136 THE GEOLOGY OF TASMANIA— THE PRE-CAMBRIAN. 



quartzites, in such a way that the vrhole group must be 

 considered together as a series of sediments formed by 

 aqueous agencies. The interstratification of the schis- 

 tose conglomerates and the geneticahy related argil- 

 laceous, micaceous, and quartzitic schists is perhaps 

 most clearly displayed on the northern coast, near Ulver- 

 stone. There the beds are tilted, so that they stand on 

 edge, and the succession of the several varieties is seen 

 to be just such as is usually found where sediments have 

 been deposited tmder varying conditions. 



The variety displayed by these schists of finer grain 

 is remarkable. The nature and proportions of the con- 

 stituent minerals, and the degree of schistosity acquired, 

 all vary from point to point. 



Most commonly the schists are constituted of an 

 aggregate of quartz and a sericitic mica. These quartz- 

 mica schists pass on the one hand, by insensible grada- 

 tions, into pure quartzites, and on the other into mica 

 schists. The intermediate varieties are characteristic of 

 the series as a whole. 



The quartzite-schists are at times remarkable for the 

 perfection of the cleavage which they display, the de- 

 velopment of the mica being such that thin flakes, no 

 more than a millimetre in thickness, can be successively 

 detached. In some cases this fissile schist exhibits a 

 minute but elaborate puckering, which shows admirably 

 the nature of the stresses to .which the rock has been 

 subjected. This latter variety is especially noticeable 

 on the Linda Track, between the Collingvvood and 

 Franklin Rivers. 



The argillaceous schists are widelv distributed 

 through the regions occupied by these Pre-Cambrian 

 rocks, and are especially abundant in the neighbour- 

 hood of Cox's Bight. They show clearly, in some cases, 

 the original planes of stratification, and are little dif- 

 ferent in any particulars from unaltered shales. In other 

 cases these argillaceous varieties have had a slaty 

 cleavage impressed upon them, and are converted into 

 true slates. 



They merge into schists, in which mica predomi- 

 nates. These possess a colour which usually varies be- 

 tween pale green and yellowish grey, and possess a 

 greasy feel. The quartz is commonly restricted to len- 

 ticles and wavv bands. Other varieties are reddish from 



