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



127 



III.— THE STRATI GRAPHICAL SUCCESSION IN 

 TASMANIA. 



It is necessary to consider briefly the succession of 

 the lower Palaeozoic strata and the relations of these to 

 the rocks here described, so that the grounds for the 

 classification of the latter as Pre-Cambrian may be pro- 

 perly appreciated. 



The recognised base of "the Ordovician system is the 

 " Gordon River Limestone." With this limestone are 

 associated sandstones and slates (i) which may belong 

 to the same system. 



This fossiliferous limestone at Railton and at the 

 Humboldt Divide lies directly upon the fossiliferous 

 Upper Cambrian beds. It is a persistent geological 

 horizon, and therefore of great stratigraphical im- 

 portance. 



The strata, to which an age greater than that of the 

 Gordon River limestone may be ascribed, whether on 

 palaeontological or on stratigraphical gro.unds, are 

 these : — 



1. The Dundas slate series — with the associated in- 

 trusive and effusive porphyritic igneous rocks. 

 These rocks may be equivalent with slates and 

 sandstones at the Needles, and near Mounts 

 Mueller and Wedge. 



2. The Caioline Creek beds, and their fossiliferous 

 equivalents discovered by Mr. T. Stephens on 

 the Humboldt Divide in the Florentine Valley. 



3. The " tubicolar " sandstone (commonly known 

 as the " pipestem " sandstone) ; and the " dis- 

 coidal " sandstone overlying it. 



4. The Denison Range conglomerates and quartz- 

 ites, tog-ether with the similar rocks constituting 

 the West Coast Range conglomerate series. The 

 pebbly sandstone and conglomerate of Railton 

 also probably belong to the same horizon. 



5. The sandstones, quartzites, slates, grits, and 

 conglomerates of Cabbage Tree Hill, Beacons- 

 field. 



(i) See Section III. 



