156 A Physical Description 



characterised by Thinnfeldia (Jerusalem) ; the other, Per- 

 mian (?), with Glossopteris, &c. 



Carbonaceous Sandstone. — In the Oatlands district there 

 is a tableland forming an inclined plane, of which the 

 highest portion is Lake Tiberias. This is about 1460 feet 

 above the sea. The floor of this plain is almost entirely 

 composed of sandstone, which very closely resembles the 

 Hawkesbury rocks. The strata are in two divisions slightly 

 uncomformable to each other. The upper beds are formed 

 of a fine grained sandstone, more or less ferruginous, in thin 

 layers with much false beddings decomposing into a worth- 

 less soil from the upper beds. Small seams of coal and 

 carbonaceous bands are met with in the formation, just as 

 they are in a similar deposit in New South Wales. I have 

 no doubt on my own mind, from all I have seen of this 

 district, that the formations are the same. The town of 

 Oatlands is built upon it, and it is well seen round the 

 borders of Lake Dulverton. I am not aware how far this 

 formation extends in Tasmania. I never noticed it except 

 on the Oatlands tableland. It is not fossiliferous. I should 

 say it was of considerable thickness, 200 or 300 feet at least. 

 The line of junction between it and the coal formation is 

 well marked. They are not quite conformable ; the coal 

 measures having a slight dip to the south, which brings 

 them to the surface at the north side of York Plains. The 

 junction often shows pebbles of coal and rodled masses of 

 shale and coal measures, marking the denudation previous 

 to the deposition of the sandstone. Both formations are 

 very extensively overlaid by outflows of greenstone ; and no 

 doubt were an accurate geological survey to be made many 

 faults would be found as well. 



Greenstone. — The rock which bears this name in Tas- 

 mania no doubt belongs to several distinct groups of intru- 

 sive or metamorphic rocks. It plays such an important part 

 in the geological structure of the island that a detailed 

 examination will be necessary. Its appearance is certainly 

 posterior to the deposition of the carbonaceous sandstone, as 

 it breaks through that rock and overflows it. It forms the 

 capping of nearly all the mountains of the island, from which 

 we gather an important insight into the denudation to 

 which the rocks have been subjected. It is probable that 

 all these deposits of greenstone formed large, unbroken 

 deposits, covering much of the undulating surface of what is 

 now Tasmania. This may have been then a sea-bottom, 



