60 gec»lo(;y of Tasmania. 



Silurian. 



The divisions of this system are still largely tentative. 

 The following scheme, in which the eruptive rocks of the 

 period are included, must be taken as provisional : — 



Upper and Middle SUtirian. 



5. Quartz porphyries and f el sites at Mounts Darwin, 



Jukes, Ovx'en, Tyndal, Read, Red Hills, Black, 



Murchison, Farrell ; 

 4. Gabbros, peridotites, pyroxenites, and serpentine at 



Dundas, Trial Harbour; Heazlewood, Forth, 



Anderson's Creek ; 

 3. Brachiopod sandstone, at Middlesex, Heazlewood, 



Queen River ; slates, sandstones, and limestones, 



with meiaphyre lava, at Zeehan ; 

 2. Schists, conglomerates, and limestones, at Mount 



Lyell ; grey wacke series at Dundas ; slates and 



argillaceous schists, at Mounts Read and Black. 



Lower Silurian. 



1. Limestone, at Gordon River, Rail ton, Chudleigh, 

 &c. ; slates and sandstones, at Beaconsfield, Lefroy, 

 Mangana, Mathinna, Scamander, &c. 

 The Silurian system is strongly developed in Tasmania, 

 especially in the N.E., N.W., and Vv^. Owing to paucity 

 of fossils, its subdivisions are unreliable, except in a few 

 instances, and its boundary-lines with the Cambrian rocks 

 are still obscure. The lower division is represented on the 

 West Coast by the Gordon River series, and on the East 

 by the slates, in which our gold reefs occur at Lefroy, 

 Beaconsfield, Mathinna, &c. The limestones along the 

 Gordon River are fossiliferous, containing Favosites, Ortho- 

 ceratites, Ra'phistoma, Orthis, Rhynchonella, Euomphalus, 

 Mvrchi^onia,'kc. They reappear to the N.E. of Mount 

 Farrell in the bed of the Mackintosh, a short distance above 

 its junction with the Sophia River. The limestones of 

 Chudleigh, Mole Creek, and Ilfracombe are plaxed provision- 

 ally in the lower division. They are non-fossiliferous, and 

 the only way of fixing their age is to connect them strati- 

 graphically with the Caroline Creek Cambrian beds. The 

 slates and schists between the Heazlewood and Corinna be- 

 long to an undetermined horizon in the system, and some 

 of them may be pre-Silurian. The slate and schist reefs 

 which run out to sea on the N.W, Coast can only 

 vaguely be referred to as Silurian ; at Rocky Cape, they are 

 probably lower in the geological record. 



