1847.] JUKES ON AUSTRALIA. 245 



2. On the south-eastern portion of Tasmania. 



The two principal rock-masses of the south-eastern portion of Tas- 

 mania are a very massive rudely columnar greenstone, and the sand- 

 stone of the palseozoic formation. The igneous rocks vary from a 

 crystalline dark greenstone, through fine-grained basalts, to a coarse 

 cellular trap or scoriaceous lava-like pumice. The sandstones contain 

 interstratified beds of clay, shale and loose sand, as also of limestone 

 and coal. 



From the want of a good physical map on a sufficiently large scale, 

 and of time for a detailed examination of the country, I am unable to 

 draw any section of any portion of Tasmania, or even to give an accu- 

 rate and positive description of the order of superposition of the stra- 

 tified rocks, or of their relations with the igneous rocks. 



The interior of the country is rugged and broken, with many 

 ranges of hills running in various directions, and the coast-line is in- 

 dented by a multitude of bays, harbours and channels penetrating 

 into the land with much irregularity. To the difficulty thus arising 

 from the external features of the country, is added that resulting 

 from great complexity in its internal structure. The sedimentary and 

 the igneous rocks are so interlaced and entangled one with the other, and 

 their apparent relations at the surface so different in different localities, 

 that nothing but a careful and minute survey, laid down on maps of 

 a large scale, will ever be able thoroughly to elucidate them. 



A. The Valley of the Derwent River. 



Along the S.W. side of the valley of the Derwent runs a bold 

 range of flat-topped hills, of which one of the principal promontories 

 is Mount Wellington, rising immediately behind Hobarton to a height 

 of 4200 feet above the sea. The upper portion of this range is com- 

 posed of massive greenstone, often forming rude columns of great 

 size, frequently as much as ten feet in diameter. The lower slope of 

 this range, and much of the country forming the opposite side of the 

 valley, is composed of the palaeozoic rocks. These lie generally in a 

 nearly horizontal position, and I believe abut horizontally against 

 the greenstones ; but as I never found a clear section near the junction 

 of the two, I cannot positively say that they do not pass imder them, 

 — that the greenstones of the hill-tops are not a thick capping resting 

 on the palaeozoic formation. In ascending Mount Wellington from 

 Hobarton we first pass over a great thickness of white and yellow 

 sandstones nearly horizontal ; above these are shales and thin beds of 

 limestone, hkewise horizontal ; over which again other sandstones are 

 found. These rocks occur to a height of 2500 feet above the sea, 

 and apparently form a solid mass of that thickness at least. Above 

 this point greenstone alone is to be seen, forming a mass 1 700 feet thick 

 at least. Its total thickness depends of course on the undecided ques- 

 tion, of whether it be a capping to the palaeozoic rocks, or what I 

 believe is much more probable, a solid mass with the sedimentary beds 

 resting against its sides. 



Both the sandstones and limestones are quarried at several points. 



