BY L. KEITH WARiD, B.A., B.E. x^3 



Dundas slates on the western slopes of the mount (i). 

 TJnfortunateh^ the junction of the siliceous sediments 

 which form the backbone of Mount Farrell with the 

 quartzite schists on the other side of the valley of the 

 Sophia River, is hidden by the later sediments. But 

 the sequence displayed by this section is significant. 



The relationship between the Cambrian sediments 

 of the Beaconsfield district and the schists of the Asbes- 

 tos Range is shown diagrammatically in a section (2). 

 The relationship is, in part at least, masked by an in- 

 trusion of serpentine and aplite between the rocks of 

 the two systems. 



The porphyritic igneous rocks, which have now been 

 observed at Mount Farrell (3), Gunn's Plains (4), and 

 North Dundas (5), to be contemporaneous with certain 

 members of the Dundas slate series are only known as 

 intrusives in the quartz-mica schists. 



The rounded pebbles of the West Coast Range con- 

 g"lomerate are composed of fragments of the quartzites 

 and quartz-mica schists described below. All of the 

 more durable varieties of these latter rocks are repre- 

 •sented in the conglomerate. 



We may, therefore, in summing up the evidence 

 collected, state the following facts : — 



(a) Whatever may be the inter-relationship of the 



several groups here referred to the Cambrian 

 system, there is one feature which they pos- 

 sess in common — viz., where an actual contact 

 has been observed, they are found to occupy a 

 higher stratigraphical position than the schists, 

 now for the first time strictly termed .Pre- 

 Cambrian. 



(b) The Cambrian formations are separated from 



the subjacent schists by a strong unconformity 

 wherever contacts have been observed. 



(i) See Section IV. Also Geological Survey of Tasmania, 

 Bulletin No. 3. 



(2) See Section III. 



(3) Geological Survey of Tasmania, Bulletin No. 3, pp. 17 

 ■and 34. 



(4) Geological Survey of Tasmania, Bulletin No. 5, p. 9. 



(5) Geological Survey of Tasmania, Bulletin No. 6, pp. 17 

 •and 38. 



