132 Geology of Hobart Town. 



The age of the several parts of the Tasmanian mountain 

 system is supposed to vary considerably, and evidence would 

 go to show that Tasmania, of a past geological epoch, had a 

 very different form from that which characterises it at the 

 present time. 



At first, it most probably appeared as a group of islands : 

 about five in number. In the succeeding epoch, much of 

 the intervening portion of sea bottom was elevated, and the 

 area existed as one continuous mass of land ; indented, 

 however, by at least' two deep bays. The first of these 

 extended from Campbell's Town to the sea ; the second, and 

 larger, occupied the valley of the Derwent, and much of the 

 surrounding district. 



These bays were, in time, filled by what appears to be 

 the carboniferous rocks of Tasmania, thus becoming the 

 future coal basins of the island. It is to the geological 

 features of the last-named basin that the following notes 

 bear reference. 



What may be termed the method of survey adopted, was 

 to traverse the country by a series of lines radiating from 

 Hobart Town as a centre. 



The first of these lines was along the main road, in the 

 direction of New Norfolk, a town situate on the Derwent, 

 about twenty miles from the metropolis. 



Leaving the coal seams of New Town on the left, there 

 were met with a succession of carboniferous sandstones and 

 shales ; cut by numerous dykes and masses of eruptive 

 green stone and black basalt ; or covered over by gravel 

 and other aqueous deposits until near Bridge water (ten miles 

 from Hobart Town), where is exposed a dense clay stone, 

 afterwards in turn succeeded by thick beds of highly fossili- 

 ferous limestone. The latter, after extending several miles, 

 and presenting a gradually rising series, apparently dip in 

 quite a contrary direction ; so that, after passing by masses 

 of river deposits and dykes of basalt, at New Norfolk, the 

 clay stone of Bridge water is again met with, and then, 

 towards Hamilton, are beds of sandstone, shale, and coal, 

 appearing in the reverse order of the succession passed 

 over in journeying from Hobart Town to Bridge water. It 

 would seem, therefore, that an anticlinal exists near the 

 latter place. 



A second line of route passed over Grass Tree Hill, towards 

 Richmond, displaying a somewhat similar series, only that 

 the limestone nowhere appears at the surface. 



