of the Island of Tasmania. 157 



formed in some places by carboniferous and in others older 

 paleozoic rocks. It did not come from one outlet ; in fact, 

 dykes are as commonly distributed as the stone, but the 

 dykes do not always correspond with the mountains. We 

 must, therefore, imagine that the high-peaked summits 

 crowned with this igneous rock mark former points of ejec- 

 tion. They may in some cases, but in the majority these 

 mountains are the jagged, uneven portions of a surface which 

 has been broken by upheaval, volcanic outbursts, earth- 

 quakes, and dislocations of various kinds, then cut and 

 scarred by the denudation of wind and rain and sea and 

 flood. The evidence of all this is found in the strata below. 

 They are faulted and wedged out by dykes and intrusive 

 masses of rock in many localities ; but there are others 

 where, though the greenstones are in very thick masses 

 above, the strata underneath are very little disturbed. On 

 the extreme west coast, for instance, near Macquarie Har- 

 bour, greenstone occurs only rarely, and then it is at great 

 elevations and in the form of capping to the underlying 

 stratified deposits. According to Mr. Chas. Gould, it has 

 the appearance of outliers from the great mass of trappean 

 rocks upon the east; for the regularity and undisturbed 

 condition of the stratified formations below preclude the idea 

 of its having been ejected through. It seems rather to have 

 flowed across from east to west. Boulders of greenstone 

 occur occasionally of great size and in considerable quantities 

 at distances remote from where it exists in situ. The 

 junction of the greenstone and underlying rocks is at various 

 elevations, and this is not due to any upheaval, but to the 

 irregularly eroded surface upon which it was deposited. It 

 has been suggested that some of the lakes of the interior 

 have been formerly craters, and Lake St. Clair, with a depth 

 of nearly 600 feet, has been especially cited. What lends a 

 colour to this supposition is that it is surrounded by moun- 

 tains of greenstone. But, according to Mr. Gould, sandstone 

 crops out from below the greenstone of Mount Olympus, 

 and these sandstones are nearly horizontal, and there are no 

 scoriae, ashes, or other deposits around the lake.* The 

 more solid portions of ash deposits are often converted 

 into greenstone, and the lighter portions may have easily 



* There is, however, one large deep lake- crater in South Australia named 

 Mount Gambier. The ashes lie there upon perfectly horizontal limestones, 

 which are full of tertiary fossils. 



