GEOLOGY OF TASMANIA. ' 63 



further investigation. Its tendency to assume laminated 

 forms indicates that it was involved in the foliation of the 

 Silurian rocks. Its connection with our granites has not 

 been worked out. It is placed ^vith some hesitation at 

 the close of the Silurian. 



A belt of felsite, a little to the west of this zone, can be 

 traced through Mounts Read and Black, across the Pieman 

 River, at the raihvay crossing. The green augite-syenitic 

 rock at Lynchford has probably some connection with the 

 felsites. 



Devonian. 



3. Dial Range and West Coast upper conglomerates. 



2. Soft slates at Fingal. 



1. Granite in North, East, and West Tasmania. 



Our granites are considered to be of Lower Devonian age, 

 i.e., soon after the close of the Silurian. No granite intru- 

 sion into Permo-CarT)oniferous strata has been observed, 

 while it is frequently intrusive into the Lower Silurian 

 slates, and has been established as intrusive into Upper 

 Silurian at Middlesex. Evidence has been forthcoming 

 recently, at the Heazlewood and at Mount Agnew, showing 

 that the consolidation of the granite was subsequent to that 

 of the gabbroid rocks. There is an exposure of granite, 

 generally tin-bearing, running down the eastern side of the 

 island from Mount Cameron and Mount Stronach to the 

 Blue Tier and Ben Lomond, St. Marys. Seymour, Bicheno, 

 Freycinet's Peninsula, Maria Island, as far south as the 

 Hippolyte rocks. It occurs again in the Middlesex Field, 

 at Granite Tor, Mount Farrell, Hampshire Hills, Mount 

 Housetop, Magnet and Meredith Ranges, Mount Heems- 

 kirk, Mount Darwin, and evidently underlies the whole of 

 the West Coast. The quartz-porphyry dykes at Mount 

 Bischoff, the tourmaline lodes at Mount Black, Renison Bell, 

 and elsewhere in North Dundas, the sta unite lode and 

 spherulitic quartz reef at Zeehan denote the granitic reser- 

 voir below a large portion of the mineral fields on the West 

 Coast. The normal granite is a dark mica one, mostly 

 spotted with large porphyritic crystals of orthoclase felspar. 

 In its tin-bearing varieties the magnesian mica disappears, 

 and gives place to muscovit© and lithia micas. 



The Fingal slates, of a soft sandy nature, have been 

 doubtfully retained in the Devonian, on the strength of a 

 fossil resembling Anodonta jtikesii; but it is uncertain 

 whether they can be stratigraphically separated from the 

 Silurian slates at Fingal. 



