NOTES ON THE MOUNT LYELL DISTRICT, 



TASMANIA. 



By Frederick Danvers Power, F.G-.S. 



(Corresponding Member Royal Society of Tasmania.) 



On taking a casual glance at the geologically coloured map 

 of Tasmania we are struck with its similarity in appearance to 

 some huge concretion, for we see a nucleus of greenstone, 

 which is surrounded more or less by a ring of the upper coal 

 measures, and these again by rocks from other epochs. 



If instead of the geological map we take a topographical 

 one we will observe the same onion -like structure. In the 

 centre we find the Lake Plateau country, from which the 

 river systems of Tasmania radiate. Encircling this are 

 various ranges of mountains, and finally we have the sea 

 coast, which has practically the same contour as the kernel, 

 making due allowance for irregularities, which would be 

 exaggerated by enlargements. Looking at the island as a 

 whole, it is heart-shaped, and somewhat similar in outline to 

 the continents, inasmuch as it is widest at the northern and 

 narrowest at its southern end, its length being north and 

 south. The geological and topographical features coinciding 

 so closely, we are naturally led to the conclusion that they 

 must in some way or other be intimately related. If we can 

 further connect our ore deposits with the physical develop- 

 ments of the country we may gain something by our studies 

 with which the strictest utilitarian cannot find fault. 



Orography. 



Mr. R. M. Johnston supposes that many of the Tasmanian 

 mountains are due to the shrinkage of the earth's crust ; but 

 it has long since been proved that the elevations of our 

 mountains are far in excess of that required by the cooling 

 of the world, and although some slight puckering of the 

 surface may be due to this cause, still I believe it will be 

 generally conceded that other agencies are also at work, and 

 that the presence of the ocean is the greatest of these. 



We almost invariably find that the highest mountain 

 ranges have been developed more or less parallel to the past 

 or present sea coasts that are washed by the largest bodies of 

 water. Thus in South America we find the Andes on the 

 west higher than the mountains of the east coast ; also that 

 the western shores of America are washed by the Pacific 

 Ocean, which is greater in area and depth than the Atlantic, 

 which is on the eastern coast. Coming nearer home for an 

 example, we find the highest Australian mountains on the 



