 be recorded. 



The outstanding feature of the Pre-Cam'brian in that 

 region is the existence of a considerable thickness of 

 bedded quartzite schist lying in an approximately hori- 

 zontal position upon the top of the quartz schist, quartz- 

 mica schists, and micaceous or argillaceous schists. 



Viewing this thick layer of quartzite schist from the 

 tops of the ranges, one gains the conviction that it is a 

 single horizon, resulting from the alteration of a once 

 continuous horizon of sandstone. This horizon appa- 

 rently extended from the Raglan Range southwards to 

 the Frenchman's Cap and the Surveyor's Range, and 

 eastwards to a mountain (called by the writer A'lgonkian 

 Mountain) at the northern extremity of the Prince of 

 Wales Range, and slightly to the westward of the axis 

 of that range. Whether the white serrate peaks of the 

 Prince of Wales Range are on this horizon the writer 

 cannot say. 



Only the highest portions of the ranges mentioned 

 are composed of this quartzite schist, which in most 

 cases stands up boldly with precipitous walls above the 

 slopes carved in the softer schists. 



From a short distance the quartzite schist appears 

 to be a bedded sandstone, since the progress of weather- 

 ing accentuates the original bedding planes. But on 

 closer examination a slight schistosity is noticeable 

 throughout the rock. 



This horizon, as a whole, is not free from foliation, 

 »iid the best view of the folding is obtained from the 



(i) Proceedings A.A.A.S.. Adelaide. 1907, " Probable Pre- 

 Cambrian Strata in Tasmania," p. 470. 



