Ii6 A Physical Description 



there is no vestige of any marine formation of later 

 mesozoic or tertiary age. In the middle or central portions 

 of the chain there are a few outliers of secondary formation, 

 but with these exceptions there is an immense blank between 

 the epoch of the carboniferous and geologically recent times. 



All these features of the great Cordillera are found in the 

 mountain system of Tasmania. There is the granite axis, 

 then the metamorphic rocks, the Silurian strata, the 

 Devonian, the carboniferous, and probably the Hawkesbury 

 sandstones. After these and amidst them we have an 

 immense development of intrusive greenstones. Then 

 follows a vast blank, until the tertiary basaltic rocks and 

 alluvial drifts are reached. In the whole island there is not 

 the slightest trace of any marine mesozoic rock. On the 

 extreme north side there is a small patch of miocene tertiary, 

 and no doubt there are other such fragments underlying the 

 basaltic rocks on the low lands of the north coast. Such 

 deposits form no exception to its general resemblance to the 

 great Australian Cordillera. On the low-lying flats of those 

 mountains similar miocene or later formations occur, at least 

 on the side opposite to those of Tasmania. 



Thus we have in Australia and Tasmania a mountain 

 system composed of the same elements, apparently upheaved 

 under the same conditions, probably belonging to the same 

 epoch, and subject to the same changes afterwards. The 

 differences between the two systems are that the development 

 of greenstones is much more extensive in Tasmania than in 

 any equal area in Australia; and the disturbance and 

 dislocations of all the strata have been more violent and 

 numerous. Thus it is that no single formation can he 

 followed for any great distance in Tasmania. It is broken 

 up and faulted and overlaid by the intrusive rock. This 

 has a most important economic bearing on the mineral 

 productions of the rocks. Coal of fine quality and in thick 

 seams is of frequent occurrence in the carboniferous rocks, 

 but mining has not been very successful hitherto, partly 

 because of the continued dislocations or faulting of the 

 seams. It would appear as if the disturbances which during 

 a long course of ages uplifted the Cordillera, had its period 

 of greatest activity in the southern extremity, which is now 

 represented by the Tasmania mountain system. Before 

 dealing with these various formations separately, it will be 

 necessary to say something about the general direction of 

 the mountain ranges of the island. 



